Condensed Matter doi: 10.3390/condmat11020021

Authors: Chenxu Jiang Sitong Li Junyu Chen Haoqi Liu Chenyang Jia Changlin Yang Juan Zhang Jiahao Huang Xu Xiao Wenke Xie

Terahertz (THz) metamaterial biosensors have emerged as a powerful platform for label-free, non-ionizing biodetection, yet their clinical translation is severely hindered by limited sensitivity, poor anti-interference capability, and a fragmented research chain that rarely extends beyond simulation. Two-dimensional transition metal carbides/nitrides (MXenes) offer a transformative alternative to conventional gold-based metamaterials, providing metal-like high conductivity, abundant surface functional groups for specific biomolecular capture, excellent biocompatibility, and mechanical flexibility. This review systematically examines the recent progress of MXene-based THz metamaterial biosensors, covering structural design strategies, material synergistic system, machine learning-assisted optimization, and performance evaluation metrics. While most studies remain in the simulation stage, a landmark in vivo validation by Yang et al. achieved real-time thrombus monitoring with 94.7% sensitivity and 92.3% specificity, bridging the gap between simulation and clinical application. We identified key bottlenecks hindering clinical translation and propose future directions toward clinically adaptive, full-chain development. This review provides a roadmap for transitioning MXene-based THz biosensors from laboratory simulation to practical point-of-care diagnostics.

Condensed Matter doi: 10.3390/condmat11020020

Authors: Bin Li

High-temperature superconductivity in strongly correlated materials is often accompanied by pseudogap behavior, strange-metal transport, strong phase fluctuations, and reduced superfluid stiffness, particularly in quasi-two-dimensional systems. These features suggest that pairing alone may not determine the onset of global superconductivity. We develop a coordination-based framework in which superconductivity is promoted by the collective organization of internal electronic degrees of freedom coupled to a carrier phase. A minimal lattice model is introduced, combining a U(1) phase sector, an internal coordination field, and an inter-sector coupling. A Landau analysis shows that internal coordination enhances the effective phase stiffness and can destabilize the incoherent state once the coordination amplitude becomes sufficiently large. Monte Carlo simulations of the model confirm that increasing coordination strength enhances phase stiffness and shifts the onset of global coherence to higher temperature. The framework provides a possible organizing interpretation of the separation between pseudogap onset and superconducting coherence, as well as the sensitivity of layered superconductors to reduced dimensionality, competing orders, and vortex-core structure. It is not intended to replace BCS theory, but to extend phase-stiffness-based descriptions to regimes where pairing, local coordination, and global phase coherence are distinct.

Condensed Matter doi: 10.3390/condmat11020019

Authors: Abigail Lee Jürgen Haase

The electronic properties of high-temperature superconducting cuprates are encoded in NMR data. Without microscopic theory, reliable NMR phenomenologies are in demand. Here we make use of the extensive literature data to develop a different understanding of the cuprates from the shifts of the CuO2 plane. The Cu shift analysis is based only on the symmetry of the two Cu hyperfine couplings, without assumptions about their size. We use an anisotropic Aα and isotropic B, as from atomic Cu orbitals, and find two spin components (A- and B-spins) that explain all the shift data. The components differ in size and temperature dependence according to simple rules. Upon doping the cuprates, metallic B-spin appears above a pseudogap temperature, which is shared with the A-spin. Further doping decreases the pseudogap temperature and increases the B-spin, but less so the A-spin. The apparent linear rate of increase in the density of states of the B-spin with doping is nearly threefold above x=0.20, where the pseudogap disappears. The pseudogap temperature is a measure of the coupling between A and B, which suppresses the shifts but not nuclear relaxation. Spin-singlet pairing involves A and B according to three simple condensation rates, which will be discussed. The optimal Tc demands a special match between A and B. However, the shifts do not simply predict the highest Tc of all cuprates, in contrast to nuclear relaxation anisotropy and charge sharing between planar Cu and O. Relations to other probes are discussed.

Condensed Matter doi: 10.3390/condmat11020018

Authors: Yong Sun Shigeru Kanemitsu

Negative capacitance (NC) has been reported across a wide range of physical systems, yet its interpretation has remained fragmented due to the lack of a unified conceptual framework. Existing explanations—spanning ferroelectric free-energy curvature, tunneling transport, plasmonic resonances, and electronic compressibility—have often been treated as unrelated or even contradictory. This review resolves these inconsistencies by showing that all manifestations of NC arise from non-synchronization between external excitation and internal response. We classify NC into three fundamental categories: temporal mismatch, originating from delays or inertia in charge or polarization dynamics; spatial mismatch, caused by nonuniform field or mode distributions; and quantitative mismatch, resulting from intrinsic parameter reversal such as negative curvature or negative compressibility. Despite their diverse physical origins, these mechanisms share the same mathematical signature (Ceff=∂Q/∂V<0). Organizing NC within this unified framework clarifies long-standing ambiguities, connects previously isolated research fields, and establishes a systematic foundation for engineering NC in electronic, photonic, and quantum devices. The framework further highlights tunnel-current-induced NC as a representative single-particle mechanism within the temporal mismatch category, expanding the scope of NC beyond ferroelectricity and collective modes. Overall, this work positions NC not as a singular anomaly but as a universal response class emerging from the interplay between excitation and internal dynamics.

Condensed Matter doi: 10.3390/condmat11020017

Authors: Xingyu Ma Minghuan Zeng Huaiming Guo Shiping Feng

The transport experiments reveal that the low-temperature resistivity in the normal state of cuprate superconductors is quadratic in temperature (T-quadratic) in the underdoped pseudogap phase, while it is linear in temperature (T-linear) in the overdoped strange-metal phase; however, the full understanding of these different behaviors is still a challenging issue. Here starting from the microscopic electronic structure of cuprate superconductors, the low-temperature resistivity in the normal state is investigated from the underdoped pseudogap phase to the overdoped strange-metal phase. It is shown that the mechanism requires both the impurity scattering and the umklapp scattering: the impurity scattering is needed to restrict the modification of the distribution function to at and around the antinodal region, while the impurity-scattering assisted umklapp scattering from a spin excitation is at the heart of the behavior in the low-temperature resistivity, where the doping dependence of the temperature scale exists, and presents a similar behavior of the antinodal spin pseudogap crossover temperature. In the low-temperature region above the temperature scale in the overdoped strange-metal phase, the resistivity is T-linear; however, in the low-temperature region below the temperature scale in the underdoped pseudogap phase, the opening of the spin pseudogap lowers the spin excitation density of states at and around the antinodal region, which reduces the strength of the electron umklapp scattering from a spin excitation associated with the antinode, and thus leads to a T-quadratic behavior of the resistivity.

Condensed Matter doi: 10.3390/condmat11020016

Authors: Paulo J. F. Cavalcanti Jérôme Cayssol Alexander I. Buzdin

We suggest Josephson interferometry as a quantitative probe of spin–orbit-driven phenomena in superconducting heterostructures. Two distinct mechanisms are analyzed: (i) intrinsic helical superconductivity, producing asymmetric Fraunhofer patterns with lobe deformations and field-reversal asymmetry, and (ii) emergent interfacial magnetism in ferromagnet–superconductor hybrids, where Rashba spin–orbit coupling generates spontaneous fields that rigidly shift the interference fringes. The predicted signatures—flux-shifted interference minima, anisotropic critical current suppression, and angle-dependent pattern distortions—provide direct experimental access to finite-momentum pairing and interface-localized fields via standard Josephson current measurements.

Condensed Matter doi: 10.3390/condmat11020015

Authors: Serguei Brazovskii Natasha Kirova

Six decades ago, the scientist from Stanford University, W.P. Little, announced a crusade to search for superconductivity, assumed to be heat-resistant in organic materials. Although such an ambitious goal was never realized in practice, this proposal gave rise to the entire ecosystem of studies on “synthetic metals,” creating a diverse community of material, experimental, and theoretical activities in low-dimensional electronic systems. We shall briefly review some key steps in this history, examine its main branches, and recall the consequences that remain on the agenda today. Particularly, we shall focus on a phenomenon of electronic ferroelectricity, whose roots can be found in the suggestion of a would-be superconducting polymer.

Condensed Matter doi: 10.3390/condmat11020014

Authors: Krastyo Buchkov Peter Rafailov Nikolay Minev Vladimira Videva Ivalina Avramova Velichka Strijkova Todor Lukanov Dimitre Dimitrov Vera Marinova

The present study focuses on liquid-precursor-mediated chemical vapor deposition (under ambient pressure and moderate temperature range) of WSe2 on sapphire using ammonium meta-tungstate and sodium cholate. The investigation provides additional results and information for the WSe2 cluster formations on sapphire as an extension of our previous study, especially based on structural, chemical and morphological characterization of the observed largest and predominant polygonal WSe2 domains whose lateral size can reach several hundreds of micrometers. In addition, highly symmetrical shapes were also observed. The Raman spectroscopy and atomic force microscopy identified the formation of both mono- and multilayered WSe2. Moreover, the Raman spectrum analysis shows a complex peak structure with unusual splitting effects in the second-order modes marking strong activity of excitonic-resonance processes.

Condensed Matter doi: 10.3390/condmat11020013

Authors: Lady Johana Endo Aguilar Indry Milena Saavedra Gaona Carlos Arturo Parra Vargas Jahaziel Amaya Jaime Ernesto Vargas Daniel Llamosa Pérez

This study investigates magnetic harvesting of Chlorella vulgaris cultivated under saline and wastewater conditions using Fe3O4 and polyethylene-glycol-coated Fe3O4 (Fe3O4@PEG) nanoparticles synthesized by ultrasound-assisted coprecipitation. TEM showed agglomerated, quasi-spherical particles with mean diameters of 13 ± 1 nm (Fe3O4) and 15 ± 1 nm (Fe3O4@PEG). FTIR confirmed the Fe–O vibrational bands of magnetite and the characteristic PEG vibrations in the coated sample. VSM measurements indicated superparamagnetic behavior, with saturation magnetizations of 72.74 emu/g for Fe3O4 and 32.25 emu/g for Fe3O4@PEG. SEM–EDX of native and functionalized cells verified nanoparticle attachment on the algal surface. Magnetic separation experiments (OD684) showed a decrease in supernatant absorbance with increasing nanoparticle dose, consistent with biomass removal; the PEG-coated system showed a lower apparent biomass concentration after functionalization.

Condensed Matter doi: 10.3390/condmat11020012

Authors: Marco A. Camacho-Peralta Israel Betancourt Jose T. Elizalde-Galindo

Mn54Al46 alloys with τ-phase as their main component were successfully obtained in a reproducible processing window combining melt-spinning, annealing at intermediate temperatures (450 °C) and low-energy milling. The complete ε → τ phase transformation was driven by thermal decomposition of ε-phase and favored by high grain boundary density inherent to the melt-spun microstructure. An improved magnetic response of the melt-spun Mn54Al46 alloys was observed, as they exhibited saturation magnetization values between 80 and 90 emu/g, together with intrinsic coercivities around 2000 Oe and Curie temperatures between 640 and 648 K. Significant coercivity enhancement over 6000 Oe was predicted, by means of micromagnetic calculations, for alloys with grain size refinement below 100 nm. The efficient, single-step experimental phase transformation with no additional stabilizers for the τ-phase was explained in terms of microstructural features, whereas magnetic enhancement was attributed to lattice distortions promoted by the milling process. This integrated approach introduces a pathway to achieve τ-phase Mn-Al with tunable magnetic performance useful for applications.

Condensed Matter doi: 10.3390/condmat11020011

Authors: Sakshi Khandal Preksha Gagneja Manas Nasit Sameer Saharan Sarita Khaturia Pratibha Sharma Sujata Kumari P. A. Alvi Naveen Yadav Bon-Heun Koo Shalendra Kumar Kavita Kumari

The multifunctional attributes of SmFeO3 make it a promising candidate for the current diverse technological applications. Therefore, in this work, we investigated the effect of synthesis temperature on the magnetic, optical and electrochemical properties of SmFeO3 nanoparticles at room temperature (SFO-RT) and 50 °C (SFO-50) when prepared through the co-precipitation method. The XRD analysis revealed two distinct phases: SmFeO3 and Sm2O3 as secondary with SmFeO3 emerging as the primary phase (88–93%). The FESEM images showed the amalgamated morphology of the nanoparticles indicating the enhanced thermal kinetics of the solution which not only limited the particle growth but also facilitated their coalition. The band gap energy was found to be 2.2 and 2.3 eV for SFO-RT and SFO-50, respectively, while the values of saturation magnetization noted were 2.14 and 1.53 emu/g for SFO-RT and SFO-50, respectively. The XPS analysis revealed Sm to be in a +3 oxidation state, while Fe was in a mixed (+3/+2) oxidation state showing an increase in the ionic concentration in SFO-50. From the electrochemical measurements, the highest specific capacitance was observed for SFO-50 (65.8 F/g) as compared to SFO-RT (49.3 F/g). The results indicate a clear effect of synthesis temperature on the properties of SmFeO3. Here, two factors played a prominent role: one was the morphology, shaped through the particle growth, and the other was the secondary phase. The decrease in the size of the agglomerated particles and phase fraction of the secondary phase brought about necessary changes in the structural attributes to reduce the saturation magnetization and enhance the specific capacitance of SFO-50. Overall, this study shows that the synthesis temperature affects the crystalline structure and phase fractions leading to the modulation of electronic structure, band gap, magnetic interactions and specific capacitance.

Condensed Matter doi: 10.3390/condmat11010010

Authors: Maria C. Barrero-Moreno Abraham Méndez-Reséndiz Juan C. Carrillo-Rodriguez Andrés M. Garay-Tapia

Two-dimensional (2D) materials, particularly MXenes and transition metal dichalcogenides (TMDs), have attracted intense interest as supercapacitor electrodes due to their high surface area and tunable electronic structure. However, large discrepancies persist between the quantum capacitance values predicted by density functional theory (DFT) calculations and experimentally measured gravimetric capacitances. In this review, we critically analyze DFT methodologies, surface models, normalization strategies, and electrochemical characterization protocols, and compile an extensive dataset of reported MXene and TMD systems to quantify the degree of experimental–theoretical agreement. We show that MXenes typically achieve less than 20% of their predicted capacitance because of restacking, surface terminations, and limited ion accessibility, whereas TMDs exhibit substantially better correspondence, often approaching or exceeding 70% of theoretical values. These results indicate that the theoretical capacitance predicted by DFT is primarily determined by the electronic structure of the material, which defines the upper limit of charge storage, whereas the experimentally achieved capacitance is largely controlled by morphological factors, surface chemistry, and electrode architecture that limit ion accessibility.

Condensed Matter doi: 10.3390/condmat11010009

Authors: Yong Sun Shigeru Kanemitsu

A capacitor modeled as a parallel combination of a resistance (R) and a capacitance (C) exhibits three distinct operating regimes when both parameters depend on the applied voltage (V): a positive-capacitance regime (dR/R>dV/V), an Ohmic regime (dR/R=dV/V), and a negative-capacitance regime (dR/R<dV/V). In the limit (R→∞), the device behaves as a conventional permittivity-based capacitor, whereas in the limit (R→0), negative capacitance emerges due to nonlinear current–voltage characteristics. To verify this mechanism, we fabricated nanometer-spaced two-electrode structures using multi-walled carbon nanotubes (MWCNTs) and Si crystals. The measurements confirmed negative capacitance consistent with theoretical predictions. Unlike ferroelectric negative capacitance, the effect demonstrated here arises solely from the nonlinear I–V characteristics at the electrode interfaces, without involving any ferroelectric polarization dynamics. This negative capacitance can be interpreted as an equivalent inductance, enabling a two-dimensional tunable reactance element (TDTRE) that operates without electromagnetic coupling and is compatible with conventional IC technologies.

Condensed Matter doi: 10.3390/condmat11010008

Authors: Robert Prater Mingkun Chen Matthew Staab Sudheer Sreedhar Journey Byland Zihao Shen Sergey Y. Savrasov Valentin Taufour Vsevolod Ivanov Inna Vishik

In this paper, we present a comprehensive study of the electronic structure of CeCoGe3 throughout the entire Brillouin zone in the non-magnetic regime using angle-resolved photoemission spectroscopy (ARPES). The electronic structure agrees in large part with first principles calculations, including predicted topological nodal lines. Two new features in the band structure are also observed, namely a surface state and folded bands, the latter of which is argued to originate from a unit cell reconstruction.

Condensed Matter doi: 10.3390/condmat11010007

Authors: Ginevra Lalle Alessandro Maurizi Anna Giusti Grigore Leahu Gianmario Cesarini Emilija Petronijevic Alesandro Belardini Roberto Li Voti

In this work, thermal imaging is employed to study the opto-thermal response of apples (Malus domestica Borkh.), assessing their post-harvest evolution through the estimation of thermal diffusivity. A non-destructive experimental procedure based on mid-wave infrared (MWIR) thermal camera (3–5 µm) and localized heating with a visible laser is developed, enabling spatially and temporally resolved surface temperature measurements. Temperature fields are recorded at different time points and radial distances from the heated spot. A theoretical model based on Fourier thermal diffusion equation is formulated to describe the spatio-temporal evolution of surface temperature. After validation on a reference sample, the method is applied to Golden and Red Delicious apples over a 28-day storage period at room temperature. Red Delicious apple exhibits higher mean diffusivity values without significant temporal changes, whereas a progressive increase in diffusivity is observed for Golden Delicious apples. These results show that thermal diffusivity is sensitive to post-harvest physiological changes in apple tissue and may be associated with intrinsic properties such as tissue density and water content. By relating laser-induced temperature fields to the estimation of thermal diffusivity, this approach enables the non-destructive, quantitative assessment of thermal diffusivity, showing potential for fruit maturity and quality assessment, which are of high importance in agri-food monitoring applications.

Condensed Matter doi: 10.3390/condmat11010006

Authors: Jeton Halili Kledi Xhaxhiu Nensi Isak Makfire Sadiku Arianit Reka Muhamed Farruku Avni Berisha

Water pollution from phenols remains a critical concern due to their persistence, toxicity, and industrial prevalence. Graphene oxide (GOx), with its functional groups and large surface area, offers strong adsorption potential. Using density functional theory (DFT), reduced density gradient (RDG), and quantitative structure–activity relationship (QSAR), we examined how protonation and substituents influence phenol adsorption. Deprotonated phenolates bind more strongly to GO than neutral species via electrostatics and H-bonding. Substituents alter affinity: halogens enhance it, bulky alkyls hinder it, and nitro groups show electron-withdrawing effects. Bisphenolate A displayed multidentate binding. QSAR models reproduced DFT energies with R2 > 0.99, enabling fast prediction. These results highlight how pH speciation and substituents govern adsorption on GO, guiding the design of efficient water treatment materials.

Condensed Matter doi: 10.3390/condmat11010005

Authors: Daniel Bandur Abigail Lee Jakob Nachtigal Stefan Tsankov Jürgen Haase

Cuprates currently hold the record for the highest temperature superconductivity at ambient pressure, but the microscopic understanding of these materials remains elusive. Here, we utilize nuclear magnetic resonance (NMR) data of planar oxygen and copper from essentially all hole-doped cuprates to provide a universal phenomenology relating the NMR spin shifts, which measure the electronic spin polarization at a given nucleus, with the superconducting dome and maximum critical temperature. There appear to be two separate contributions to the spin shift in planar copper, only one of which is seen at the oxygen site, and we associate them with two different types of carriers. Upon disentangling these two components, their relative size is shown to correlate not only with the doping dependence of the superconducting dome but also with the variation in maximum superconducting critical temperature, Tc,max, between different families. One of these components is independent of family and resides in the hybridized planar orbitals of Cu and O. The second component, in contrast, is predominately isotropic and encodes the differences between the families. It is thus related to the charge transfer gap and planar hole sharing. Our findings offer universal insight which should prove useful in the continuing development of a comprehensive theory of the cuprates, as well as an indication of how it may be possible to engineer materials with higher critical temperatures.

Condensed Matter doi: 10.3390/condmat11010004

Authors: Takeshi Egami

Strong electron correlation plays a central role in the high-temperature superconductivity (HTSC) of cuprates. However, to date, research has focused only on its role in spin dynamics and related effects, even though it is becoming increasingly clear that spin alone may not be sufficient to create HTSC. Here, we discuss a possible role of electron correlation in the Bose–Einstein condensation (BEC) of Cooper pairs. Recently, we succeeded in observing dynamic electron correlation via inelastic X-ray scattering through results presented in real space. We discovered that electron correlations are strongly modified in the plasmon, proving that electron dynamics significantly affect electron correlation. Earlier, we found that in 4He, the atom–atom distance in the BE condensate is 10% longer than that in the non-condensate. These results suggest the possibility that the reduction in electron-repulsion energy upon BEC is driving Tc to high values. Thus, electron correlation itself could be the origin of the HTSC phenomenon.

Condensed Matter doi: 10.3390/condmat11010003

Authors: Pablo P. Yepes

The implementation of FLASH Radiotherapy (FLASH-RT), characterized by ultra-high dose rates (UHDRs) frequently exceeding 106 Gy/s in microsecond pulses, imposes stringent requirements on real-time dosimetry. Conventional ionization chambers suffer severe ion recombination and space-charge limitations under these conditions. This review summarizes the state of SSD technologies—including conventional standard silicon diodes, advanced SiC diodes, Low-Gain Avalanche Detectors (LGADs), and pixel detectors—and compares their performance, linearity, and dynamic range in UHDR environments. Particular attention is devoted to operational modes (integrating vs. counting), saturation mechanisms, and readout electronics, which frequently dominate detector behavior at FLASH conditions. We discuss the experimental results from recent UHDR beamlines and highlight emerging concepts that will shape future clinical translation.

Condensed Matter doi: 10.3390/condmat11010002

Authors: A. G. Marinopoulos

Hydrogen is frequently incorporated in alkaline-earth oxides during crystal growth or post-deposition annealing. For MgO, several studies in the past showed that interstitial monatomic hydrogen can also favourably bind with oxygen vacancies to form stable substitutional defect complexes (substitutional hydrogen or U-defect centers). The present study reports first-principles density-functional calculations of the formation energies of both interstitial and substitutional forms of the hydrogen impurity in MgO. Determination of the site-resolved densities of electronic states allowed for a detailed identification of the nature of the impurity-induced levels, both in the valence-energy region and inside the band gap of the host. The stability and diffusion mechanisms of both hydrogen defects was also studied with the aid of nudged elastic-band (NEB) calculations. Interstitial hydrogen was found to be an amphoteric defect with the lower formation energy for any realistic environment conditions (temperature and oxygen partial pressure). The NEB calculations showed that it is a fast-diffusing species when it is thermodynamically stable as a positively-charged state (bare proton). In contrast, the hydrogen-vacancy complex is a shallow donor, extremely stable against dissociation and virtually immobile as an isolated defect. Its formation is found to be favoured for a range of mid-gap Fermi-level positions where positively-charged interstitial hydrogen and neutral oxygen vacancies (F centers) are both thermodynamically stable low-energy defects. The present findings are consistent with the established consensus on the electrical activity of hydrogen in MgO as well as with experimental observations reporting the remarkable thermal stability of substitutional hydrogen defects and their ability to act as electron traps.

Condensed Matter doi: 10.3390/condmat11010001

Authors: Melissa L. Casais-Molina César A. Cab Rubén A. Medina-Esquivel Jorge A. Tapia

The mechanical properties of cubic (c-BN) and wurtzite (w-BN) boron nitride structures were investigated and compared using density functional theory (DFT) with several exchange–correlation functionals. This research focuses on determining the bulk modulus (B) and, for the first time, the stretching bond force constants (kr), two fundamental parameters that describe the intrinsic stiffness and elastic resistance of these BN structures. Despite their structural similarity with the same tetrahedral coordination between atoms, c-BN and w-BN exhibit subtle differences in bond strength and compressibility that have not been fully clarified at the atomistic level. By systematically analyzing the influence of hybrid and semi-local functionals, consistent relationship between structural configuration and the predicted B and kr values of both c-BN and w-BN structures were established and compared. These findings not only validate DFT as a reliable approach for assessing the mechanical properties of BN polymorphs, but also offer key parameters for machine learning and advanced multiscale modeling. Therefore, this theoretical study contributes to understanding the origin of mechanical properties in BN structures and supports their design in applications where a particular hardness and stability are required.

Condensed Matter doi: 10.3390/condmat10040064

Authors: Izumi Hase

Flat electronic bands, characterized by a nearly dispersionless energy spectrum, have emerged as fertile ground for exploring strong correlation effects, unconventional magnetism, and topological phases. This review paper provides an overview of the theoretical basis, material realization, and emergent phenomena associated with flat bands. We begin by discussing the geometric and topological origins of flat bands in lattice systems, emphasizing mechanisms such as destructive interference and compact localized states. We will also explain the relationship between quantum metrics and flat bands, which are recent theoretical findings. We then survey various classes of materials—ranging from engineered lattices and Moiré structures to transition metal compounds—where flat bands have been theoretically predicted or experimentally observed. The interplay between flat-band physics and strong correlations is explored through recent developments in ferromagnetism, superconductivity, and various Hall effects. Finally, we outline open questions and potential directions for future research, including the quest for ideal flat-band systems, the role of spin–orbit coupling, and the impact of disorder. This review aims to bridge fundamental concepts with cutting-edge advances, highlighting the rich physics and material prospects of flat bands.

Condensed Matter doi: 10.3390/condmat10040063

Authors: Bingqian Zhang Junhao Zhu Zhihua Yuan Peide Han

Graphene holds significant promise as an ideal reinforcing phase. However, its tendency to irreversibly aggregate and its unclear impact on electrodeposition mechanisms have hindered the full exploitation of its advantages for enhancing material mechanical properties. In this study, we produced a graphene/Ni composite reinforced with reduced graphene oxide (rGO) via a simple, scalable, and cost-effective electrodeposition approach. The incorporation of graphene not only raised the cathodic polarization potential but also enhanced the transport of ions. As a result, the presence of rGO significantly influenced the grain size, grain distribution, and the proportion of growth twins-3(111). Compared with Ni, the graphene/Ni composite exhibited improvements of 14.8% in strength and 16.8% in fracture elongation. Additionally, first-principles calculations confirmed that superior electronic conductivity and all elastic moduli along with Poisson’s ratio were found to be higher in the composite. Our findings offer fundamental insights into the role of rGO in governing the structural evolution of graphene/metal composites.

Condensed Matter doi: 10.3390/condmat10040062

Authors: Svetlana Kalinichenko Maksim Pudovkin

The studied Ce0.5Y0.5−XTbXF3 (X = 0, 0.001, 0.002, 0.005, 0.01, and 0.05) nanoparticles were synthesized via the water-based co-precipitation method. All the samples demonstrated diameters in the 17–20 nm range and a hexagonal phase corresponding to the phase of CeF3. Under 266 nm excitation (4f–5d absorption band of Ce3+), the luminescence spectrum shape was notably dependent on temperature. The integrated luminescence intensity ratio (LIR) of Ce3+ and Tb3+ (5D4–7F3) peaks was chosen as a temperature-dependent parameter. It was shown that the LIR functions linearly decay. The rate of decay decreases with the increase in Tb3+ concentration. This was explained by the fact that in the case of low Tb3+ concentrations, the spectral temperature dependence is mostly based on effective thermal quenching of Ce3+ luminescence. At higher Tb3+ concentrations, there is a higher probability of Ce3+ to Tb3+ energy transfer. Here, the efficiency of the temperature dependence of this process is lower, and the rate of LIR decay is lower as well.

Condensed Matter doi: 10.3390/condmat10040061

Authors: Aiying Zhao Richard A. Klemm Qiang Gu

We investigate the influence of Landau Levels (LLs) and Zeeman energy, induced by an applied magnetic field B, on the critical temperature Tc for two-dimensional (2D) ultraclean superconductors using a fully quantum mechanical approach within the Bardeen–Cooper–Schrieffer (BCS) theory. In contrast to standard BCS theory, it allows for Cooper pair formation between electrons with opposite spins and momenta along the B direction, both on the same or on neighboring LLs. Our quantum mechanical treatment of LLs reveals that the critical temperature Tc for electrons paired on the same LL exhibits oscillations around the BCS critical temperature at low magnetic fields. The Zeeman energy leads to a decrease in Tc(B) with increasing B for electrons paired both on the same and on neighboring LLs. Notably, as the g-factor increases, Tc(B) decreases faster as the magnetic field increases for a larger g-factor than for a smaller one.

Condensed Matter doi: 10.3390/condmat10040060

Authors: Satoru Hayami

We theoretically investigate topological transitions between coplanar and noncoplanar magnetic states in centrosymmetric itinerant magnets on a square lattice. A canonical effective spin model incorporating bilinear and biquadratic exchange interactions at finite wave vectors is analyzed to elucidate the emergence of multiple-Q magnetic orders. By taking into account high-harmonic wave-vector interactions, we demonstrate that a coplanar double-Q spin texture continuously evolves into a noncoplanar triple-Q state carrying a finite scalar spin chirality. The stability of these multiple-Q states is examined using simulated annealing as a function of the relative strengths of the high-harmonic coupling, the biquadratic interaction, and the external magnetic field. The resulting phase diagrams reveal a competition between double-Q and triple-Q states, where the noncoplanar triple-Q phase is stabilized through the cooperative effect of the high-harmonic and biquadratic interactions. Real-space spin textures, spin structure factors, and scalar spin chirality distributions are analyzed to characterize the distinct magnetic phases and the topological transitions connecting them. These findings provide a microscopic framework for understanding the emergence of noncoplanar magnetic textures driven by the interplay between two- and four-spin interactions in centrosymmetric itinerant magnets.

Condensed Matter doi: 10.3390/condmat10040059

Authors: Mukunda P. Das Frederick Green

This article provides an overview of the role of microscopic conservation in charge transport at small scales and at driving fields beyond the linear-response limit. As a practical example, we recall the measurement and theory of interband coupling effects in a quantum point contact driven far from equilibrium.

Condensed Matter doi: 10.3390/condmat10040058

Authors: Soumyaditya Das Soumyajyoti Biswas Muktish Acharyya Bikas K. Chakrabarti

We briefly review the early development of the mean-field dynamics for cooperatively interacting quantum many-body systems, mapped to pseudo-spin (Ising-like) systems. We start with (Anderson, 1958) pseudo-spin mapping the BCS (1957) Hamiltonian of superconductivity, reducing it to a mean-field Hamiltonian of the XY (or effectively Ising) model in a transverse field. Then, we obtain the mean-field estimate for the equilibrium gap in the ground-state energy at different temperatures (gap disappearing at the transition temperature), which fits Landau’s (1949) phenomenological theory of superfluidity. We then present in detail a general dynamical extension (for non-equilibrium cases) of the mean-field theory of quantum Ising systems (in a transverse field), following de Gennes’ (1963) decomposition of the mean field into the orthogonal classical cooperative (longitudinal) component and the quantum (transverse) component, with each of the component following Suzuki–Kubo (1968) mean-field dynamics. Next, we discuss its applications to quantum hysteresis in Ising magnets (in the presence of an oscillating transverse field), to quantum heat engines (employing the transverse Ising model as a working fluid), and to the quantum annealing of the Sherrington–Kirkpatrick (1975) spin glass by tuning down (to zero) the transverse field, which provides us with a very fast computational algorithm, leading to ground-state energy values converging to the best-known analytic estimate for the model. Finally, we summarize the main results obtained and draw conclusions about the effectiveness of the de Gennes–Suzuki–Kubo mean-field equations for the study of various dynamical aspects of quantum condensed matter systems.

Condensed Matter doi: 10.3390/condmat10040057

Authors: Oleksandr Pastukh

Owing to their dimensions and high aspect ratio, magnetic nanowires possess distinctive physical and chemical properties and are of great importance in building nanoelectronics devices. Nanowires are traditionally produced by electrochemical deposition methods using alumina or polycarbonate membranes, and their parameters (porosity, size, and arrangement of pores) strongly influence the magnetic properties of nanowires. However, very often, the effect that cannot be neglected during synthesis is overdeposition. The influence of overdeposition on the magnetic properties of nanowires is often overlooked, but it can strongly alter the magnetic behavior of the system. In this study, we use micromagnetic simulations to investigate how different levels of overdeposition affect the hysteretic behavior of nanowires and their magnetization switching mechanism. It was shown that the formation of hemispherical caps on the ends of the nanowires may alter the out-of-plane magnetic anisotropy of the nanowires and strongly influence the squareness of the hysteresis loop. The demagnetizing field distribution for nanowires with overdeposition was also investigated, showing a strong influence of its spatial distribution change on the reversal mechanism and interaction between nanowires. The obtained results were compared to existing experimental observations, showing good agreement with the magnetic behavior of the system. Performed research can be of great interest to experimental groups, as it highlights the importance of controlling overdeposition during nanowire synthesis and its potential influence on magnetic performance.

Condensed Matter doi: 10.3390/condmat10040056

Authors: Annette Bussmann-Holder Jürgen Haase Hugo Keller Reinhard K. Kremer Sergei I. Mukhin Alexey P. Menushenkov Andrei Ivanov Alexey Kuznetsov Victor Velasco Steven D. Conradson Gaetano Campi Antonio Bianconi

Low-temperature superconductivity has been known since 1957 to be described by BCS theory for effective single-band metals controlled by the density of states at the Fermi level, very far from band edges, the electron–phonon coupling constant l, and the energy of the boson in the pairing interaction w0, but BCS has failed to predict high-temperature superconductivity in different materials above about 23 K. High-temperature superconductivity above 35 K, since 1986, has been a matter of materials science, where manipulating the lattice complexity of high-temperature superconducting ceramic oxides (HTSCs) has driven materials scientists to grow new HTSC quantum materials up to 138 K in HgBa2Ca2Cu3O8 (Hg1223) at ambient pressure and near room temperature in pressurized hydrides. This perspective covers the major results of materials scientists over the last 39 years in terms of investigating the role of lattice inhomogeneity detected in these new quantum complex materials. We highlight the nanoscale heterogeneity in these complex materials and elucidate their special role played in the physics of HTSCs. Especially, it is highlighted that the geometry of lattice and charge complex heterogeneity at the nanoscale is essential and intrinsic in the mechanism of rising quantum coherence at high temperatures.

Condensed Matter doi: 10.3390/condmat10040055

Authors: Alberto Tufaile Adriana Pedrosa Biscaia Tufaile

This study investigates the dynamic magneto-optical properties of ferrofluid thin films, focusing on how magnetic fields induce light–matter interactions using a device known as Ferrocell. Our findings reveal that incident light interacts with self-assembled, anisotropic nanoparticle structures, transforming the ferrofluid into a highly responsive optical medium. Monochromatic laser experiments confirmed the direct correlation between laser color and diffracted light color offering direct insights into particle orientation and aggregate morphology. We observed significant chromatic shifts, especially in regions under strong perpendicular magnetic fields, which provide compelling evidence of structural colors. This phenomenon stems from wavelength-selective interference and diffraction, reminiscent of photonic crystal behavior, yet characterized by short-range order, classifying the material as a photonic glass.

Condensed Matter doi: 10.3390/condmat10040054

Authors: Antonio Bianconi

The National Laboratories in Frascati (LNF INFN) were conceived and created by a group of collaborators of Enrico Fermi, including Edoardo Amaldi, Gilberto Bernardini, and Enrico Persico, after World War II, with the goal of hosting a 1 GeV electron synchrotron for nuclear physics [...]

Condensed Matter doi: 10.3390/condmat10040053

Authors: Abhisek Bandyopadhyay Dheeraj Kumar Pandey Carlo Meneghini Anna Efimenko Marco Moretti Sala Sugata Ray

We experimentally investigate the structural, magnetic, transport, and electronic properties of two d5 iridate double perovskite materials La2BIrO6 (B = Mg, Zn). Notably, despite similar crystallographic structure, the two compounds show distinctly different magnetic behaviors. The M = Mg compound shows an antiferromagnetic-like linear field-dependent isothermal magnetization below its transition temperature, whereas the M = Zn counterpart displays a clear hysteresis loop followed by a noticeable coercive field, indicative of ferromagnetic components arising from a non-collinear Ir spin arrangement. The local structure studies authenticate perceptible M/Ir antisite disorder in both systems, which complicates the magnetic exchange interaction scenario by introducing Ir-O-Ir superexchange pathways in addition to the nominal Ir-O-B-O-Ir super-superexchange interactions expected for an ideally ordered structure. While spin–orbit coupling (SOC) plays a crucial role in establishing insulating behavior for both these compounds, the rotational and tilting distortions of the IrO6 (and MO6) octahedral units further lift the ideal cubic symmetry. Finally, by measuring the Ir-L3 edge resonant inelastic X-ray scattering (RIXS) spectra for both the compounds, giving evidence of spin–orbit-derived low-energy inter-J-state (intra t2g) transitions (below ~1 eV), the charge transfer (O 2p → Ir 5d), and the crystal field (Ir t2g → eg) excitations, we put forward a qualitative argument for the interplay among effective SOC, non-cubic crystal field, and intersite hopping in these two compounds.

Condensed Matter doi: 10.3390/condmat10040052

Authors: Duvalier Madrid-Úsuga Omar J. Suárez Alfonso Portacio

This study presents a computational investigation into the design of triphenylamine-based donor chromophores incorporating 2-(1,1-dicyanomethylene)rhodanine as the acceptor unit. Three molecular architectures (System-1 to System-3) were developed by introducing distinct thiophene-derived π-bridges to modulate their electronic and optical characteristics for potential application in bulk heterojunction organic solar cells (OSCs). Geometrical optimizations were performed at the B3LYP/6-31+G(d,p) level, while excited-state and absorption properties were evaluated using TD-DFT with the CAM-B3LYP functional. Frontier orbital analysis revealed efficient charge transfer from donor to acceptor moieties, with System-3 showing the narrowest HOMO–LUMO gap (1.96 eV) and the lowest excitation energy (2.968 eV). Charge transport properties, estimated from reorganization energies, indicated that System-2 exhibited the most favorable balance for ambipolar transport, featuring the lowest electron reorganization energy (0.317 eV) and competitive hole mobility. Photovoltaic parameters calculated with PC61BM as acceptor predicted superior Voc, Jsc, and fill factor values for System-2, resulting in the highest theoretical power conversion efficiency (10.95%). These findings suggest that π-bridge engineering in triphenylamine-based systems can significantly enhance optoelectronic performance, offering promising donor materials for next-generation OSC devices.

Condensed Matter doi: 10.3390/condmat10030051

Authors: Fernando Flores Daniel G. Trabada Álvaro Martín-Rodero José Ortega

In order to elucidate the mechanism creating superconductivity in the 2-dimensional layer of a p-doped Sn/Si(111) surface, we have analyzed the many-body effects associated with the electron-phonon (e-ph) coupling and the electron–electron interaction. First, we have calculated the DFT surface band of the system and the coupling associated with the different interactions. In our calculations we find a mean field (DFT) electron bandwidth of 0.54 eV, an attractive coupling Uneg=0.32 eV associated with the e-ph coupling and an effective electron–electron Hubbard repulsion of U=0.83 eV. Then, we analyze the Hubbard Hamiltonian, neglecting in this step the e-ph coupling that is much smaller than the Hubbard coupling, by considering a p-doping in this Hamiltonian of 10%; by means of a Dynamical Mean Field (DMF) approach combined with an interpolative calculation for the self-energy, we deduce the local density of states (DOS) and show that the quasi-particle DOS induced by the doping is not large enough to induce magnetism in the Sn-monolayer. This leads us to analyze the possibility of having superconductivity by considering the attractive interaction induced by the e-ph coupling within an appropriate BCS-Hamiltonian. Our calculations show that the quasiparticle metallic system has a superconductivity critical temperature of ≈7–9 K, in good agreement with experiments.

Condensed Matter doi: 10.3390/condmat10030050

Authors: Nicolás Legnazzi Omar Osenda

The study of new nanoscopic heterostructures composed of different materials follows the idea that the presence of boundary conditions, interfaces and combinations of materials will produce appropriate spectral properties or quantum states, resulting in new devices. Here, we present a detailed study of two kinds of nanowires formed using topological insulators. First, we consider cylindrical nanowires with a cylindrical core of constant radius along the wire, covered by a shell of uniform width. The core and the shell materials are different topological insulators. We thoroughly study the spectra of distinct wires, considering combinations of materials and sizes of the core and shell radii. We also study the expectation values of the spin operators. Then, we consider wires with only a cylindrical shell. For this case, we pay special attention to the limit when the width of the shell is approximately an order of magnitude smaller than the inner and outer radii of the shell. As we use a high-accuracy variational method to obtain the spectra and quantum states, we also study information-like quantities such as the fidelity and quantum entropy of the topological and normal states of the wires.

Condensed Matter doi: 10.3390/condmat10030049

Authors: Shu-Ke Xuan Yuan-Fang Yue Xiao-Ming Li Xun-Wang Yan

Based on first-principles calculations, we systematically investigate the crystal structure, electronic structure, and superconductivity of metallic lead under pressure. The results show that with the increase of pressure, the crystal structure of lead evolves from face-centered cubic (fcc) to hexagonal close-packed (hcp) and then to body-centered cubic (bcc). In different crystal structure phases, the variation laws of electronic structure and superconducting properties with pressure are studied. It is found that the superconducting transition temperature decreases with the increase of pressure in fcc, hcp, and bcc phases. The physical mechanism for this change is explained. The calculation results indicate that elemental metallic lead remains metallic with the increase of pressure, but the electron density of states at the Fermi level decreases, leading to the decrease of the electron-phonon coupling constant (λ) and superconducting transition temperature (Tc) from 7.1 K to 0.04 K. In addition, with the increase of pressure, there is no phenomenon of s electrons transforming into d electrons, which is different from the superconducting behavior of zirconium metal under pressure. These studies explain the superconductivity of elemental metallic lead under high pressure and provide theoretical support for the experiments and applications of lead-based superconductors.

Condensed Matter doi: 10.3390/condmat10030048

Authors: Dimosthenis Stamopoulos

Maxwell’s equations epitomize our knowledge of standard electromagnetic theory in vacuums and matter. Here, we report the clearcut results of an extensive, ongoing investigation aiming to mathematically digest Maxwell’s equations in virtually all problems based on the three standard building units, dielectric and magnetic, found in practice (i.e., spheres, cylinders and plates). Specifically, we address the static/quasi-static case of a linear, homogeneous and isotropic dielectric and magnetic sphere subjected to a DC/low-frequency AC external scalar potential, (vector field, ), of any form, produced by a primary/free source residing outside the sphere. To this end, we introduce an expansion-based mathematical strategy that enables us to obtain immediate access to the response of the dielectric and magnetic sphere, i.e., to the internal scalar potential, (vector field, ), produced by the induced secondary/bound source. Accordingly, the total scalar potential, = + (vector field, = + ), is immediately accessible as well. Our approach provides ready-to-use expressions for and ( and ) in all space, i.e., both inside and outside the dielectric and magnetic sphere, applicable for any form of (). Using these universal expressions, we can obtain and ( and ) in essentially one step, without the need to solve each particular problem of different () every time from scratch. The obtained universal relation between and ( and ) provides a means to tailor the responses of dielectric and magnetic spheres at all instances, thus facilitating applications. Our approach surpasses conventional mathematical procedures that are employed to solve analytically addressable problems of electromagnetism.

Condensed Matter doi: 10.3390/condmat10030047

Authors: Orlando Panella Simone Pacetti Giorgio Immirzi Yogendra Srivastava

After a just tribute to Guido Barbiellini, we show how the notion of a maximum force (Fmax=c4/4G≃3×1043 Newtons) present on the event horizon of a black hole (BH) can be used in conjunction with the Wilson area rule to obtain the surface confinement of the mass of a BH analogous to the surface confinement of quarks. This is then translated into the central result of the paper that PeV scale protons exist on the surface of the Kerr BH residing at our galactic center, a result in complete agreement with the HAWC Collaboration result of a Pevatron at the galactic center. We conjecture that the supermassive BHs present at the center of most galaxies are not born out of a galactic collapse but that they must have been present since the formation of their hosting galaxy.

Condensed Matter doi: 10.3390/condmat10030046

Authors: Er’el Granot

The Landauer-Büttiker formalism provides a fundamental framework for mesoscopic transport, typically expressing conductance in units of the quantum of conductance, e2/h. Here, we present a theoretical study of electron transport in a quasi two-dimensional (2D) quantum wire. This system features a wide transverse confinement and a longitudinal, high-energy, narrow potential barrier. The derivation, performed within the Landauer framework, yields an analytical expression for the total conductance that is explicitly independent of Planck’s constant (h). Instead, the conductance is found to depend solely on the Fermi energy, the electron effective mass, the wire width, and the effective barrier strength. We interpret this as an emergent phenomenon where the explicit signature of the electron’s wave-like nature, commonly manifest through Planck’s constant (h) in the overall scaling of conductance, is effectively absorbed within the energy- and geometry-dependent sum of transmission probabilities. This allows the conductance to be primarily governed by the Fermi energy, representing a ‘state-counting’ quantum parameter rather than more wave-like characteristic.

Condensed Matter doi: 10.3390/condmat10030045

Authors: Ivan Arraut

By using both the weak-value formulation as well as the standard probabilistic approach, we analyze Hardy’s experiment introducing a complex and dimensionless parameter (ϵ), which eliminates the assumption of complete annihilation when both the electron and the positron departing from a common origin cross the intersection point P. We then find that the paradox does not exist for all the possible values taken by the parameter. The apparent paradox only appears when ϵ=1, which is just a singular value. In this paper we demonstrate that this particular value is forbidden inside the scenario proposed by the experiment.

Condensed Matter doi: 10.3390/condmat10030044

Authors: Min Li Haoyan Zheng Xianliang Ke Dawei Zhang Jie Huang

The two-dimensional (2D) Ruddlesden–Popper perovskite exhibits superior chemical stability but suffers from compromised photoelectric properties due to the van der Waals gap. This study presents a novel investigation of surface passivation effects on quasi-2D perovskite X2Csn−1PbnI3n+1 (n = 1–6; X = MA, FA, PEA) using DFT methods, revealing three key advances: First, we demonstrate that organic cation passivation (MA+, FA+, PEA+) enables exceptional stability improvements, with FA-passivated structures showing optimal stability—a crucial finding for materials design. Second, we identify a critical thickness effect (n > 3) where bandgaps converge to <1.6 eV (approaching bulk values) while maintaining strong absorption, establishing the minimum layer requirement for optimal performance. Third, we reveal that effective masses balance and absorption strengthens significantly when n > 3. These fundamental insights provide a transformative strategy to simultaneously enhance both stability and optoelectronic properties in quasi-2D perovskites.

Condensed Matter doi: 10.3390/condmat10030043

Authors: Antoine Suarez

This contribution aims to honour Guido Barbiellini’s profound interest in the interpretation and impact of quantum mechanics by examining the implications of the so-called before–before Experiment on quantum entanglement. This experiment was inspired by talks and discussions with John Bell at CERN. This was during the years when John and Guido co-worked, promoting the mission of the laboratory: “to advance the boundaries of human knowledge”. As the experiment uses measuring devices in motion, it can be considered a complement to entanglement experiments using stationary measuring devices, which have meanwhile been awarded the 2022 Nobel Prize in Physics. The before–before Experiment supports the idea that the quantum realm exists beyond space and time and that the quantum state is a real mental entity concerning choices. As it also leads us to a better understanding of the ‘quantum collapse’ and the measurement process, we pay homage to Guido’s work on detectors, such as his collaborations on the DELPHI experiment at CERN, on cosmic ray detection at the International Space Station, and gamma-ray astrophysics during a large NASA space mission.

Condensed Matter doi: 10.3390/condmat10030042

Authors: Paolo Crivelli Martina Mongillo

This mini-review traces the evolution of axion searches at the CERN Super Proton Synchrotron (SPS), beginning with the early proposal by Guido Barbiellini in 1982 and culminating in the recent advances of the NA62 and NA64 experiments. We discuss the experimental strategies employed in early beam dump searches, the current status of axion and axion-like particle (ALP) searches at the CERN SPS and future directions. This review serves as a tribute to Guido Barbiellini’s scientific legacy and his visionary contributions to this field.

Condensed Matter doi: 10.3390/condmat10030041

Authors: Shafaq Arif Amna Sarwar M. S. Anwar

Cobalt and Nickel (Co, Ni) co-doped magnesium oxide (MgO) nanoparticles (NPs) have been synthesized using the coprecipitation method. The structural, chemical, and optical properties of the as-synthesized NPs are systematically investigated using X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), and UV-visible spectroscopy. It is found that the optical bandgap of co-doped MgO NPs reduces from 2.30 to 1.98 eV (14%) with increasing Ni dopant concentrations up to 7%. The Co0.05Ni0.07Mg0.88O NPs exhibit a high photocatalytic degradation efficiency of 93% for methylene blue dye (MB) under natural sunlight irradiation for 240 min. Our findings indicate that the Co0.05NixMg0.95−xO NPs have strong potential for use as photocatalysts in industrial wastewater treatment.

Condensed Matter doi: 10.3390/condmat10030040

Authors: Ravi Kiran Dimitar Pashov Mark van Schilfgaarde Mikhail I. Katsnelson Arghya Taraphder Swagata Acharya

Hyperbolic plasmons are a highly desired property in optoelectronics and biomolecular sensing. The necessary condition to realize hyperbolic plasmons is a significant anisotropy of the principal components of the dielectric function, such that at a certain frequency range, one component is negative and the other is positive, i.e., one component is metallic, and the other one is dielectric. Here, we study the effect of anisotropy in ReS2, and our theory shows that ReS2 can host hyperbolic plasmons in the ultraviolet frequency range. The operating frequency range of the hyperbolic plasmons can be tuned with the number of ReS2 layers. However, we note that the significantly large imaginary part of the macroscopic dielectric response in all layered variants of ReS2 can result in substantial losses for the hyperbolic plasmons, as in the case with other known hyperbolic materials, with the exception of MoOCl2. We also note that ReS2 hosts ultraviolet hyperbolic plasmons while ZrSiSe, WTe2, and CuS nanocrystals host infrared plasmons, providing a novel platform for optoelectronics in the ultraviolet range.

Condensed Matter doi: 10.3390/condmat10030039

Authors: Satoru Hayami

We numerically investigate the effect of multi-spin interactions on the stability of skyrmion crystals and other multiple-Q magnetic states, with a particular emphasis on the momentum-resolved bicubic interaction. By performing simulated annealing for an effective spin model that incorporates bilinear, biquadratic, and bicubic interactions on a two-dimensional triangular lattice, we construct the corresponding low-temperature phase diagram. Our results reveal that a positive bicubic interaction stabilizes a skyrmion crystal with a skyrmion number of two, whereas a negative bicubic interaction favors a single-Q spiral state. Moreover, we demonstrate that the stability region of the field-induced skyrmion crystal with the skyrmion number of one is largely enlarged in the presence of a positive bicubic interaction.

Condensed Matter doi: 10.3390/condmat10030038

Authors: Assohoun F. Kraidy Abé S. Yapi Joseph K. Datte Michel Voue Mimoun El Marssi Anthony Ferri Yaovi Gagou

We investigated a novel natural dye-sensitized solar cell (DSSC) utilizing gadolinium ruthenate pyrochlore oxide Gd2Ru2O7 (GRO) as a photoanode and compared its performance to the TiO2-Gd2Ru2O7 (TGRO) combined-layer configuration. The films were fabricated using the spin-coating technique, resulting in spherical grains with an estimated mean diameter of 0.2 µm, as observed via scanning electron microscopy (SEM). This innovative photoactive gadolinium ruthenate pyrochlore oxide demonstrated strong absorption in the visible range and excellent dye adhesion after just one hour of exposure to natural dye. X-ray diffraction confirmed the presence of the pyrochlore phase, where Raman spectroscopy identified various vibration modes characteristic of the pyrochlore structure. Incorporating Gd2Ru2O7 as the photoanode significantly enhanced the overall efficiency of the DSSCs. The device configuration FTO/compact-layer/Gd2Ru2O7/Hibiscus-sabdariffa/electrolyte(I−/I3−)/Pt achieved a high efficiency of 9.65%, an open-circuit voltage (Voc) of approximately 3.82 V, and a current density of 4.35 mA/cm2 for an active surface area of 0.38 cm2. A mesoporous TiO2-based DSSC was fabricated under the same conditions for comparison. Using impedance spectroscopy and cyclic voltammetry measurements, we provided evidence of the mechanism of conductivity and the charge carrier’s contribution or defect contributions in the DSSC cells to explain the obtained Voc value. Through cyclic voltammetry measurements, we highlight the redox activities of hibiscus dye and electrolyte (I−/I3−), which confirmed electrochemical processes in addition to a photovoltaic response. The high and unusual obtained Voc value was also attributed to the presence in the photoanode of active dipoles, the layer thickness, dye concentration, and the nature of the electrolyte.

Condensed Matter doi: 10.3390/condmat10030037

Authors: Bernardo Barbiellini

We present an analytic continuation of the central charge c in two-dimensional conformal field theory (2D CFT), modeled as a Nevanlinna function—an analytic map from the upper half-plane to itself. Motivated by the structure of vacuum energies arising from the quantization of spin-j conformal fields on the circle, we derive a discrete spectrum of central charges c(j)=1+6j(j+1) and extend it continuously via c(z)=1+6z. The Möbius-inverted form f(z)=1−6/z satisfies the conditions of a Nevanlinna function, providing a physically consistent analytic structure that captures both the unitarity of minimal models (c<1) and the continuous spectrum for c≥1. This unified framework highlights the connection between spectral theory, analyticity, and conformal symmetry in quantum field theory.

Condensed Matter doi: 10.3390/condmat10030036

Authors: Paula Riascos Daniel Llamosa Jahaziel Amaya Hansen Murcia

The use of plasmonic nanoparticles for biosensor technology is dependent on nanoparticle size and morphology. This study determined the effect of pH and pressure on synthesizing silver nanoparticle size. In Method 1, a mixture of NaBH4 and sodium citrate was added to a solution of AgNO3 monodispersed by ultrasound energy. In Method 2, the reducer was added to the precursor–dispersant mixture solution. The effect of pH was evaluated by using buffer solutions at pH 4.0, pH 7.0, and pH 10.0 and water as control. To determine the effect of pressure, AgNPs were subjected to 0, 4, and 23 h to 1.75 MPa at 200 °C. AgNPs produced with Method 1 showed a more symmetric SPR and a smaller nanoparticle diameter (±6 nm). The SPR with Method 1 at pH 10.0 produced a higher UV peak with a shift around 20 nm. In the case of the pressure treatment, a shift of approximately 20 nm was observed at all time conditions studied, and a higher AgNP diameter was found in contrast to Method 1. Finally, EDX and Raman analysis confirm the presence of AgNPs and a mild oxidation of these. These results suggest that alkalinity and pressure can affect the diameter of AgNPs.

Condensed Matter doi: 10.3390/condmat10020035

Authors: Satoru Hayami

Magnetic toroidal multipoles have recently emerged as key descriptors of unconventional cross-correlation phenomena in antiferromagnetic systems. Among them, the rank-2 magnetic toroidal quadrupole, which is characterized as a time-reversal-odd polar tensor, has been theoretically associated with a variety of cross-correlation phenomena arising from the time-reversal symmetry breaking. In this study, we investigate the interplay between magnetic toroidal quadrupoles and electric toroidal dipoles in antiferromagnets, with a particular focus on magnetic field-induced ferroaxiality. Through symmetry analysis and microscopic model calculations, we demonstrate that ferroaxiality can be induced by an external magnetic field, depending on both the field direction and the type of the magnetic toroidal quadrupole. We classify all magnetic point groups that possess magnetic toroidal quadrupoles and identify various candidate materials based on the MAGNDATA database. Our findings reveal a route to coupling spin and lattice degrees of freedom via toroidal multipoles.

Condensed Matter doi: 10.3390/condmat10020034

Authors: Pran Nath

The standard models of particle physics and of cosmology have been enormously successful in correlating a large amount of data. However, there are missing pieces and we are still far from what the ultimate model may look like. We give a broad perspective of both the achievements and of the missing pieces and discuss what may lie beyond.

Condensed Matter doi: 10.3390/condmat10020033

Authors: Danijel Djurek Mladen Prester Djuro Drobac Vilko Mandić Damir Pajić

The novel sub-stoichiometric copper oxide CuO0.75 was prepared via the slow oxidation of Cu2O. This compound retains the original crystallographic structure of tenorite CuO, despite the considerable presence of disordered oxygen vacancies. CuO0.75 resembles the mixed valence oxide Cu2+/Cu1+, while the unit cell contains one oxygen vacancy. Performance-wise, the electric resistivity and magnetic susceptibility data follow the Anderson–Mott localization theories. The exponential localization decay length was found to be α−1 = 2.1 nm, in line with modern scaling research. Via cooling, magnetic double-exchange interaction, mediated by oxygen, results in Zener conductivity at T~122 K, which is followed by antiferromagnetic transition at T~51 K. The obtained results indicate that the CuO0.75 compound can be perceived as a showcase material for the demonstration of a new class of high-performance magnetic materials.

Condensed Matter doi: 10.3390/condmat10020032

Authors: Rafael Ferragut

This work reviews the current research directions pursued by collaborations at CERN’s Antiproton Decelerator (AD), with an outlook on future perspectives and challenges in the field. The advancement of precision studies on antimatter builds upon foundational contributions by pioneering researchers, such as Guido Barbiellini Amidei, whose early work on antimatter detection and instrumentation has profoundly influenced the design and methodologies of contemporary experiments at the AD and beyond. This review underscores the lasting impact of these early innovations on ongoing investigations into fundamental symmetries and interactions involving antimatter.

Condensed Matter doi: 10.3390/condmat10020031

Authors: Renee Joselin Sáenz-Hernández Carlos Roberto Santillán-Rodríguez Jesús Salvador Uribe-Chavira José Andrés Matutes-Aquino María Cristina Grijalva-Castillo

This study explores the crystal structure, microstructure and magnetic phase evolution of the AlCoCrFeNi high-entropy alloy (HEA), highlighting its potential for applications requiring tailored magnetic properties across diverse temperatures. Electron microscopy and X-ray diffraction revealed that the as-cast alloy’s microstructure comprises equiaxed grains with branching dendrites, showing compositional variations between interdendritic regions enriched in Al and Ni. Temperature-induced phase transformations were observed above room temperature, transitioning from body centered cubic (BCC) phases (A2 and B2) to a predominant FCC phase at higher temperatures, followed by recrystallization of the A2 phase upon cooling. Magnetization measurements showed a drop near 380 K, suggesting the Curie temperature of BCC phases, a peak at 830 K attributed to optimal magnetic alignment in the FCC phase, and a sharp decline at 950 K marking the transition to a paramagnetic state. Magnetic moment calculations provided insights into magnetic alignment dynamics, while low-temperature analysis highlighted the alloy’s magnetically soft nature, dominated by ferromagnetic contributions from the A2 phase. These findings underscore the strong interdependence of microstructural features and magnetic behavior, offering a foundation for optimizing HEAs for temperature-sensitive scientific and industrial applications.

Condensed Matter doi: 10.3390/condmat10020030

Authors: Guoqiang Zhao Yipeng Cai Kenji M. Kojima Qi Sheng James Beare Graeme Luke Xiang Li Yi Peng Timothy Ziman Kan Zhao Zheng Deng Xiancheng Wang Yongqing Li Gang Su Sadamichi Maekawa Bo Gu Yasutomo J. Uemura Changqing Jin

The investigation of novel diluted magnetic semiconductors (DMSs) provides a promising platform for studying magnetism and transport characteristics, with significant implications for spintronics. DMSs based on BaZn2As2 are particularly noteworthy due to their high Curie temperature (TC) of 260 K, diverse magnetic states, and potential for multilayer heterojunctions. This study investigates the magnetic evolution of carrier doping and spin dynamics in the asperomagnet (Ba,Na)(Zn,Mn)2As2, utilizing a combination of magnetization measurements, ac susceptibility, and muon spin rotation (µSR). Key findings include the following: (1) lower transition temperatures and coercive forces in (Ba,Na)(Zn,Mn)2As2 compared to the ferromagnet (Ba,K)(Zn,Mn)2As2; (2) a dynamic fluctuation peak around the transition temperature observed in both the ac susceptibility and longitudinal field (LF) µSR; and (3) the coexistence of static and dynamic states at low temperatures, exhibiting spin-glass-like characteristics. This study, to the best of our knowledge, may represent the first investigation of asperomagnetic order utilizing µSR techniques. It enhances the understanding of magnetic interactions in BaZn2As2-based systems and provides valuable insights into the exploration of high TC DMSs.

Condensed Matter doi: 10.3390/condmat10020029

Authors: Guangtian Ji Qingqing Yang Kun Zhang Jueming Yang Guixian Ge Wentao Wang

Recently, significant effort has been devoted to enhancing magnetic anisotropy energy (MAE) and the Dzyaloshinskii–Moriya interaction (DMI) in two-dimensional (2D) ferromagnetic materials through various tuning approaches. Among these methods, defect engineering is one of the most effective strategies. However, the influence of these charged defects on the MAE and DMI is unclear. Therefore, we systematically investigate the defect effect on the MAE and DMI of I vacancy-doped (vI-CrI3), 3d-transition-metal-doped (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) (3d-TMi@CrI3), and vI-TM co-doped (3d-TMi@vI-CrI3) monolayer CrI3 using first-principles calculations. Our results indicate that Cr-rich conditions can promote the defect formation of vI-CrI3, 3d-TMi@CrI3, and 3d-TMi@vI-CrI3 systems and demonstrate that 49 types of charged systems are stable. Among these systems, the Cui@vI-CrI3 in the +1 charge state (Cui•@vI-CrI3) system has a smaller defect formation energy, exhibiting a large MAE exceeding 30 meV, and the ratio (D/J) of the antisymmetric magnetic exchange parameter (D) to the Heisenberg exchange parameter (J) reaches 1.04. The large MAE originates from the transition from single-ion anisotropy (SIA) to covalent interaction anisotropy (CIA) due to the coupling variation between the py and px orbitals of I atoms near the Fermi level caused by charge states. The enhancement of the DMI is due to the electrostatic potential differences between the I-top and I-bottom layers, which are conducive to forming stable chiral spin textures. This study provides insight into the defect charge state modulating the magnetism of 2D magnetic materials.

Condensed Matter doi: 10.3390/condmat10020028

Authors: Huanyou Wang Guangqi Xie Yingying Zhan

In this study, the curvature changes of an unintentionally doped GaN end and third quantum well were observed in situ when the annealing times of a GaN buffer layer were 40 s, 50 s and 55 s, respectively. When the annealing time was increased from 40 s to 50 s, the concave curvature of the unintentionally doped GaN end and the third quantum well became smaller. When the annealing time was increased to 55 s, there was no significant change in curvature. These curvature changes are related to the relaxation of the stress in the epitaxial wafer with different annealing times. With the increase in buffer annealing time, the compressive stress and warpage decreased gradually, and the photoluminescence wavelength of the sample became longer. Meanwhile, the standard deviation yield of the dominant wavelength was increased by 5.46%, and the wavelength yield was increased by 19.45% when the annealing time was changed from 40 s to 50 s.

Condensed Matter doi: 10.3390/condmat10020027

Authors: Luis Craco Sabrina Silva Carara

We perform a comprehensive analysis of the correlated electronic structure reconstruction of the ferromagnetic CrSBr van der Waals (vdW) bulk crystal. Using generalized gradient approximation combined with dynamical mean-field theory, we show the minor role played by multi-orbital electron–electron interactions in semiconducting CrSBr. Our study is relevant to understanding the electronic structure within the Cr3+ oxidation state with strongly spin-polarized t2g orbitals and should be applicable to other ferromagnetic vdW materials from bulk down to the low-dimensional limit. This work is relevant for understanding orbital and spin selectivity and its link to the memristor current–voltage characteristic of CrSBr for future neuromorphic computing.

Condensed Matter doi: 10.3390/condmat10020026

Authors: Daniel Alejandro Vázquez-Loredo Ulises Páramo-García Luis Alejandro Macclesh Del Pino-Pérez Nohra Violeta Gallardo-Rivas Ricardo García-Alamilla Diana Lucia Campa-Guevara

Thin films of monomeric species polythiophene (PTh), poly-(3,4-ethylenedioxythiophene) (PEDOT), and the copolymer PTh/PEDOT were prepared through electropolymerization and deposited above fluorine-doped tin oxide (FTO) substrates. The functional groups of the monomeric species (PTh, PEDOT) and polymeric species (PTh/PEDOT) were characterized by Fourier-transform infrared spectroscopy, while morphological properties were evaluated using scanning electron microscopy, optical microscopy, and atomic force microscopy. The analysis showed that monomers films exhibited less material deposition; otherwise, the copolymer PTh/PEDOT showed better deposition on substrate. In addition, the electrochemical characterization showed that the materials that resulted from copolymerization presented an improvement in electrochemical properties relating to monomer properties. The effect of overoxidation of the monomers applied during the electropolymerization process is also known.

Condensed Matter doi: 10.3390/condmat10020025

Authors: Marcello Coreno Massimo Ferrario Augusto Marcelli Francesco Stellato

Exploiting acceleration gradients that are up to three orders of magnitude higher than those achievable using conventional radiofrequency-based devices, plasma-based devices promise a revolution in particle acceleration, enabling particles to reach high energies over much shorter distances than existing accelerators [...]

Condensed Matter doi: 10.3390/condmat10020024

Authors: Jan Kuriplach Rolando Saniz

Judging by the number of downloads and citations, the topics covered by the Special Issue “Rechargeable Batteries Studied Using Advanced Spectroscopic and Computational Techniques I” [...]

Condensed Matter doi: 10.3390/condmat10020023

Authors: Gagik Demirkhanyan Narine Babajanyan Ninel Kokanyan Michel Aillerie Marco Bazzan Edvard Kokanyan

Within the framework of Dexter’s theory, we calculate the energies of the Stark levels of Yb3+-Yb3+ paired centers in lithium niobate doped with Yb3+ ions (LiNbO3:Yb3+) crystal, considering the interaction of optical electrons of ytterbium ions forming the paired center. The calculated Stark level energies are shown to correspond well with the observed cooperative luminescence wavelengths.

Condensed Matter doi: 10.3390/condmat10020022

Authors: Ivan Pelevin Maria Lyange Leonid Fedorenko Stanislav Chernyshikhin Irina Tereshina

In recent years, significant effort was made to make the 3D printing of fully dense rare-earth permanent magnets a reality. Since suitable Nd2Fe14B-based initial powder material became available, additive manufacturing implementation spread widely, which led to many studies being focused on using this material in 3D printing. This study shows the principal possibilities of the synthesis of Nd-Fe-B magnets by means of the laser powder bed fusion technique; moreover, this study shows significant progress in increasing their magnetic properties. This progress was made possible by different approaches, such as 3D-printing process optimization, the addition of a second phase (a low-melting eutectic) into the initial powder, the tuning of the main phase’s composition, and exploring different scanning strategies. However, the current level of material magnetic properties obtained via laser powder bed fusion is still far from that of magnets produced by using conventional powder metallurgy methods. The present review aims to capture the current state-of-the-art trials and highlight the main challenges.

Condensed Matter doi: 10.3390/condmat10020021

Authors: I. V. Solovyev

Basic principles of ferroelectric activity induced by the noncollinear alignment of spins are reviewed. There is a fundamental reason why the inversion symmetry can be broken by certain magnetic order. This situation occurs when the magnetic order simultaneously involves ferromagnetic (F) and antiferromagnetic (A) counterparts, transforming under the spatial inversion I and time reversal T as IF=F and ITA=A, respectively. The incompatibility of these two conditions results in breaking the inversion symmetry, which manifests itself in the electric polarization P→. The noncollinear alignment of spins is one of examples of such coexistence of F and A. This coexistence principle imposes a constraint on possible dependencies of P→ on the directions of spins, which can include only “antisymmetric coupling” in the bond, P→ij·[ei×ej], and “single-ion anisotropy”, ei· Π→ ei. Microscopically, P→ij can be evaluated in the framework of superexchange theory. For the single Kramers doublet, this theory yields P→ij∼r→ij0, where r→ij0 is the spin-dependent part of the position operator induced by the relativistic spin-orbit coupling. r→ij0 remains invariant under spatial inversion, providing the microscopic reason why noncollinear alignment of spins can induce P→ even in centrosymmetric crystals. The symmetry properties of r→ij0 can be rationalized from the viewpoint of symmetry of Kramers states. Particularly, the commonly used Katsura–Nagaosa–Balatsky (KNB) rule P→∝ϵ→ji×[ei×ej] (ϵ→ji being the direction of the bond ij) can be justified only for relatively high symmetry of the bonds. The single-ion anisotropy vanishes for the spin 12 or if magnetic ions are located in inversion centers, thus severely restricting the applicability of this microscopic mechanism. The properties of multiferroic materials are reconsidered from the viewpoint of these principles. A particular attention is paid to complications caused by possible deviations from the KNB rule.

Condensed Matter doi: 10.3390/condmat10020020

Authors: Maria Cristina Diamantini

Magnetic monopoles, though elusive as elementary particles, emerge as quantum excitations in granular quantum materials. Under certain conditions, they can undergo Bose condensation, leading to the formation of a novel state of matter known as the superinsulator. In this state, charge carriers, Cooper pairs and anti-Cooper pairs, are bound together by an electric flux string, forming neutral electric pions. This confinement mechanism results in an infinite resistance that persists even at finite temperatures. Superinsulators behave, thus, as dual superconductors.

Condensed Matter doi: 10.3390/condmat10010019

Authors: Kanat Tolubayev Bakhyt Zhautikov Nikolay Zobnin Guldana Dairbekova Saule Kabiyeva

In this study, the effects of specific power (1–100 W/cm2), operating pressure (0.5–3.0 Pa), and voltage frequency (20–500 kHz) on film growth kinetics, morphology, and silicon entrainment were investigated to optimize magnetron sputtering for producing thin silicon films suitable for lithium-ion battery anodes. Silicon films were deposited on copper substrates using the Caroline D12C system. The film thickness and morphology were determined using scanning electron microscopy and atomic force microscopy. It was found that the porosity of the films increases with increasing pressure in the working chamber. It was found that the film morphology is non-uniform up to a thickness of 100–150 nm. After that, the film thickness becomes uniform over the entire substrate surface, and the deposition rate increases sharply, i.e., an induction period is observed. The induction period duration decreases with increasing voltage power and frequency. At the same time, silicon removal increases. Frequency has a greater effect on both parameters. The paper specifies a strategy for the technical and economic optimization of the magnetron sputtering process, which determines a compromise between the positive effect of increasing productivity and the negative effect of silicon removal.

Condensed Matter doi: 10.3390/condmat10010018

Authors: Luis Craco

Based on DFT + DMFT, we investigate the orbital-nematic and s-wave superconducting states of a hole-doped NdNiO2 superconductor. We emphasize the role played by the interorbital proximity effect in determining the orbital-selective electronic state both in the normal and superconducting phases. Specifically, we show how orbital-nematic plus s-wave pairing symmetry acting on the xz orbital might have pronounced effects on proximitized non-superconducting Ni-3d orbitals due to many-particle electron–electron interactions. This work represents a step forward in understanding the emergence of two-fluid superconductivity (with superconducting xz and non-superconducting xy,yz,x2−y2,3z2−r2 channels) in hole-doped NdNiO2 superconductors.

Condensed Matter doi: 10.3390/condmat10010017

Authors: Giovanni Alberto Ummarino Alessio Zaccone

It is known that noble metals such as gold, silver and copper are not superconductors; this is also true for magnesium. This is due to the weakness of the electron–phonon interaction, which makes them excellent conductors but not superconductors. As has recently been shown for gold, silver and copper, and even for magnesium, it is possible that in very particular situations, superconductivity may occur. Quantum confinement in thin films has been consistently shown to induce a significant enhancement of the superconducting critical temperature in several superconductors. It is therefore an important fundamental question whether ultra-thin film confinement may induce observable superconductivity in non-superconducting metals such as magnesium. We study this problem using a generalization, in the Eliashberg framework, of a BCS theory of superconductivity in good metals under thin-film confinement. By numerically solving these new Eliashberg-type equations, we find the dependence of the superconducting critical temperature on the film thickness, L. This parameter-free theory predicts superconductivity in very thin magnesium films. We demonstrate that this is a fine-tuning problem where the thickness must assume a very precise value, close to half a nanometer.

Condensed Matter doi: 10.3390/condmat10010016

Authors: Fabrizio Napolitano Alessandro Scordo

High-Precision X-ray Measurements 2023 is a Special Issue of the journal Condensed Matter enclosing the scientific content of the 2023 High-Precision X-ray Measurements (HPXRM) conference [...]

Condensed Matter doi: 10.3390/condmat10010015

Authors: Irene Gaiardoni Mattia Trama Alfonso Maiellaro Claudio Guarcello Francesco Romeo Roberta Citro

We investigate spin-to-charge conversion via the Edelstein effect in a 2D Rashba electron gas using the semiclassical Boltzmann approach. We analyze the magnetization arising from the direct Edelstein effect, taking into account an anisotropic Rashba model. We study how this effect depends on the effective masses and Rashba spin–orbit coupling parameters, extracting analytical expressions for the high electronic density regime. Indeed, it is possible to manipulate the anisotropy introduced into the system through these parameters to achieve a boost in the Edelstein response compared to the isotropic Rashba model. We also discuss the theoretical framework to study the inverse Edelstein effect and calculate self-consistently the electric current induced by the proximity of the system to a ferromagnet. These results provide insights into the role of Rashba spin–orbit coupling and anisotropic effects in spin–charge conversion phenomena.

Condensed Matter doi: 10.3390/condmat10010014

Authors: Fabián G. Medina Cuy Fabrizio Dolcini

A current flowing through a one-dimensional Kitaev chain induces a spatial modulation in its superconducting pairing, characterized by a wavevector Q, which is known to induce two types of topological phase transitions: one is the customary band topology transition between gapped phases, while the other is a Lifshitz transition related to the Fermi surface topology and leading to a gapless superconducting phase. We investigate the behavior of the electron density ρ and the compressibility κ across the two types of transitions, as a function of the model parameters. We find that the behavior of ρ as a function of Q and chemical potential μ enables one to infer the ground state phase diagram. Moreover, the analysis of the compressibility κ as a function of μ enables one to distinguish the two transitions: While κ exhibits a symmetric divergence across the band topology transition, it displays an asymmetric jump across the Lifshitz transition.

Condensed Matter doi: 10.3390/condmat10010013

Authors: Taimo Priinits Artjom Vargunin Aleksandr Liivand

The present report focuses on the close interplay between condensed matter physics and solid-state chemistry in Nb-based binary intermetallic compounds. Over the recent four decades, these materials have been widely used in the development of a number of superconducting applications and various superconducting devices, including non-standard engineering solutions in the design of large magnets. However, since the 1980s, when it became apparent that the mechanical and superior superconducting properties of ordered intermetallic alloys such as Nb3Sn were largely due to their unique structural features, much of the research interest in the science of superconducting intermetallic alloys has been redirected to the development of necessary engineering applications in high magnetic field technology. Accordingly, the important role of crystal chemistry in understanding the fundamental aspects of the material properties of the Nb3Sn family of intermetallics has not been extensively explored. In this paper, we try to fill this gap by investigating the relationships between composition, microstructure and properties, highlighting their relevance to technological applications. Our goal is to combine aspects of crystal chemistry with physical and material application issues. We shed light on the atomic assembly mechanisms and processes in terms of changes in the chemical environment, lattice structure, crystallization pathway, and macroscale phase textures, which can help in interpreting and explaining the prospects and limitations of the superconducting properties of Nb3Sn. In the context of past and present prospects and limitations, we briefly overview most important technological applications and discuss the various inter-relations between superconductivity and structural properties of Nb-based A-15 intermetallic alloys. We argue that these inter-relations can be used to find Nb-based superconductors with more superior properties and stronger technological usability.

Condensed Matter doi: 10.3390/condmat10010012

Authors: Melissa Alzate Banguero Sayan Basak Nicolas Raymond Forrest Simmons Pavel Salev Ivan K. Schuller Lionel Aigouy Erica W. Carlson Alexandre Zimmers

Quantum materials have tremendous potential for disruptive applications. However, scaling devices down has been challenging due to electronic inhomogeneities in many of these materials. Understanding and controlling these electronic patterns on a local scale has thus become crucial to further new applications. To address this issue, we have developed a new optical microscopy method that allows for the precise quasi-continuous filming of the insulator-to-metal transition in VO­2 with fine temperature steps. This enables us to track metal and insulator domains over thousands of images and quantify, for the first time, the local hysteresis properties of VO­2 thin films. The analysis of the maps has allowed us to quantify cycle-to-cycle reproducibility of the local transitions and reveals a positive correlation between the local insulator–metal transition temperatures T­c and the local hysteresis widths ΔTc. These maps also enable the optical selection of regions of high or low transition temperature in combination with large or nearly absent local hysteresis. These maps pave the way to understand and use stochasticity to advantage in these materials by picking on-demand transition properties, allowing the scaling down of devices such as optical switches, infrared microbolometers and spiking neural networks.

Condensed Matter doi: 10.3390/condmat10010011

Authors: Natasha Kirova Serguei Brazovskii

Phase transformations induced by short optical pulses are mainstream in studies on the dynamics of cooperative electronic states. We present a semiphenomenological modeling of spatiotemporal effects expected when optical excitons are intricate with the order parameter such as in, e.g., organic compounds with neutral-ionic ferroelectric phase transitions. A conceptual complication appears here, where both the excitation and the ground state ordering are built from the intermolecular electronic transfer. To describe both thermodynamic and dynamic effects on the same root, we adopt, for the phase transition, a view of the excitonic insulator—a hypothetical phase of a semiconductor that appears if the exciton energy becomes negative. After the initial pumping pulse, a quasi-condensate of excitons can appear as a macroscopic quantum state that then evolves, while interacting with other degrees of freedom which are prone to an instability. The self-trapping of excitons enhances their density, which can locally surpass a critical value to trigger the phase transformation. The system is stratified in domains that evolve through dynamical phase transitions and may persist even after the initiating excitons have recombined.

Condensed Matter doi: 10.3390/condmat10010010

Authors: David Valenzuela Alfredo Raya Juan D. García-Muñoz

We explore the equivalence between the low-energy dynamics of strained graphene and a quantum mechanical framework for the 2D Dirac equation in flat space with a deformed momentum operator. By considering some common forms of the anisotropic Fermi velocity tensor emerging from the elasticity theory, we associate such tensor forms with a deformation of the momentum operator. We first explore the bound states of charge carriers in a background uniform magnetic field in this framework and quantify the impact of strain in the energy spectrum. Then, we use a quadrature algebra formula as a mathematical tool to analyze the impact of the deformation attached to the momentum operator and identify physical consequences of such deformation in terms of energy modifications due to the applied strain.

Condensed Matter doi: 10.3390/condmat10010009

Authors: Ivan Kupčić Patrik Papac

We studied relaxation processes in heavily doped two-dimensional Dirac systems associated with electron scattering by acoustic and optical phonons and by static disorder. The frequency dependence of the real and imaginary parts of the relaxation function is calculated for different temperatures. The two-component low-frequency dynamical conductivity is found to be strongly dependent on temperature. At low temperatures, the imaginary part of the zero-frequency relaxation function and the DC resistivity are characterized by the scaling law aTx with the exponent x between 2.5 and 3.

Condensed Matter doi: 10.3390/condmat10010008

Authors: Vasily Milyutin Irina Gervasyeva Azambek Kalonov Denis Shishkin Denis Davydov Liudmila Stashkova

FeGa alloys with small additions of rare-earth elements surpass binary alloys in magnetostriction and plasticity. For this reason, they are considered promising magnetostrictive materials for various electrical engineering applications. The alloy (Fe81Ga19)99.8Ce0.2 was prepared and investigated in this work. It was found that in the cast state, it has a magnetostriction of 3/2 λ about 100 ppm, saturation magnetization of 150 emu/g, tensile strength of about 300 MPa, and fracture strain of 3%. The microstructure, crystallographic texture, and behavior when heated of the alloy were investigated. Then the ingot was subjected to forging and hot rolling with a deformation degree of 90% at 1000 °C. The structure and mechanical properties of samples cut from a hot rolling sheet were studied. Their tensile strength and fracture strain increase compared to cast state up to 600 MPa and 4% correspondingly.

Condensed Matter doi: 10.3390/condmat10010007

Authors: Filippo Pascucci Sara Conti David Neilson Andrea Perali Jacques Tempere

We propose a new way to establish the existence of a superfluid phase in an exciton bilayer system by exploiting the properties of its collective modes. We focus on the density collective modes and treat them within Random Phase Approximation. By comparing results for the normal and superfluid states, we are able to identify unambiguous fingerprints of the exciton superfluid phase. We compare the collective modes of the exciton system and cold atom systems, and we discuss the collective modes of the exciton superfluid order parameter.

Condensed Matter doi: 10.3390/condmat10010006

Authors: Ya-Chih Cheng Sanjaya Brahma Sean Wu Jow-Lay Huang Alex C. H. Lee

Zinc oxide (ZnO) exhibits piezoelectric properties due to its asymmetric structure, making it suitable for piezoelectric devices. This experiment deposited Fe-doped ZnO films on silicon substrates using a dual-target magnetron co-sputtering system. The films achieved a high c-axis orientation, and the piezoelectric coefficient of the film reached its optimal value of 44.35 pC/N when doped with 0.5 at% of Fe. This value is approximately three times that of undoped ZnO films with a piezoelectric coefficient of 13.04 pC/N. The study utilized a diffractometer, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy to evaluate the crystal structure evolution of the zinc oxide films and employed X-ray photoelectron spectroscopy to assess the valence state of the Fe ions.

Condensed Matter doi: 10.3390/condmat10010005

Authors: Sudip Sinha Subhasis Sinha

We introduce the concept of ergodicity and explore its deviation caused by quantum scars in an isolated quantum system, employing a pedagogical approach based on a toy model. Quantum scars, originally identified as traces of classically unstable orbits in certain wavefunctions of chaotic systems, have recently regained interest for their role in non-ergodic dynamics, as they retain memory of their initial states. We elucidate these features of quantum scars within the same framework of this toy model. The integrable part of the model consists of two large spins, with a classical counterpart, which we combine with a random matrix to induce ergodic behavior. Scarred states can be selectively generated from the integrable spin Hamiltonian by protecting them from the ergodic states using a projector method. Deformed projectors mimic the ‘quantum leakage’ of scarred states, enabling tunable mixing with ergodic states and thereby controlling the degree of scarring. In this simple model, we investigate various properties of quantum scarring and shed light on different aspects of many-body quantum scars observed in more complex quantum systems. Notably, the underlying classicality can be revealed through the entanglement spectrum and the dynamics of ‘out-of-time-ordered correlators’.

Condensed Matter doi: 10.3390/condmat10010004

Authors: Roberto Raimondi Thierry Valet

The spin Hall effect for the model Hamiltonian of graphene with Rashba spin–orbit coupling is analyzed by means of a recently derived quantum kinetic theory of the linear response for multi-band electron systems. The latter expresses the interband part of the density matrix in terms of the intraband occupation numbers, which can be obtained as solutions of a Boltzmann transport equation. The analysis, which, in the case of the model here considered, can be carried out in a completely analytical way, thus provides an effective pedagogical illustration of the general theory. While our results agree with those previously obtained with alternative approaches for the same model, our comparatively simpler and more physically transparent derivation illustrates the advantages of our formalism when dealing with non trivial multi-band Hamiltonians.

Condensed Matter doi: 10.3390/condmat10010003

Authors: Anouar Moustaj Julius Krebbekx Cristiane Morais Smith

Multilevel charge pumping is a feature that was recently observed in quasiperiodic systems. In this work, we show that it is more generic and appears in different aperiodic systems. Additionally, we show that for aperiodic systems admitting arbitrarily long palindromic factors, the charge pumping protocol connects two topologically distinct insulating phases. This confirms the existence of topological phases in aperiodic systems whenever their finite-size realizations admit inversion symmetry. These phases are characterized by an anomalous edge response resulting from the bulk–boundary correspondence. We show that these signatures are all present in various chains, each representing a different class of structural aperiodicity: the Fibonacci quasicrystal, the Tribonacci quasicrystal, and the Thue–Morse chain. More specifically, we calculate three quantities: the Berry phase of the periodic approximation of the finite-size systems, the polarization response to an infinitesimal static and constant electric field in systems with open boundary conditions, and the degeneracy of the entanglement spectrum. We find that all of them provide signatures of a topologically nontrivial phase.

Condensed Matter doi: 10.3390/condmat10010002

Authors: Edine Silva Mucio A. Continentino

In this paper, we study the appearance of topological p-wave superconductivity of the type S=1, Sz=0 in a layer of adatoms. This unconventional superconductivity arises due to an anti-symmetric hybridization between the orbitals of the adatoms and those of the atoms in the superconducting BCS substrate. This two-dimensional system is topologically non-trivial only in the absence of a magnetic field and belongs to class DIII of the Altland–Zirnbauer classification. We obtain the Pfaffian that characterizes the topological phases of the system and its phase diagram. We discuss the differences between the two-dimensional case and a chain with the same type of superconductivity.

Condensed Matter doi: 10.3390/condmat10010001

Authors: Ke Wang Junchao Xu Hironaru Murakami Hiroyasu Yamahara Munetoshi Seki Hitoshi Tabata Masayoshi Tonouchi

Temperature dependence of the lowest frequency transverse optical phonon (TO1) in a single crystal Substituted Gadolinium Gallium Garnet (SGGG, (001)) was studied using terahertz time-domain spectroscopy at temperatures between 80 K and 500 K. The complex dielectric constants were calculated from the optical constants fitting with the Lorentz oscillator model. The results show that the TO1 phonon of SGGG is at 2.5 THz at room temperature, the frequency of the TO1 phonon slightly decreases, and the dumping factor clearly increases with increasing temperature. Additionally, our results demonstrate that even a small substitution can induce a phonon shift, leading to higher absorption and causing a slight degradation in thermal stability. Our work is expected to support the development of magneto-optical and spintronic devices.

Condensed Matter doi: 10.3390/condmat9040056

Authors: Annette Bussmann-Holder Hugo Keller

Early on, oxides were ruled out from superconductivity, since they are typically large-band-gap insulators. Nevertheless, a rather small number of them were found to be superconducting, with transition temperatures up to 14 K and a remarkably low carrier density. This was the starting point of K. Alex Müller (KAM) becoming interested in superconductivity in oxides. Step by step, he advanced the research on oxides and finally discovered, together with J. Georg Bednorz, high-temperature superconductivity (HTSC) in the perovskite-type compound Ba-La-Cu-O. Even though he was inspired by specific and clear ideas in his search, he added new impact in the understanding of HTSC for many years after receipt of the Nobel prize for this discovery.

Condensed Matter doi: 10.3390/condmat9040055

Authors: M. Victoria Ale Crivillero Priscila F. S. Rosa Zachary Fisk Jens Müller Pedro Schlottmann Steffen Wirth

While SmB6 attracts attention as a possible topological Kondo insulator, EuB6 is known to host magnetic polarons that give rise to large magnetoresistive effects above its ferromagnetic order transition. Here, we investigate single crystals of Sm1−xEuxB6 by magnetic and magnetotransport measurements to explore a possible interplay of these two intriguing phenomena, with a focus on the Eu-rich substitutions. Sm0.01Eu0.99B6 exhibits generally similar behavior as EuB6. Interestingly, Sm0.05Eu0.95B6 combines a global antiferromagnetic order with local polaron formation. A pronounced hysteresis is found in the magnetoresistance of Sm0.1Eu0.9B6 at low temperature (T= 1.9 K) and applied magnetic fields between 2.3 and 3.6 T. The latter is in agreement with a phenomenological model that predicts the stabilization of ferromagnetic polarons with an increasing magnetic field within materials with a global antiferromagnetic order.

Condensed Matter doi: 10.3390/condmat9040054

Authors: A. G. Marinopoulos

Despite the fact that yttria-stabilized zirconia has been studied experimentally by optical and electron energy-loss spectroscopies, a first-principles theoretical interpretation of the dielectric response and electronic excitations is still lacking. The present study reports calculations of the complex dielectric function, reflectivity spectrum and electron energy-loss function of two ordered yttria–zirconia compounds: Zr6Y2O15 and Zr3Y4O12. The adopted methodology is based on linear-response theory with a semilocal density functional and the random-phase approximation including local-field effects. Comparisons with existing experimental data show an acceptable agreement showcasing how the different yttria content affects dielectric properties and spectra lineshapes. Strong discrepancies with experimental data are mainly confined to the low-energy part of the optical spectra and concern both the peak positions and the lineshape intensities. The onset of the optical absorption is considerably underestimated from the calculations owing to the well-known deficiency of semilocal density functionals to describe the quasiparticle band gaps. The energy-loss spectra, instead, are reproduced extremely well provided that local-field effects are included in the response functions. These effects are particularly important for the description of the semicore Zr–4p and Y–4p excitations, which dominate for higher energies (>30 eV) in the valence region.

Condensed Matter doi: 10.3390/condmat9040053

Authors: Nicholay S. Tonchev Daniel Dantchev

For studying the finite-size behavior of the Ising model under different boundary conditions, we propose an alternative to the standard transfer matrix technique approach based on Abelès theorem and Chebyshev polynomials. Using it, one can easily reproduce the known results for periodic boundary conditions concerning the Lee–Yang zeros, the exact position-space renormalization-group transformation, etc., and can extend them by deriving new results for antiperiodic boundary conditions. Note that in the latter case, one has a nontrivial order parameter profile, which we also calculate, where the average value of a given spin depends on the distance from the seam with the opposite bond in the system. It is interesting to note that under both boundary conditions, the one-dimensional case exhibits Schottky anomaly.

Condensed Matter doi: 10.3390/condmat9040052

Authors: Giovanni Mirarchi Sergio Caprara

Inspired by the phenomenology of high-critical-temperature superconducting cuprates, we investigate the effect of an anisotropic scattering rate on the magnetoresistance of a metal, relying on Chambers’ solution to the Boltzmann equation. We find that if the scattering rate is enhanced near points of the Fermi surface with a locally higher density of states, an extended regime is found where the magnetoresistance varies linearly with the magnetic field. We then apply our results to fit the experimental magnetoresistance of La1.6−xNd0.4SrxCuO4 and speculate about the possible source of anisotropic scattering.

Condensed Matter doi: 10.3390/condmat9040051

Authors: Giorgio Benedek Joseph R. Manson Salvador Miret-Artés Detlef Schmicker Jan Peter Toennies

Previously, helium atom scattering (HAS) has been shown to probe the electron–phonon interaction at conducting crystal surfaces via the temperature dependence of the specular peak intensity. This method is now extended to non-stoichiometric superconductors. The electron–phonon interaction, as expressed by the mass-enhancement factor λ, is derived from the temperature dependence of the diffuse elastic scattering intensity, which specifically depends on the non-stoichiometric component responsible for superconductivity. The measured value of the mass-enhancement factor for Bi2Sr2CaCu2O8+δ at the optimal doping δ = 0.16 is λ = 0.55 ± 0.08 is in good agreement with values of λ recently estimated with other methods. This also confirms the relevant role of electron–phonon interaction in high-temperature non-stoichiometric cuprate superconductors.

Condensed Matter doi: 10.3390/condmat9040050

Authors: Jeferson Danilo L. Silva Alessandra N. Braga Wagner P. Pires Danilo T. Alves Van Sérgio Alves

In a recent work, it was demonstrated within the framework of Pseudo Quantum Electro-dynamics (PQED) at zero temperature that the logarithmic renormalization of the Fermi velocity in a graphene sheet is inhibited by the presence of a single parallel conducting plate. In the present study, aiming for a more general and realistic approach, we explore the renormalization of the Fermi velocity and mass (band gap) in a two-dimensional system influenced by a conducting plate at finite temperature, also in the context of PQED. Our findings refine previous results in the literature and provide valuable insights for future investigations on the effects of external conditions within PQED.

Condensed Matter doi: 10.3390/condmat9040049

Authors: Brayan Stick Betin Bohorquez Indry Milena Saavedra Gaona Carlos Arturo Parra Vargas Karina Vargas-Sánchez Jahaziel Amaya Mónica Losada-Barragán Javier Rincón Daniel Llamosa Pérez

The present work proposes a method for the synthesis of a nanoparticle with a superparamagnetic Fe3O4 core coated with SiO2-NH2 by ultrasound-assisted coprecipitation. Additionally, the nanoparticle is functionalized with a microinflammation biomarker peptide, and its effects on the viability of monkey kidney endothelial cells and the Vero cell line were evaluated. The main physicochemical properties of the nanoparticles were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), a vibrating sample magnetometer (VSM), a field emission scanning electron, Scanning Electron Microscopy (SEM), and High-Resolution Transmission Electron Microscopy (HR-TEM). The results showed that the nanoparticles are spherical, with sizes smaller than 10 nm, with high thermal stability and superparamagnetic properties. They also demonstrated cell viability rates exceeding 85% through Magnetic Resonance Imaging (MRI). The results indicate the potential of these nanoparticles to be used as a contrast agent in magnetic resonance to detect mild brain lesions.

Condensed Matter doi: 10.3390/condmat9040048

Authors: Mihail D. Croitoru Alexander I. Buzdin

The Inverse Faraday Effect (IFE) is a phenomenon that enables non-thermal magnetization in various types of materials through the interaction with circularly polarized light. This study investigates the impact of single defects on the ability of circularly polarized radiation to switch between distinct superconducting current states, when the magnetic flux through a superconducting ring equals half the quantum flux, Φ0/2. Using both analytical methods within the standard Ginzburg–Landau theory and numerical simulations based on the stochastic time-dependent Ginzburg–Landau approach, we demonstrate that while circularly polarized light can effectively switch between current-carrying superconducting states, the presence of a single defect significantly affects this switching mechanism. We establish critical temperature conditions above which the switching effect completely disappears, offering insights into the limitations imposed by a single defect on the dynamics of light-induced IFE-based magnetization in superconductors.

Condensed Matter doi: 10.3390/condmat9040047

Authors: Hocine Menana

An integrodifferential model formulated in terms of the electric vector potential is developed for the 3D numerical modeling of the electromagnetic field in superconducting bulks, for AC losses evaluation. The Newton Raphson method is applied to accelerate the convergence. The model is validated on a benchmark. The comparison results show the accuracy of the model and its performances in terms of computation time compared to classical approaches.

Condensed Matter doi: 10.3390/condmat9040046

Authors: Miroslav D. Dramićanin Abdullah N. Alodhayb Aleksandar Ćirić

Over the past three decades, luminescence thermometry has gained significant attention among researchers and practitioners. The method has progressed in terms of utilizing temperature-sensitive luminescent materials, obtaining temperature read-outs from luminescence, developing applications, and improving performance. This paper reviews and critically analyzes routes for improving luminescence thermometry performance, in particular the sensitivity, accuracy, and precision of the method. These include the use of highly temperature-sensitive probes, temperature read-outs from luminescence with improved sensitivity, multiparameter temperature-reading methods, the applications of principal component analysis and artificial neural networks, and sensor fusion.

Condensed Matter doi: 10.3390/condmat9040045

Authors: Myung-Hwan Whangbo Hyun-Joo Koo Reinhard K. Kremer Alexander N. Vasiliev

To search for a conceptual picture describing the magnetization plateau phenomenon, we surveyed the crystal structures and the spin lattices of those magnets exhibiting plateaus in their magnetization vs. magnetic field curves by probing the three questions: (a) why only certain magnets exhibit magnetization plateaus, (b) why there occur several different types of magnetization plateaus, and (c) what controls the widths of magnetization plateaus. We show that the answers to these questions lie in how the magnets under field absorb Zeeman energy, hence changing their magnetic structures. The magnetic structure of a magnet insulator is commonly described in terms of its spin lattice, which requires the determination of the spin exchanges’ nonnegligible strengths between the magnetic ions. Our work strongly suggests that a magnet under the magnetic field partitions its spin lattice into antiferromagnetic (AFM) or ferrimagnetic fragments by breaking its weak magnetic bonds. Our supposition of the field-induced partitioning of spin lattices into magnetic fragments is supported by the anisotropic magnetization plateaus of Ising magnets and by the highly anisotropic width of the 1/3-magnetization plateau in azurite. The answers to the three questions (a)–(c) emerge naturally by analyzing how these fragments are formed under the magnetic field.

Condensed Matter doi: 10.3390/condmat9040044

Authors: Macauley Curtis Martin Gradhand James F. Annett

Uniaxial strain in the (100) direction has the effect of increasing the superconducting Tc in Sr2RuO4 from 1.5 K to over 3 K. The enhanced Tc corresponds to a Lifshitz transition in the Fermi surface topology of this unconventional superconductor. We model this using a simple two-dimensional one-band model for the γ sheet of the Fermi surface. This reproduces the experimental Tc results well if we assume a dx2−y2 singlet pairing state. On the other hand, the triplet state px+ipy does not show any distinct peaks in Tc associated with the Lifshitz transition. A mixed symmetry state pairing of the form d+ig can both describe the Tc changes and show a distinct transition temperature for time-reversal symmetry breaking (TRSB).

Condensed Matter doi: 10.3390/condmat9040043

Authors: Gaetano Campi Gennady Logvenov Sergio Caprara Antonio Valletta Antonio Bianconi

Recently, the quest for high-Tc superconductors has evolved from the trial-and-error methodology to the growth of nanostructured artificial high-Tc superlattices (AHTSs) with tailor-made superconducting functional properties by quantum design. Here, we report the growth by molecular beam epitaxy (MBE) of a superlattice of Mott insulator metal interfaces (MIMIs) made of nanoscale superconducting layers of quantum confined-space charge in the Mott insulator La2CuO4 (LCO), with thickness L intercalated by normal metal La1.55Sr0.45CuO4 (LSCO) with period d. The critical temperature shows the superconducting dome with Tc as a function of the geometrical parameter L/d showing the maximum at the magic ratio L/d = 2/3 where the Fano–Feshbach resonance enhances the superconducting critical temperature. The normal state transport data of the samples at the top of the superconducting dome exhibit Planckian T-linear resistivity. For L/d > 2/3 and L/d < 2/3, the heterostructures show a resistance following Kondo universal scaling predicted by the numerical renormalization group theory for MIMI nanoscale heterostructures. We show that the Kondo temperature, TK, and the Kondo scattering amplitude, R0K, vanish at L/d = 2/3, while TK and R0K increase at both sides of the superconducting dome, indicating that the T-linear resistance regime competes with the Kondo proximity effect in the normal phase of MIMIs.

Condensed Matter doi: 10.3390/condmat9040042

Authors: L. Craco

The emergence of a charge density wave (CDW) in transition-metal dichalcogenides opens up a route to charge order, followed by superconductivity at low temperatures. A key question here concerns how many particle electron–electron interations govern the low-energy electronic structure in the normal and CDW states. Using dynamical mean-field theory, we explore the many-body properties of an extended, two-band Hubbard model applicable to 2H-TaSe2. We reveal the electronic structure reconstruction in the normal and CDW states driven by two-band dynamical correlations. Our results demonstrate a remarkable renormalization of the Ta-5d bands crossing the Fermi level, showing a continuous reduction in the CDW gap up to an incomplete gapping, followed by a CDW to a CDW–Mott phase transition pertinent to strongly correlated transition-metal dichalcogenides.