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Condensed Matter

Condensed Matter is an international, peer-reviewed, open access journal on the physics of condensed matter published quarterly online by MDPI.

Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
High Visibility: indexed within Scopus, ESCI (Web of Science), Inspec, CAPlus / SciFinder, and other databases.
Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 20.1 days after submission; acceptance to publication is undertaken in 2.7 days (median values for papers published in this journal in the first half of 2025).
Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.

Impact Factor: 1.5 (2024); 5-Year Impact Factor: 1.5 (2024)

Imprint Information Journal Flyer Open Access ISSN: 2410-3896

Latest Articles

11 pages, 962 KiB

Open AccessArticle

Possible Realization of Hyperbolic Plasmons in Few-Layered Rhenium Disulfide

by Ravi Kiran, Dimitar Pashov, Mark van Schilfgaarde, Mikhail I. Katsnelson, Arghya Taraphder and Swagata Acharya

Condens. Matter 2025, 10(3), 40; https://doi.org/10.3390/condmat10030040 - 19 Jul 2025

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 [...] Read more.

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

{ReS}_{2}

, and our theory shows that

{ReS}_{2}

can host hyperbolic plasmons in the ultraviolet frequency range. The operating frequency range of the hyperbolic plasmons can be tuned with the number of

{ReS}_{2}

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. Full article

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16 pages, 1799 KiB

Open AccessArticle

Skyrmion Crystal in Bilinear–Biquadratic–Bicubic Model on a Centrosymmetric Triangular Lattice

by Satoru Hayami

Condens. Matter 2025, 10(3), 39; https://doi.org/10.3390/condmat10030039 - 18 Jul 2025

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 [...] Read more.

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. Full article

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24 pages, 7332 KiB

Open AccessArticle

High-Performance Natural Dye-Sensitized Solar Cells Employing a New Semiconductor: Gd₂Ru₂O₇ Pyrochlore Oxide

by Assohoun F. Kraidy, Abé S. Yapi, Joseph K. Datte, Michel Voue, Mimoun El Marssi, Anthony Ferri and Yaovi Gagou

Condens. Matter 2025, 10(3), 38; https://doi.org/10.3390/condmat10030038 - 14 Jul 2025

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 [...] Read more.

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. Full article

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5 pages, 197 KiB

Open AccessCommunication

Nevanlinna Analytical Continuation of the Central Charge in 2D Conformal Field Theory

by Bernardo Barbiellini

Condens. Matter 2025, 10(3), 37; https://doi.org/10.3390/condmat10030037 - 8 Jul 2025

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- [...] Read more.

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 + 6 j (j + 1)

and extend it continuously via

c (z) = 1 + 6 z

. 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 \geq 1

. This unified framework highlights the connection between spectral theory, analyticity, and conformal symmetry in quantum field theory. Full article

(This article belongs to the Special Issue The Universe Observed With Particle Detectors: Celebrating the Scientific Legacy of Prof. Guido Barbiellini Amidei)

18 pages, 1546 KiB

Open AccessArticle

Ultrasound-Assisted Synthesis for the Control of Silver Nanoparticle Size: A Preliminary Study on the Influence of Pressure and pH

by Paula Riascos, Daniel Llamosa, Jahaziel Amaya and Hansen Murcia

Condens. Matter 2025, 10(3), 36; https://doi.org/10.3390/condmat10030036 - 7 Jul 2025

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 [...] Read more.

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. Full article

(This article belongs to the Section Physics of Materials)

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15 pages, 803 KiB

Open AccessArticle

Field-Induced Ferroaxiality in Antiferromagnets with Magnetic Toroidal Quadrupole

by Satoru Hayami

Condens. Matter 2025, 10(2), 35; https://doi.org/10.3390/condmat10020035 - 14 Jun 2025

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 [...] Read more.

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. Full article

(This article belongs to the Section Magnetism)

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8 pages, 227 KiB

Open AccessPerspective

The Standard Model of Particle Physics and What Lies Beyond: A View from the Bridge

by Pran Nath

Condens. Matter 2025, 10(2), 34; https://doi.org/10.3390/condmat10020034 - 13 Jun 2025

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue The Universe Observed With Particle Detectors: Celebrating the Scientific Legacy of Prof. Guido Barbiellini Amidei)

8 pages, 2029 KiB

Open AccessArticle

Mott Law exp(T₀/T)^1/4 and Scaling Properties of the Oxygen-Deficient Tenorite CuO_0.75

by Danijel Djurek, Mladen Prester, Djuro Drobac, Vilko Mandić and Damir Pajić

Condens. Matter 2025, 10(2), 33; https://doi.org/10.3390/condmat10020033 - 11 Jun 2025

The novel sub-stoichiometric copper oxide CuO_0.75 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. CuO_0.75 resembles the mixed valence oxide Cu [...] Read more.

The novel sub-stoichiometric copper oxide CuO_0.75 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. CuO_0.75 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 CuO_0.75 compound can be perceived as a showcase material for the demonstration of a new class of high-performance magnetic materials. Full article

(This article belongs to the Section Physics of Materials)

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11 pages, 232 KiB

Open AccessReview

Antimatter Research at the CERN Antiproton Decelerator: Legacy of Guido Barbiellini Amidei

by Rafael Ferragut

Condens. Matter 2025, 10(2), 32; https://doi.org/10.3390/condmat10020032 - 3 Jun 2025

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 [...] Read more.

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. Full article

(This article belongs to the Special Issue The Universe Observed With Particle Detectors: Celebrating the Scientific Legacy of Prof. Guido Barbiellini Amidei)

14 pages, 10385 KiB

Open AccessArticle

Correlation Between Structure, Microstructure, and Magnetic Properties of AlCoCrFeNi High-Entropy Alloy

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

Condens. Matter 2025, 10(2), 31; https://doi.org/10.3390/condmat10020031 - 27 May 2025

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 [...] Read more.

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. Full article

(This article belongs to the Section Magnetism)

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11 pages, 3191 KiB

Open AccessFeature PaperArticle

Magnetic Evolution of Carrier Doping and Spin Dynamics in Diluted Magnetic Semiconductors (Ba,Na)(Zn,Mn)₂As₂

by 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 and Changqing Jin

Condens. Matter 2025, 10(2), 30; https://doi.org/10.3390/condmat10020030 - 15 May 2025

Cited by 2

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 (T_C) [...] Read more.

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 (T_C) 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 T_C DMSs. Full article

(This article belongs to the Special Issue Superstripes Physics, 3rd Edition)

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15 pages, 4030 KiB

Open AccessArticle

The Defect Charge Effect on Magnetic Anisotropy Energy and Dzyaloshinskii–Moriya Interaction of the I Vacancy and 3d Transition Metal Co-Doped Monolayer CrI₃

by Guangtian Ji, Qingqing Yang, Kun Zhang, Jueming Yang, Guixian Ge and Wentao Wang

Condens. Matter 2025, 10(2), 29; https://doi.org/10.3390/condmat10020029 - 14 May 2025

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 [...] Read more.

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 (v_I-CrI₃), 3d-transition-metal-doped (TM = Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) (3d-TM_i@CrI₃), and v_I-TM co-doped (3d-TM_i@v_I-CrI₃) monolayer CrI₃ using first-principles calculations. Our results indicate that Cr-rich conditions can promote the defect formation of v_I-CrI₃, 3d-TM_i@CrI₃, and 3d-TM_i@v_I-CrI₃ systems and demonstrate that 49 types of charged systems are stable. Among these systems, the Cu_i@v_I-CrI₃ in the +1 charge state (Cu_i^•@v_I-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 p_y and p_x 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. Full article

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8 pages, 1555 KiB

Open AccessArticle

Effect of Annealing Time of GaN Buffer Layer on Curvature and Wavelength Uniformity of Epitaxial Wafer

by Huanyou Wang, Guangqi Xie and Yingying Zhan

Condens. Matter 2025, 10(2), 28; https://doi.org/10.3390/condmat10020028 - 1 May 2025

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 [...] Read more.

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. Full article

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13 pages, 751 KiB

Open AccessArticle

Effect of t_2g-Correlations and Doping in CrSBr Ferromagnetic Semiconductor

by Luis Craco and Sabrina Silva Carara

Condens. Matter 2025, 10(2), 27; https://doi.org/10.3390/condmat10020027 - 28 Apr 2025

Cited by 1

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. [...] Read more.

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

{C r}^{3 +}

oxidation state with strongly spin-polarized

t_{2 g}

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. Full article

(This article belongs to the Section Condensed Matter Theory)

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18 pages, 23429 KiB

Open AccessArticle

Synthesis of PTh/PEDOT Films into FTO Substrate by Electrodeposition, for Energy Storage Systems

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

Condens. Matter 2025, 10(2), 26; https://doi.org/10.3390/condmat10020026 - 27 Apr 2025

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 [...] Read more.

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. Full article

(This article belongs to the Section Surface and Interfaces)

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3 pages, 145 KiB

Open AccessEditorial

Novel Radiation Facilities Based on Plasma Acceleration: The Future of Free Electron Lasers

by Marcello Coreno, Massimo Ferrario, Augusto Marcelli and Francesco Stellato

Condens. Matter 2025, 10(2), 25; https://doi.org/10.3390/condmat10020025 - 27 Apr 2025

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 [...] Full article

(This article belongs to the Special Issue Experimental Ideas for Novel FEL Facilities Based on Plasma Acceleration)

3 pages, 123 KiB

Open AccessEditorial

In-Depth Experimental and Computational Studies on Rechargeable Battery Materials

by Jan Kuriplach and Rolando Saniz

Condens. Matter 2025, 10(2), 24; https://doi.org/10.3390/condmat10020024 - 25 Apr 2025

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” [...] Full article

(This article belongs to the Special Issue Rechargeable Batteries Studied Using Advanced Spectroscopic and Computational Techniques II)

8 pages, 512 KiB

Open AccessArticle

Energy Structure of Yb³⁺-Yb³⁺ Paired Center in LiNbO₃ Crystal

by Gagik Demirkhanyan, Narine Babajanyan, Ninel Kokanyan, Michel Aillerie, Marco Bazzan and Edvard Kokanyan

Condens. Matter 2025, 10(2), 23; https://doi.org/10.3390/condmat10020023 - 25 Apr 2025

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 [...] Read more.

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. Full article

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24 pages, 3710 KiB

Open AccessReview

The Laser Powder Bed Fusion of Nd₂Fe₁₄B Permanent Magnets: The State of the Art

by Ivan Pelevin, Maria Lyange, Leonid Fedorenko, Stanislav Chernyshikhin and Irina Tereshina

Condens. Matter 2025, 10(2), 22; https://doi.org/10.3390/condmat10020022 - 24 Apr 2025

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 [...] Read more.

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. Full article

(This article belongs to the Section Magnetism)

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29 pages, 10332 KiB

Open AccessReview

Basic Aspects of Ferroelectricity Induced by Noncollinear Alignment of Spins

by I. V. Solovyev

Condens. Matter 2025, 10(2), 21; https://doi.org/10.3390/condmat10020021 - 11 Apr 2025

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

) [...] Read more.

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

I F = F

and

IT A = A

, respectively. The incompatibility of these two conditions results in breaking the inversion symmetry, which manifests itself in the electric polarization

\vec{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

\vec{P}

on the directions of spins, which can include only “antisymmetric coupling” in the bond,

{\vec{P}}_{i j} \cdot [e_{i} \times e_{j}]

, and “single-ion anisotropy”,

e_{i} \cdot

\vec{Π}

e_{i}

. Microscopically,

{\vec{P}}_{i j}

can be evaluated in the framework of superexchange theory. For the single Kramers doublet, this theory yields

{\vec{P}}_{i j} \sim {\vec{r}}_{i j}^{}

, where

{\vec{r}}_{i j}^{}

is the spin-dependent part of the position operator induced by the relativistic spin-orbit coupling.

{\vec{r}}_{i j}^{}

remains invariant under spatial inversion, providing the microscopic reason why noncollinear alignment of spins can induce

\vec{P}

even in centrosymmetric crystals. The symmetry properties of

{\vec{r}}_{i j}^{}

can be rationalized from the viewpoint of symmetry of Kramers states. Particularly, the commonly used Katsura–Nagaosa–Balatsky (KNB) rule

\vec{P} \propto {\vec{ϵ}}_{j i} \times [e_{i} \times e_{j}]

(

{\vec{ϵ}}_{j i}

being the direction of the bond

i j

) can be justified only for relatively high symmetry of the bonds. The single-ion anisotropy vanishes for the spin

\frac{1}{2}

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. Full article

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