Condensed Matter

11 pages, 669 KiB

Open AccessArticle

Gauge Theories of Josephson Junction Arrays: Why Disorder Is Irrelevant for the Electric Response of Disordered Superconducting Films

by Carlo A. Trugenberger

Condens. Matter 2023, 8(3), 85; https://doi.org/10.3390/condmat8030085 - 19 Sep 2023

Cited by 2 | Viewed by 1709

Abstract

We review the topological gauge theory of Josephson junction arrays and thin film superconductors, stressing the role of the usually forgotten quantum phase slips, and we derive their quantum phase structure. A quantum phase transition from a superconducting to the dual, superinsulating phase [...] Read more.

We review the topological gauge theory of Josephson junction arrays and thin film superconductors, stressing the role of the usually forgotten quantum phase slips, and we derive their quantum phase structure. A quantum phase transition from a superconducting to the dual, superinsulating phase with infinite resistance (even at finite temperatures) is either direct or goes through an intermediate bosonic topological insulator phase, which is typically also called Bose metal. We show how, contrary to a widely held opinion, disorder is not relevant for the electric response in these quantum phases because excitations in the spectrum are either symmetry-protected or neutral due to confinement. The quantum phase transitions are driven only by the electric interaction growing ever stronger. First, this prevents Bose condensation, upon which out-of-condensate charges and vortices form a topological quantum state owing to mutual statistics interactions. Then, at even stronger couplings, an electric flux tube dual to Abrikosov vortices induces a linearly confining potential between charges, giving rise to superinsulation. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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11 pages, 1670 KiB

Open AccessArticle

Composed Effects of Electron-Hole Exchange and Near-Field Interaction in Quantum-Dot-Confined Radiative Dipoles

by Jaime David Díaz-Ramírez, Shiang-Yu Huang, Bo-Long Cheng, Ping-Yuan Lo, Shun-Jen Cheng and Hanz Yecid Ramírez-Gómez

Condens. Matter 2023, 8(3), 84; https://doi.org/10.3390/condmat8030084 - 16 Sep 2023

Cited by 2 | Viewed by 1934

Abstract

Conservation of polarization is an important requirement for reliable single-photon emitters, which, in turn, are essential building blocks for light-based quantum information processing. In this work, we study the exciton-spin dynamics in a double quantum dot under the combined effects of electron-hole exchange [...] Read more.

Conservation of polarization is an important requirement for reliable single-photon emitters, which, in turn, are essential building blocks for light-based quantum information processing. In this work, we study the exciton-spin dynamics in a double quantum dot under the combined effects of electron-hole exchange and Förster resonance energy transfer. By means of numerical solutions of the quantum master equation, we simulate the time-dependent spin polarization for two neighboring dots. According to our results, under some conditions, the depolarization caused by the electron-hole exchange may be slowed by the near field-induced interdot energy transfer, suggesting a new mechanism to extend the exciton coherence time. This opens doors to alternative schemes for improved solid-state quantum light sources. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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17 pages, 1065 KiB

Open AccessArticle

Machine Learning of Nonequilibrium Phase Transition in an Ising Model on Square Lattice

by Dagne Wordofa Tola and Mulugeta Bekele

Condens. Matter 2023, 8(3), 83; https://doi.org/10.3390/condmat8030083 - 15 Sep 2023

Cited by 4 | Viewed by 2189

Abstract

This paper presents the investigation of convolutional neural network (CNN) prediction successfully recognizing the temperature of the nonequilibrium phase transitions in two-dimensional (2D) Ising spins on a square lattice. The model uses image snapshots of ferromagnetic 2D spin configurations as an input shape [...] Read more.

This paper presents the investigation of convolutional neural network (CNN) prediction successfully recognizing the temperature of the nonequilibrium phase transitions in two-dimensional (2D) Ising spins on a square lattice. The model uses image snapshots of ferromagnetic 2D spin configurations as an input shape to provide the average output predictions. By considering supervised machine learning techniques, we perform Metropolis Monte Carlo (MC) simulations to generate the configurations. In the equilibrium Ising model, the Metropolis algorithm respects detailed balance condition (DBC), while its nonequilibrium version violates DBC. Violating the DBC of the algorithm is characterized by a parameter

- 8 < ε < 8

. We find the exact result of the transition temperature

T_{c} (ε)

in terms of

ε

. If we set

ε = 0

, the usual single spin-flip algorithm can be restored, and the equilibrium configurations generated with such a set up are used to train our model. For

ε \neq 0

, the system attains the nonequilibrium steady states (NESS), and the modified algorithm generates NESS configurations (test dataset). The trained model is successfully tested on the test dataset. Our result shows that CNN can determine

T_{c} (ε \neq 0)

for various

ε

values, consistent with the exact result. Full article

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13 pages, 914 KiB

Open AccessArticle

Elliptical Quantum Rings with Variable Heights and under Spin–Orbit Interactions

by Miguel E. Mora-Ramos, Juan A. Vinasco, A. Radu, Ricardo L. Restrepo, Alvaro L. Morales, Mehmet Sahin, Omar Mommadi, José Sierra-Ortega, Gene Elizabeth Escorcia-Salas and Carlos A. Duque

Condens. Matter 2023, 8(3), 82; https://doi.org/10.3390/condmat8030082 - 11 Sep 2023

Cited by 2 | Viewed by 1977

Abstract

We investigate the electronic properties of a semiconductor quantum ring with an elliptical shape and non-uniform height, allowing for distributed quantum-dot-like bulges along its perimeter. The adiabatic approximation and the finite element method are combined to calculate the allowed electron states in the [...] Read more.

We investigate the electronic properties of a semiconductor quantum ring with an elliptical shape and non-uniform height, allowing for distributed quantum-dot-like bulges along its perimeter. The adiabatic approximation and the finite element method are combined to calculate the allowed electron states in the structure under the effective mass approximation, considering the contributions from Rashba and Dresselahaus spin–orbit interactions and the Zeeman effect in the presence of an applied magnetic field. We discuss the features of the calculated spectra for two different ring geometries: a symmetric one with four dot-like bulges, and an asymmetric one with three hilled protuberances. The information about those states allows us to evaluate the linear optical absorption response associated with interlevel transitions between the ground and lowest excited states. This phenomenon takes place at resonant energies of only a few milielectronvolts. It is observed that spin–orbit interactions tend to quench this response under zero-field conditions in the case of symmetric confinement. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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17 pages, 3481 KiB

Open AccessArticle

A DFT + U Study on the Stability of Small Cu_N Clusters (N = 3–6 Atoms): Calculation of Phonon Frequencies

by Luis A. Alcalá-Varilla, Rafael E. Ponnefz-Durango, Nicola Seriani, Eduard Araujo-Lopez and Javier A. Montoya

Condens. Matter 2023, 8(3), 81; https://doi.org/10.3390/condmat8030081 - 11 Sep 2023

Cited by 1 | Viewed by 1799

Abstract

Despite the interest in copper clusters, a consensus on their atomic structure is still lacking. The experimental observation of isolated clusters is difficult, and theoretical predictions vary widely. The latter is because one must adequately describe the closed shell of d electrons both [...] Read more.

Despite the interest in copper clusters, a consensus on their atomic structure is still lacking. The experimental observation of isolated clusters is difficult, and theoretical predictions vary widely. The latter is because one must adequately describe the closed shell of d electrons both in its short- and long-range effects. Herein, we investigate the stability of small copper clusters (Cu

_{N}

, N = 3–6 atoms) using spin-polarized DFT calculations under the GGA approximation, the Hubbard U correction, and the van der Waals forces. We found that the spin-polarized and vdW contributions have little effect on the binding energies of the isomers. The inclusion of U represents the most relevant contribution to the ordering of the Cu

_{N}

isomers, and our calculated binding energies for the clusters agreed with the experimental values. We also found that atomic relaxations alone are not enough to determine the stability of small copper clusters. It is also necessary to build the energy landscape or calculate the vibrational frequencies of the isomers. We found that the vibrational frequencies of the isomers were in the THz range and the normal modes of vibration were discrete. This approach is relevant to future studies involving isolated or supported copper clusters. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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15 pages, 1288 KiB

Open AccessReview

Prospects of Using Fe-Ga Alloys for Magnetostrictive Applications at High Frequencies

by Vasily Milyutin, Radovan Bureš and Maria Fáberová

Condens. Matter 2023, 8(3), 80; https://doi.org/10.3390/condmat8030080 - 8 Sep 2023

Cited by 3 | Viewed by 1868

Abstract

Fe-Ga is a promising magnetostrictive rare-earth free alloy with an attractive combination of useful properties. In this review, we consider this material through the lens of its potential use in magnetostrictive applications at elevated frequencies. The properties of the Fe-Ga alloy are compared [...] Read more.

Fe-Ga is a promising magnetostrictive rare-earth free alloy with an attractive combination of useful properties. In this review, we consider this material through the lens of its potential use in magnetostrictive applications at elevated frequencies. The properties of the Fe-Ga alloy are compared with other popular magnetostrictive alloys. The two different approaches to reducing eddy current losses for such applications in the context of the Fe-Ga alloy, in particular, the fabrication of thin sheets and Fe-Ga/epoxy composites, are discussed. For the first time, the results of more than a decade of research aimed at developing each of these approaches are analyzed and summarized. The features of each approach, as well as the advantages and disadvantages, are outlined. In general, it has been shown that the Fe-Ga alloy is the most promising magnetostrictive material for use at elevated frequencies (up to 100 kHz) compared to analogs. However, for a wide practical application of the alloy, it is still necessary to solve several problems, which are described in this review. Full article

(This article belongs to the Special Issue Selected Papers from the 8th International Conference on Superconductivity and Magnetism (ICSM2023))

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14 pages, 911 KiB

Open AccessArticle

Double Quantum Ring under an Intense Nonresonant Laser Field: Zeeman and Spin-Orbit Interaction Effects

by Miguel E. Mora-Ramos, Juan A. Vinasco, Adrian Radu, Ricardo L. Restrepo, Alvaro L. Morales, Mehmet Sahin, Omar Mommadi, José Sierra-Ortega, Gene Elizabeth Escorcia-Salas, Christian Heyn, Derfrey A. Duque and Carlos A. Duque

Condens. Matter 2023, 8(3), 79; https://doi.org/10.3390/condmat8030079 - 8 Sep 2023

Viewed by 2300

Abstract

We theoretically investigate the properties of an electron energy spectrum in a double GaAs-Al_0.3Ga_0.7As quantum ring by using the effective mass and adiabatic approximations, together with a realistic description of the confining potential profile, which is assumed to be [...] Read more.

We theoretically investigate the properties of an electron energy spectrum in a double GaAs-Al_0.3Ga_0.7As quantum ring by using the effective mass and adiabatic approximations, together with a realistic description of the confining potential profile, which is assumed to be deformed due to the application of an intense nonresonant laser field. The effects of the applied magnetic field and spin-orbit interaction are included. We discuss the features of the lowest confined energy levels under a variation of magnetic field strengths and intense laser parameters. The influence of this external probe on the linear optical absorption response associated with interlevel transitions is analyzed by considering both the presence and absence of spin-orbit effects. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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9 pages, 1663 KiB

Open AccessEditor’s ChoiceArticle

The Superconducting Dome in Artificial High-T_c Superlattices Tuned at the Fano–Feshbach Resonance by Quantum Design

by Gennady Logvenov, Nicolas Bonmassar, Georg Christiani, Gaetano Campi, Antonio Valletta and Antonio Bianconi

Condens. Matter 2023, 8(3), 78; https://doi.org/10.3390/condmat8030078 - 6 Sep 2023

Cited by 4 | Viewed by 2085

Abstract

While the search for new high-temperature superconductors had been driven by the empirical “trials and errors” method for decades, we now report the synthesis of Artificial High-T_c Superlattices (AHTS) designed by quantum mechanics theory at the nanoscale. This discovery paves the [...] Read more.

While the search for new high-temperature superconductors had been driven by the empirical “trials and errors” method for decades, we now report the synthesis of Artificial High-T_c Superlattices (AHTS) designed by quantum mechanics theory at the nanoscale. This discovery paves the way for engineering a new class of high-temperature superconductors, following the predictions of the Bianconi Perali Valletta (BPV) theory recently implemented in 2022 by Mazziotti et al. including Rashba spin-orbit coupling to create nanoscale AHTS composed of quantum wells. The high-T_c superconducting properties within these superlattices are controlled by a conformational parameter of the superlattice geometry, specifically, the ratio L/d which represents the thickness of La₂CuO₄ layers (L) relative to the superlattice period (d). Using molecular beam epitaxy, we have successfully grown numerous AHTS samples. These samples consist of initial layers of stoichiometric La₂CuO₄ units with a thickness L, doped by interface space charge, and intercalated with second layers of non-superconducting metallic material, La_1.55Sr_0.45CuO₄ with thickness denoted as W = d − L. This configuration forms a quantum superlattice with periodicity d. The agreement observed between the experimental dependence T_c (the superconducting transition temperature) versus L/d ratio and the predictions of the BPV theory for AHTS in the form of the superconducting dome validates the hypothesis that the superconducting dome arises from the Fano–Feshbach or shape resonance in multigap superconductivity driven by quantum nanoscale confinement. Full article

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12 pages, 5845 KiB

Open AccessArticle

Effect of the Spatially-Varied Electron Mean Free Path on Vortex Matter in a Superconducting Pb Island Grown on Si (111)

by Jesús González, Jader González, Fernando Durán, Carlos Salas and Jorge Gómez

Condens. Matter 2023, 8(3), 77; https://doi.org/10.3390/condmat8030077 - 5 Sep 2023

Viewed by 1506

Abstract

In this work we report theoretical calculations of a superconducting island in a strong vortex confinement regime. The obtained results reveal the evolution of the superconducting condensate with an applied magnetic field, depending on the spatial profile of the electron mean-free path in [...] Read more.

In this work we report theoretical calculations of a superconducting island in a strong vortex confinement regime. The obtained results reveal the evolution of the superconducting condensate with an applied magnetic field, depending on the spatial profile of the electron mean-free path in the sample. The results of this study provide an insight about the emergent superconducting properties under such conditions, using the Ginzburg-Landau numerical simulations where spatial variation of thickness of the island and the corresponding variation of the mean free path, omnipresent in similar structures of Pb grown on Si (111), are taken into account. These results offer a new route to tailor superconducting circuits by nanoengineered mean free path, using for example the controlled ion-bombardment on thin films, benefiting from the here shown impact of the spatially-varying mean free path on the vortex distribution, phase of superconducting order parameter, and the critical fields. Full article

(This article belongs to the Section Superconductivity)

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15 pages, 5083 KiB

Open AccessArticle

Ab Initio Study of Structural, Electronic, and Thermal Properties of Pt/Pd-Based Alloys

by Louise Magdalene Botha, Cecil Naphtaly Moro Ouma, Kingsley Onyebuchi Obodo, Dmitri Georgievich Bessarabov, Denis Lvovich Sharypin, Pyotr Sergeevich Varyushin and Elizaveta Ivanovna Plastinina

Condens. Matter 2023, 8(3), 76; https://doi.org/10.3390/condmat8030076 - 5 Sep 2023

Cited by 2 | Viewed by 1814

Abstract

Alloys are beneficial in numerous applications since they combine the desirable properties of different metals. In this regard, Pt/Pd alloys have been investigated as a replacement for Pt, which is the standard catalyst used in various catalytic processes. However, there are still gaps [...] Read more.

Alloys are beneficial in numerous applications since they combine the desirable properties of different metals. In this regard, Pt/Pd alloys have been investigated as a replacement for Pt, which is the standard catalyst used in various catalytic processes. However, there are still gaps in our understanding of the structural, mechanical, and thermodynamic properties of Pt/Pd alloys. This study was conducted using density functional theory (DFT) calculations to investigate the electronic, elasticity, mechanical, and thermodynamic properties of Pt/Pd alloys and compared them to pristine Pt and Pd structures. The results indicate that the considered Pt/Pd alloy structures, PtPd₃, PtPd, Pt₃Pd, and Pt₇Pd, are energetically favourable based on their formation energies. These structures also satisfy Born’s stability criteria and are elastically stable. The phonon density of states showed that the considered Pt/Pd alloy structures are dynamically stable, with no imaginary modes present. Additionally, the Pt atom dominates at lower frequencies, while the Pd atom dominates at higher frequencies, as seen in the phonon band structure. The electronic density of states revealed that the considered Pt/Pd alloy structures have a metallic character and are non-magnetic. These findings contribute to a better understanding of the properties and stability of Pt/Pd alloy structures that are relevant in various fields, including materials science and catalysis. Full article

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13 pages, 335 KiB

Open AccessArticle

Hubbard Bands and Exotic States in Doped and Undoped Mott Systems: The Kotliar–Ruckenstein Representation

by Valentin Yu. Irkhin

Condens. Matter 2023, 8(3), 75; https://doi.org/10.3390/condmat8030075 - 28 Aug 2023

Viewed by 1486

Abstract

The slave–particle representation is a promising method to treat the properties of exotic strongly correlated systems. We develop a unified approach to describe both the paramagnetic state with possible spin–liquid features and states with strong long-range or short-range magnetic order. Combining the Kotliar–Ruckenstein [...] Read more.

The slave–particle representation is a promising method to treat the properties of exotic strongly correlated systems. We develop a unified approach to describe both the paramagnetic state with possible spin–liquid features and states with strong long-range or short-range magnetic order. Combining the Kotliar–Ruckenstein representation and fractionalized spin–liquid deconfinement picture, the Mott transition and Hubbard subbands are considered. The spectrum in the insulating state is significantly affected by the presence of the spinon spin–liquid spectrum and a hidden Fermi surface. Presenting a modification of the Kotliar–Ruckenstein representation in the spin–wave region, we treat the case of magnetic order, with special attention being paid to the half-metallic ferromagnetic state. The formation of small and large Fermi surfaces for doped current carriers in the antiferromagnetic state is also discussed. Full article

(This article belongs to the Special Issue Selected Papers from the 8th International Conference on Superconductivity and Magnetism (ICSM2023))

13 pages, 1388 KiB

Open AccessArticle

Properties of Blue Phosphorene Nanoribbon-P3HT Polymer Heterostructures: DFT First Principles Calculations

by Benita Turiján-Clara, Julián D. Correa, Miguel E. Mora-Ramos and Carlos A. Duque

Condens. Matter 2023, 8(3), 74; https://doi.org/10.3390/condmat8030074 - 22 Aug 2023

Cited by 1 | Viewed by 1836

Abstract

Recently, 2D phosphorus allotropes have arisen as possible candidates for technological applications among the family of the so-called Xene layered materials. In particular, the energy band structure of blue phosphorene (BP) exhibits a medium-size semiconductor gap that tends to widen in the case [...] Read more.

Recently, 2D phosphorus allotropes have arisen as possible candidates for technological applications among the family of the so-called Xene layered materials. In particular, the energy band structure of blue phosphorene (BP) exhibits a medium-size semiconductor gap that tends to widen in the case of using this material in the form of ribbons. BP nanoribbons have attracted recent interest for their implication in the improvement in efficiency of novel solar cells. On the other hand, compound poly (3-hexylthiophene) (P3HT) is used as the semiconducting core of organic field effect transistors owing to such useful features as high carrier mobility. Here, we theoretically investigate the electronic properties of a heterostructure combination of BP—in the form of nanoribbons—with a P3HT polymer chain on top in order to identify the features of band alignment. The work is performed using first principles calculations via DFT, employing different exchange correlation approaches for comparison: PBE, HSE06 and DFT-1/2. It is found that, under DFT-1/2, such a heterostructure has a type-II band alignment. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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13 pages, 2943 KiB

Open AccessArticle

PbF₂–CdF₂–SrF₂ Ternary Solid Solution: Crystal Growth and Investigation

by Irina I. Buchinskaya, Ivan O. Goryachuk, Nikolay I. Sorokin, Victor I. Sokolov and Denis N. Karimov

Condens. Matter 2023, 8(3), 73; https://doi.org/10.3390/condmat8030073 - 16 Aug 2023

Cited by 2 | Viewed by 1457

Abstract

Crystals based on alkaline earth metal difluorides are widely used optical materials. In this study, in order to expand the range of optical matrices, multicomponent Pb_1−x−yCd_xSr_yF₂ (0.27 < x < 0.55, 0.06 < [...] Read more.

Crystals based on alkaline earth metal difluorides are widely used optical materials. In this study, in order to expand the range of optical matrices, multicomponent Pb_1−x−yCd_xSr_yF₂ (0.27 < x < 0.55, 0.06 < y < 0.18) solid solution crystals with a fluorite structure (sp. gr. Fm-3m) were grown from melt using the vertical directional crystallization technique for the first time. The densities and refractive indices of the grown crystals vary depending on the quantitative content components (x and y) in the ranges of 6.6039(5)–7.5232(5) g/cm³ and 1.6403–1.7084, respectively. The optical transmission and electrochemical impedance spectra were studied. The homogenous composition regions of non-cellular crystallization of this ternary solid solution at a crystallization rate of 6 mm/h and an interface temperature gradient of 80 deg/cm were experimentally determined as 0.30 < x < 0.35, 0 < y < 0.6. These grown crystalline materials may be of interest as high-density highly refractive cubic isomorphic hosts and low-temperature ionic conductors (~2 × 10⁻⁵ S/cm at room temperature) for various applications. Full article

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13 pages, 2742 KiB

Open AccessArticle

Superlattices, Bonding-Antibonding, Fermi Surface Nesting, and Superconductivity

by Jose A. Alarco and Ian D. R. Mackinnon

Condens. Matter 2023, 8(3), 72; https://doi.org/10.3390/condmat8030072 - 15 Aug 2023

Cited by 2 | Viewed by 2092

Abstract

Raman and synchrotron THz absorption spectral measurements on MgB₂ provide experimental evidence for electron orbital superlattices. In earlier work, we have detected THz spectra that show superlattice absorption peaks with low wavenumbers, for which spectral density evolves and intensifies after cooling below [...] Read more.

Raman and synchrotron THz absorption spectral measurements on MgB₂ provide experimental evidence for electron orbital superlattices. In earlier work, we have detected THz spectra that show superlattice absorption peaks with low wavenumbers, for which spectral density evolves and intensifies after cooling below the superconducting transition temperature for MgB₂. In this work, we show how these observations indicate a direct connection to superconducting properties and mechanisms. Bonding–antibonding orbital character is identified in calculated electronic band structures and Fermi surfaces consistent with superlattice structures along the c-axis. DFT calculations show that superlattice folding of reciprocal space generates Brillouin zone boundary reflections, Umklapp processes, and substantially enhances nesting relationships. Tight binding equations are compared with expected charge density waves from nesting relationships and adjusted to explicitly accommodate these linked processes. Systematic analysis of electronic band structures and Fermi surfaces allows for direct identification of Cooper pairing and the superconducting gap, particularly when the k-grid resolution of a calculation is suitably calibrated to structural parameters. Thus, we detail a robust and accurate DFT re-interpretation of BCS superconductivity for MgB₂. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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14 pages, 896 KiB

Open AccessArticle

Electric and Magnetic Fields Effects in Vertically Coupled GaAs/Al_xGa_1−xAs Conical Quantum Dots

by Ana María López Aristizábal, Fernanda Mora Rey, Álvaro Luis Morales, Juan A. Vinasco and Carlos Alberto Duque

Condens. Matter 2023, 8(3), 71; https://doi.org/10.3390/condmat8030071 - 15 Aug 2023

Cited by 2 | Viewed by 1610

Abstract

Vertically coupled quantum dots have emerged as promising structures for various applications such as single photon sources, entangled quantum pairs, quantum computation, and quantum cryptography. We start with a structure composed of two vertically coupled GaAs conical quantum dots surrounded by Al

_{x}

[...] Read more.

Vertically coupled quantum dots have emerged as promising structures for various applications such as single photon sources, entangled quantum pairs, quantum computation, and quantum cryptography. We start with a structure composed of two vertically coupled GaAs conical quantum dots surrounded by Al

_{x}

Ga

_{1 - x}

, and the effects of the applied electric and magnetic fields on the energies are evaluated using the finite element method. In addition, the effects are evaluated by including the presence of a shallow-donor impurity. The electron binding energy behavior is analyzed, and the effects on the photoionization cross-section are studied. Calculations are carried out in the effective mass and parabolic conduction band approximations. Our results show a notable dependence on the electric and magnetic fields applied to the photoionization cross-section. In general, it has been observed that both the electric and magnetic fields are useful parameters for inducing blueshifts of the resonant photoionization cross-section structure, which is accompanied by a drop in its magnitude. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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18 pages, 31481 KiB

Open AccessArticle

The Transport and Optical Characteristics of a Metal Exposed to High-Density Energy Fluxes in Compressed and Expanded States of Matter

by Nikolay B. Volkov and Alexander I. Lipchak

Condens. Matter 2023, 8(3), 70; https://doi.org/10.3390/condmat8030070 - 11 Aug 2023

Cited by 1 | Viewed by 1590

Abstract

This article presents a theoretical study of the optical and transport properties of metals. Iron, as an example, was used to discuss, through a theoretical description, the peculiarities of these properties in the compressed and expanded states under the influence of high-density energy [...] Read more.

This article presents a theoretical study of the optical and transport properties of metals. Iron, as an example, was used to discuss, through a theoretical description, the peculiarities of these properties in the compressed and expanded states under the influence of high-density energy fluxes. By solving the semi-classical Boltzmann equation for conduction electrons for a broad range of densities and temperatures, the expressions of electrical conductivity, electronic thermal conductivity, and thermoelectric coefficient calculations were derived. The real and imaginary parts of the iron permittivity and the energy absorption coefficient for the first and second harmonics of Nd:YAG laser radiation were obtained. The calculation peculiarities of the metal’s optical characteristics of matter in an expanded state in a broad range of densities and temperatures were considered. The analysis of the obtained results shows their agreement with the theoretical description for cases of ideal non-degenerate and dense degenerate electron plasmas. It is shown that the behavior of the electrical conductivity and optical characteristics in the critical and supercritical regions of density and temperature are in agreement with the known experimental results. Full article

(This article belongs to the Topic Applications of Photonics, Laser, Plasma and Radiation Physics)

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9 pages, 3846 KiB

Open AccessFeature PaperArticle

Multiband Superconductivity in High-Pressure Sulfur Hydrides

by Giovanni Alberto Ummarino and Antonio Bianconi

Condens. Matter 2023, 8(3), 69; https://doi.org/10.3390/condmat8030069 - 9 Aug 2023

Cited by 2 | Viewed by 1336

Abstract

The temperature dependence of the two superconducting gaps in pressurised

H_{3} S

at 155 GPa with a critical temperature of 203 K has been determined using a data analysis of the experimental curve of the upper critical magnetic field as a function [...] Read more.

The temperature dependence of the two superconducting gaps in pressurised

H_{3} S

at 155 GPa with a critical temperature of 203 K has been determined using a data analysis of the experimental curve of the upper critical magnetic field as a function of temperature in the framework of the two-band s-wave Eliashberg theory. Two different phonon-mediated intra-band Cooper pairing channels in a regime of moderate strong couplings have the key role of the pair-exchange interaction between the two gaps, giving the two non-diagonal terms of the coupling tensor, which are missing in the single-band s-wave Eliashberg theory. The results provide a prediction of the different temperature dependence of the small and large gaps as a function of temperature, which provides evidence of multigap superconductivity in

H_{3} S

. Full article

(This article belongs to the Special Issue Superstripes Physics, 2nd Edition)

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12 pages, 4161 KiB

Open AccessArticle

ETPTA Inverse Photonic Crystals for the Detection of Alcohols

by Matin Ashurov, Stella Kutrovskaya, Alexander Baranchikov, Sergey Klimonsky and Alexey Kavokin

Condens. Matter 2023, 8(3), 68; https://doi.org/10.3390/condmat8030068 - 8 Aug 2023

Cited by 1 | Viewed by 2158

Abstract

We developed a comparatively simple and inexpensive approach for the determination of the concentration of alcohols in water. The method is based on the study of the optical properties of ethoxylate trimethylolpropane triacrylate (ETPTA) inverse photonic crystals (IPhCs). The position of the transmission [...] Read more.

We developed a comparatively simple and inexpensive approach for the determination of the concentration of alcohols in water. The method is based on the study of the optical properties of ethoxylate trimethylolpropane triacrylate (ETPTA) inverse photonic crystals (IPhCs). The position of the transmission minimum associated with the first photonic stop band (PSB) is used as the analytical signal. The PSB position depends on the swelling degree of ETPTA photoresist and the refractive index of the tested alcohols and their mixtures with water. The signal increases linearly with increasing concentration of ethylene glycol and increases nonlinearly but monotonically with the concentration of methanol and ethanol in water. Sensitivity to alcohols, in the case of the ethylene glycol–water mixtures, reached about 0.55 nm/v.% or 560 nm/RIU (refractive index unit), which is sufficient for various applications in bio/chemical detection and environmental monitoring. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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17 pages, 2549 KiB

Open AccessFeature PaperArticle

Interactions and Dynamics of One-Dimensional Droplets, Bubbles and Kinks

by Garyfallia C. Katsimiga, Simeon I. Mistakidis, Boris A. Malomed, Dimitris J. Frantzeskakis, Ricardo Carretero-Gonzalez and Panayotis G. Kevrekidis

Condens. Matter 2023, 8(3), 67; https://doi.org/10.3390/condmat8030067 - 4 Aug 2023

Cited by 13 | Viewed by 1933

Abstract

We explore the dynamics and interactions of multiple bright droplets and bubbles, as well as the interactions of kinks with droplets and with antikinks, in the extended one-dimensional Gross–Pitaevskii model including the Lee–Huang–Yang correction. Existence regions are identified for the one-dimensional droplets and [...] Read more.

We explore the dynamics and interactions of multiple bright droplets and bubbles, as well as the interactions of kinks with droplets and with antikinks, in the extended one-dimensional Gross–Pitaevskii model including the Lee–Huang–Yang correction. Existence regions are identified for the one-dimensional droplets and bubbles in terms of their chemical potential, verifying the stability of the droplets and exposing the instability of the bubbles. The limiting case of the droplet family is a stable kink. The interactions between droplets demonstrate in-phase (out-of-phase) attraction (repulsion), with the so-called Manton’s method explicating the observed dynamical response, and mixed behavior for intermediate values of the phase shift. Droplets bearing different chemical potentials experience mass-exchange phenomena. Individual bubbles exhibit core expansion and mutual attraction prior to their destabilization. Droplets interacting with kinks are absorbed by them, a process accompanied by the emission of dispersive shock waves and gray solitons. Kink–antikink interactions are repulsive, generating counter-propagating shock waves. Our findings reveal dynamical features of droplets and kinks that can be detected in current experiments. Full article

(This article belongs to the Topic Quantum Droplets)

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19 pages, 1308 KiB

Open AccessArticle

Effect of External Fields on the Electronic and Optical Properties in ZnTe/CdSe and CdSe/ZnTe Spherical Quantum Dots

by Rafael G. Toscano-Negrette, José C. León-González, Juan A. Vinasco, Alvaro L. Morales, Miguel E. Mora-Ramos and Carlos A. Duque

Condens. Matter 2023, 8(3), 66; https://doi.org/10.3390/condmat8030066 - 2 Aug 2023

Cited by 4 | Viewed by 1713

Abstract

A theoretical analysis was conducted to examine the electronic and optical properties of a confined electron and a hole in a type-II core-shell spherical quantum dot composed of CdSe/ZnTe and ZnTe/CdSe. The Schrödinger equation for the electron and the hole was numerically solved [...] Read more.

A theoretical analysis was conducted to examine the electronic and optical properties of a confined electron and a hole in a type-II core-shell spherical quantum dot composed of CdSe/ZnTe and ZnTe/CdSe. The Schrödinger equation for the electron and the hole was numerically solved using COMSOL-Multiphysics software in the 2D axisymmetric module, which employs the finite element method under the effective mass approximation. A Fortran code was utilized to calculate excitonic energy, specifically designed to solve the Coulomb integral. The calculations encompassed variations in the inner radius (

R_{1}

), as well as variations in the electric (

F_{z}

) and magnetic (B) fields along the z-axis. The absorption coefficients were determined for transitions between the hole and electron ground states, considering z-polarized incident radiation. Including a magnetic field increases the transition energy, consequently causing the absorption peaks to shift toward the blue region of the spectrum. On the other hand, the electric field decreased the overlap of the electron and hole wavefunctions. As a result, the amplitude of the absorption peaks decreased with an increase in the electric field. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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7 pages, 1257 KiB

Open AccessArticle

Influence of Frustration Effects on the Critical Current of DC SQUID

by Iman N. Askerzade

Condens. Matter 2023, 8(3), 65; https://doi.org/10.3390/condmat8030065 - 28 Jul 2023

Viewed by 1545

Abstract

In this paper, we conducted the calculation of the critical current of DC SQUID based on the Josephson junction on a multi-band superconductor with frustration effect. It is shown that the critical current of DC SQUID on the frustrated multi-band superconductor with a [...] Read more.

In this paper, we conducted the calculation of the critical current of DC SQUID based on the Josephson junction on a multi-band superconductor with frustration effect. It is shown that the critical current of DC SQUID on the frustrated multi-band superconductor with a small geometrical inductance of the loop is determined by the supercurrent amplitude in different channels and by the external magnetic field. In the case of a DC SQUID with high inductance, frustration effects can be ignored. Full article

(This article belongs to the Special Issue Selected Papers from the 8th International Conference on Superconductivity and Magnetism (ICSM2023))

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16 pages, 2875 KiB

Open AccessArticle

Nanoscale Structural Phase Transitions in Aqueous Solutions of Organic Molecules

by Nikolai Bunkin, Leonard Sabirov, Denis Semenov, Faxriddin Ismailov and Muxriddin Khasanov

Condens. Matter 2023, 8(3), 64; https://doi.org/10.3390/condmat8030064 - 26 Jul 2023

Viewed by 1293

Abstract

Adiabatic compressibility β_S of the 4-methylpyridine + water solution is investigated in a wide concentration and temperature variation interval using Mandelstam–Brillouin scattering spectroscopy. The adiabatic compressibility minimum caused by the microinhomogeneous structure of the solution is experimentally established at the concentration of [...] Read more.

Adiabatic compressibility β_S of the 4-methylpyridine + water solution is investigated in a wide concentration and temperature variation interval using Mandelstam–Brillouin scattering spectroscopy. The adiabatic compressibility minimum caused by the microinhomogeneous structure of the solution is experimentally established at the concentration of 0.06 molar fractions of 4-methylpyridine in the solution. The results of the investigations allow the construction of a diagram of possible states caused by a continuous three-dimensional hydrogen bond network of water. The results of experimental study of the excessive hypersound absorption in acetone + water and 3-methylpyridine + water solutions are discussed based on the conclusions of the theory of high-frequency sound scattering near the critical point (developed by Chaban) and the Landau theory. These results are described within the framework of the Landau and Chaban theories and explained by the existence of two different states with minimum thermodynamic stability in the solution. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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11 pages, 621 KiB

Open AccessArticle

Exploring Photonic Crystals: Band Structure and Topological Interface States

by Melquiades de Dios-Leyva, Andy Márquez-González and Carlos Alberto Duque

Condens. Matter 2023, 8(3), 63; https://doi.org/10.3390/condmat8030063 - 25 Jul 2023

Cited by 1 | Viewed by 1541

Abstract

The physical mechanisms supporting the existence of topological interface modes in photonic structures, formed with the concatenation of two finite, N-period, one-dimensional photonic crystals, are investigated. It is shown that these mechanisms originate from a specific configuration of bands and bandgaps of [...] Read more.

The physical mechanisms supporting the existence of topological interface modes in photonic structures, formed with the concatenation of two finite, N-period, one-dimensional photonic crystals, are investigated. It is shown that these mechanisms originate from a specific configuration of bands and bandgaps of topological origin in the band structure of the concatenated structure. Our analysis reveals that the characteristics of such a configuration depend on the structural parameters, including the number, N, of unit cells, and determine the properties of the corresponding resonant transmission peak. It was shown that the width and maximum value of the transmission peaks decrease with N. These results not only provide new physical insight into the origin and nature of such modes, but also can be used to control and manipulate the transmission peak properties, such as peak values, full width at half maximum (FWHM), and Q-factor, which are of special interest in the fields of optical sensing, filters, etc. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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9 pages, 7856 KiB

Open AccessArticle

The Synthesis of C₇₀ Fullerene Nanowhiskers Using the Evaporating Drop Method

by Sagdulla A. Bakhramov, Urol K. Makhmanov and Bobirjon A. Aslonov

Condens. Matter 2023, 8(3), 62; https://doi.org/10.3390/condmat8030062 - 24 Jul 2023

Cited by 3 | Viewed by 1868

Abstract

Semiconductor nanowhiskers, particularly nanostructured whiskers based on zero-dimensional (0D) C₇₀ fullerene, are being actively discussed due to the great potential of their application in modern electronics. For the first time, we proposed and implemented a method for the synthesis of nanostructured C [...] Read more.

Semiconductor nanowhiskers, particularly nanostructured whiskers based on zero-dimensional (0D) C₇₀ fullerene, are being actively discussed due to the great potential of their application in modern electronics. For the first time, we proposed and implemented a method for the synthesis of nanostructured C₇₀ fullerene whiskers based on the self-organization of C₇₀ molecules during the thermal evaporation of C₇₀ droplets on the substrate surface. We found that the onset of the synthesis of C₇₀ nanowhiskers upon the evaporation of drops of a C₇₀ solution in toluene on the substrate surface depends on the substrate temperature. We have provided experimental evidence that an increase in both the C₇₀ concentration in the initial drop and the substrate temperature leads to an increase in the geometric dimensions of C₇₀ nanowhiskers. The obtained results provide useful vision on the role of solute concentration and substrate temperature in the synthesis of one-dimensional materials. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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13 pages, 1599 KiB

Open AccessArticle

Structural, Electronic, and Optical Properties of Wurtzite V_xAl_1−xN Alloys: A First-Principles Study

by Gene Elizabeth Escorcia-Salas, Diego Restrepo-Leal, Oscar Martinez-Castro, William López-Pérez and José Sierra-Ortega

Condens. Matter 2023, 8(3), 61; https://doi.org/10.3390/condmat8030061 - 19 Jul 2023

Cited by 1 | Viewed by 1703

Abstract

We present a comprehensive study on the structural, electronic, and optical properties of

V_{x} A l_{1 - x} N

ternary alloys using first-principles calculations. Our investigations employ the full-potential linearized augmented-plane-wave (FP-LAPW) method within the density functional theory (DFT) framework. The [...] Read more.

We present a comprehensive study on the structural, electronic, and optical properties of

V_{x} A l_{1 - x} N

ternary alloys using first-principles calculations. Our investigations employ the full-potential linearized augmented-plane-wave (FP-LAPW) method within the density functional theory (DFT) framework. The impact of varying vanadium composition (x = 0, 0.25, 0.5, 0.75, 1) on the structural, electronic, and optical characteristics of wurtzite

V_{x} A l_{1 - x} N

alloys is examined in detail. Our findings reveal a distinct nonlinear relationship between the lattice constant, bulk modulus, and the concentration of vanadium (x) in the

V_{x} A l_{1 - x} N

alloys. An analysis of the electronic band structures and densities of states reveals a metallic behavior in the

V_{x} A l_{1 - x} N

alloys, primarily driven by the V-d states near the Fermi energy. These results shed light on the electronic properties of the alloys, contributing to a deeper understanding of their potential for various applications. Furthermore, we calculate various optical properties, including the real and imaginary dielectric functions, refractive index, energy loss spectrum, and reflectivity. The obtained optical functions provide valuable insights into the optical behavior of the

V_{x} A l_{1 - x} N

alloys. The results contribute to the fundamental knowledge of these materials and their potential applications in various fields. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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19 pages, 11062 KiB

Open AccessArticle

Theoretical Study of Electronic and Thermal Transport Properties through a Single-Molecule Junction of Catechol

by Erika Y. Soto-Gómez, Judith Helena Ojeda Silva, John A. Gil-Corrales, Daniel Gallego, Mikel F. Hurtado Morales, Alvaro L. Morales and Carlos A. Duque

Condens. Matter 2023, 8(3), 60; https://doi.org/10.3390/condmat8030060 - 15 Jul 2023

Cited by 3 | Viewed by 1578

Abstract

The study of molecular nanoelectronic devices has recently gained significant interest, especially their potential use as functional junctions of molecular wires. Aromatic systems with

π

-conjugated bonds within their chemical backbones, such as catechol, have attracted particular attention in this area. In this [...] Read more.

The study of molecular nanoelectronic devices has recently gained significant interest, especially their potential use as functional junctions of molecular wires. Aromatic systems with

π

-conjugated bonds within their chemical backbones, such as catechol, have attracted particular attention in this area. In this work, we focused on calculating and determining catechol’s electrical and thermal transport properties using the theoretical method of Green’s functions renormalized in a real space domain within a framework of tight-binding approximation to the first neighbors. Thus, we studied two theoretical models of catechol as a function of its geometry, obtaining striking variations in the profiles of electrical and thermal conductance, the Seebeck coefficient, and the figure of merit. The analyses of the results suggest the potential application of catechol as a likely conductive and thermoelectric molecule serving as a novel material to use in molecular electronic devices. Full article

(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)

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8 pages, 2349 KiB

Open AccessArticle

On the Optical Properties of Cr₂Ge₂Te₆ and Its Heterostructure

by Hiroshi Idzuchi, Andres E. Llacsahuanga Allcca, Amanda Victo Haglund, Xing-Chen Pan, Takuya Matsuda, Katsumi Tanigaki, David Mandrus and Yong P. Chen

Condens. Matter 2023, 8(3), 59; https://doi.org/10.3390/condmat8030059 - 14 Jul 2023

Cited by 1 | Viewed by 1938

Abstract

Recently, there has been a growing interest in two-dimensional van der Waals (vdW) magnets owing to their unique two-dimensional magnetic phenomena and potential applications. Most vdW ferromagnets have the Curie temperature below room temperature, highlighting the need to explore how to enhance their [...] Read more.

Recently, there has been a growing interest in two-dimensional van der Waals (vdW) magnets owing to their unique two-dimensional magnetic phenomena and potential applications. Most vdW ferromagnets have the Curie temperature below room temperature, highlighting the need to explore how to enhance their magnetism. In our previous report, we successfully increased the Curie temperature of the prototypical vdW magnet Cr₂Ge₂Te₆ using a NiO overlayer. In layered materials, the presence of wrinkles is often observed and evaluating them using optical microscopy proves to be useful; however, there have been limited investigations into the optical constants of vdW magnets, hampering progress in understanding their optical properties. In this study, we present the optical constants of Cr₂Ge₂Te₆ obtained through ellipsometry measurements. To account for the presence of wrinkles, we model a vacuum region between the substrate and the vdW magnet, and we calculate the reflectivity as a function of wavelength and vacuum thickness to visualize the optical image. Furthermore, we discuss the relationship between the optical constants and the electronic structure of the material. Full article

(This article belongs to the Special Issue Selected Papers from the International Conference on Quantum Materials and Technologies (ICQMT2022))

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14 pages, 2572 KiB

Open AccessArticle

The Effect of Acyl Chain Position on the 2D Monolayer Formation of Monoacyl-sn-Glycerol at the Air/Water Interface: Quantum Chemical Modeling

by Elena S. Kartashynska

Condens. Matter 2023, 8(3), 58; https://doi.org/10.3390/condmat8030058 - 13 Jul 2023

Cited by 1 | Viewed by 1186

Abstract

This paper deals with the results of quantum chemical modeling of the monoacyl-sn-glycerol 2D cluster formation at the air/water interface using a semi-empirical PM3 method. The impact of the 2 or 3 positions of the acyl substituent on the thermodynamics of [...] Read more.

This paper deals with the results of quantum chemical modeling of the monoacyl-sn-glycerol 2D cluster formation at the air/water interface using a semi-empirical PM3 method. The impact of the 2 or 3 positions of the acyl substituent on the thermodynamics of the monolayer formation is assessed for surfactants with an acyl substituent C_nH_2n+1COO chain length of n = 6–17 carbon atoms. The calculation shows a significant change in the spontaneous clusterization threshold for isomeric compounds, which differs only in the position of the acyl substituent with respect to the glycerol backbone. This change is almost equal to substituent shortening by approximately two methylene fragments. At the same time, the geometric parameters of the unit cell for resulting monolayers are not affected so drastically. The 2D films in question possess an oblique or orthorhombic unit cell with parameters for 2 and 3-monoacyl-sn-glycerol monolayers, as follows: a = 4.91 Å and 4.82 Å and b = 5.00 Å and 4.92 Å, with hydrocarbon chains tilted at t = 23.0° and 23.5°. The calculated results are in accordance with existing experimental data obtained using grazing incidence X-ray diffraction measurements and the π-A isotherm technique. Full article

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12 pages, 2997 KiB

Open AccessArticle

Tensile Microstrain Fluctuations in the BaPbO Units in Superconducting BaPb_1−xBi_xO₃ by Scanning Dispersive Micro-XANES

by Ruben Albertini, Salvatore Macis, Andrei A. Ivanov, Alexey P. Menushenkov, Alessandro Puri, Virginia Monteseguro, Boby Joseph, Wei Xu, Augusto Marcelli, Paula Giraldo-Gallo, Ian Randal Fisher, Antonio Bianconi and Gaetano Campi

Condens. Matter 2023, 8(3), 57; https://doi.org/10.3390/condmat8030057 - 11 Jul 2023

Viewed by 1884

Abstract

BaPb_1−xBi_xO₃ (BPBO) bismuthate, showing high T_C superconductivity for 0.05 < x < 0.35, is an archetypal system for studying the complex inhomogeneity of perovskite lattice favoring the emergence of quantum coherence, called the superstripes phase. Local lattice [...] Read more.

BaPb_1−xBi_xO₃ (BPBO) bismuthate, showing high T_C superconductivity for 0.05 < x < 0.35, is an archetypal system for studying the complex inhomogeneity of perovskite lattice favoring the emergence of quantum coherence, called the superstripes phase. Local lattice fluctuations, detected by EXAFS; nanoscale stripes, detected by electron microscopy; and two competing crystalline structures, detected by diffraction, are known to characterize the superconducting phase. At nanoscale [BaBiO₃] centered nanoscale units (BBO) coexist with BaPbO₃ centered (BPO) units in the BPBO perovskite; therefore, we expect a tensile microstrain in BPO units due the misfit strain between the two different lattices. Here, we report the measurement of the spatial micro-fluctuations of the local tensile microstrain ε in the BaPO units in superconducting Ba(Pb_1−xBi_x)O₃ crystals with x₁ = 0.19 an x₂ = 0.28. We show here the feasibility of applying the scanning dispersive micro-X-ray absorption near edge structure (SdμXANES) technique, using focused synchrotron radiation, to probe the microscale spatial fluctuations of the microstrain in BPO units. This unconventional real-space SdμXANES microscopy at the Pb L₃ edge has been collected in the dispersive mode. Our experimental method allows us to measure either the local Bi chemical concentration x and the local lattice microstrain of local BBO and BPO units. The 5 × 5 micron-size spots from the focused X-ray beam allowed us to obtain maps of 1600 points covering an area of 200 × 200 microns. The mapping shows a substantial difference between the spatial fluctuations of the microstrain ε and the chemical inhomogeneity x. Moreover, we show the different relations ε(x) in samples with lower (x₁ = 0.19) and higher (x₂ = 0.28) doping respect to the optimum doping (x = 0.25). Full article

(This article belongs to the Section Superconductivity)

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10 pages, 1900 KiB

Open AccessArticle

T_c Saturation and Possible Electronic Phase Separation in Strongly Overdoped Cuprates

by Amirreza Hemmatzade, Elena Medina, Ludovic Delbes, Benoît Baptiste, David Hrabovsky, Yannick Klein, Steven D. Conradson, Maarit Karppinen and Andrea Gauzzi

Condens. Matter 2023, 8(3), 56; https://doi.org/10.3390/condmat8030056 - 5 Jul 2023

Viewed by 1375

Abstract

In order to elucidate the unusual superconducting properties of cuprates in the strongly overdoped region, i.e., at hole-doping levels

p ≳ 0.4

/Cu in the CuO

_{2}

plane, we study the structural and superconducting properties of a series of Cu

_{0.75}

Mo

_{0.25}

[...] Read more.

In order to elucidate the unusual superconducting properties of cuprates in the strongly overdoped region, i.e., at hole-doping levels

p ≳ 0.4

/Cu in the CuO

_{2}

plane, we study the structural and superconducting properties of a series of Cu

_{0.75}

Mo

_{0.25}

Sr

_{2}

YCu

_{2}

O

_{7 + x}

powder samples oxygenated under high pressure using different concentrations of KClO

_{3}

up to 35 mol %. The analysis of X-ray diffraction data indicates a high purity ∼90% of all samples and suggests that the concentration, x, of extra oxygen atoms increases with increasing KClO

_{3}

concentration. Surprisingly, the

T_{c}

values remain nearly constant within the 80–85 K range independent of KClO

_{3}

concentration, which suggests a scenario of

T_{c}

saturation. In order to account for this unexpected behaviour, we put forward the hypothesis that overdoping enhances the density of unpaired holes, which is supported by the observation of large values of the Sommerfeld coefficient in all samples. We therefore propose a scenario of electronic phase separation between normal and superconducting holes. Full article

(This article belongs to the Special Issue Superstripes Physics)

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