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Condens. Matter, Volume 8, Issue 2 (June 2023) – 24 articles

Cover Story (view full-size image): A wide dissemination of optoelectronic devices over recent decades, utilizing various applications of modern photonics (from light concentration in nanophotonic waveguides to quantum information processing, etc.) has elevated the importance of investigations into properties of different types of photonic systems. In particular, a considerable effort has been put into the study of electromagnetic wave propagation in thin films and layered crystalline media. Interest in these objects is explained on the one hand by the demand of solid-state electronics for various layered structures with predetermined properties, and on the other hand by technological advances allowing for epitaxial growth of such films as well as other periodic structures with controllable characteristics. View this paper
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12 pages, 7719 KiB  
Article
Dispersion in Single-Wall Carbon Nanotube Film: An Application of Bogoliubov–Valatin Transformation for Hamiltonian Diagonalization
by Chandra M. Adhikari, Da’Shawn M. Morris, Thomas W. Noonan, Tikaram Neupane, Basu R. Lamichhane and Bhoj R. Gautam
Condens. Matter 2023, 8(2), 53; https://doi.org/10.3390/condmat8020053 - 16 Jun 2023
Viewed by 1488
Abstract
We present a theoretical study on the energy dispersion of an ultrathin film of periodically-aligned single-walled carbon nanotubes (SWCNTs) with the help of the Bogoliubov–Valatin transformation. The Hamiltonian of the film was derived using the many-particle green function technique in the Matsubara frequency [...] Read more.
We present a theoretical study on the energy dispersion of an ultrathin film of periodically-aligned single-walled carbon nanotubes (SWCNTs) with the help of the Bogoliubov–Valatin transformation. The Hamiltonian of the film was derived using the many-particle green function technique in the Matsubara frequency formalism. The periodic array of SWCNTs was embedded in a dielectric with comparatively higher permittivity than the substrate and the superstrate such that the SWCNT film became independent with the axis of quantization but keeps the thickness as the variable parameter, making the film neither two-dimensional nor three-dimensional, but transdimensional. It was revealed that the energy dispersion of the SWCNT film is thickness dependent. Full article
(This article belongs to the Section Condensed Matter Theory)
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17 pages, 1492 KiB  
Article
Influence of a Non-Resonant Intense Laser and Structural Defect on the Electronic and Optical Properties of a GaAs Quantum Ring under Inversely Quadratic Potential
by José C. León-González, Rafael G. Toscano-Negrette, Juan A. Vinasco, Alvaro L. Morales, Miguel E. Mora-Ramos and Carlos A. Duque
Condens. Matter 2023, 8(2), 52; https://doi.org/10.3390/condmat8020052 - 15 Jun 2023
Cited by 4 | Viewed by 1109
Abstract
We investigated the impact of a non-resonant intense laser, structural defects, and magnetic fields on the electronic and optical properties of a simple GaAs quantum ring under the inverse quadratic Hellmann potential, using the effective mass and parabolic band approximations. We obtained the [...] Read more.
We investigated the impact of a non-resonant intense laser, structural defects, and magnetic fields on the electronic and optical properties of a simple GaAs quantum ring under the inverse quadratic Hellmann potential, using the effective mass and parabolic band approximations. We obtained the energies and wavefunctions by solving the 2D Schrodinger’s equation using the finite-element numerical technique to analyze this. We considered circular polarization to calculate the dipole matrix elements, which were influenced by the laser field and structural defects in the system. This enabled us to study the linear absorption coefficients. Our results demonstrated that the presence of a laser field and a structural defect disrupt the axial symmetry of the problem. When only the non-resonant laser was present, a pattern of excited states appeared in pairs, which oscillated with the magnetic field. However, the amplitude of the oscillation decreased as the magnetic field strength increased, and these oscillations disappeared when the structural defect was introduced. It was also noted that the intensity and position of the linear optical absorption peaks exhibited a non-monotonic behavior with the magnetic field in the absence of a structural defect. However, this behavior changed when the structural defect was present, depending on the type of polarization (right or left circular). Finally, a clear improvement in the absorption peaks with an increase in the laser parameter is reported. Full article
(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)
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14 pages, 3311 KiB  
Article
Tunable Photonic Band Gaps in Two-Dimensional Bravais–Moiré Photonic Crystal Composed of High-Tc Superconductors
by Hernán A. Gómez-Urrea, José G. Cardona, Miguel E. Mora-Ramos and Carlos A. Duque
Condens. Matter 2023, 8(2), 51; https://doi.org/10.3390/condmat8020051 - 2 Jun 2023
Viewed by 1464
Abstract
In this study, we perform a theoretical study of light propagation properties in two-dimensional square photonic crystals (PCs) following Bravais–Moiré (BM) patterns composed of copper oxide high-temperature superconductors (HTSCs). The BM PCs are made of cylindrical cores formed from the combination of two [...] Read more.
In this study, we perform a theoretical study of light propagation properties in two-dimensional square photonic crystals (PCs) following Bravais–Moiré (BM) patterns composed of copper oxide high-temperature superconductors (HTSCs). The BM PCs are made of cylindrical cores formed from the combination of two square Bravais lattices. The Moiré pattern forms due to a commensurable rotation of one of these lattices with respect to the other. The dielectric function of the superconducting material is modeled by the two-fluid Gorter–Casimir theory. We report on the corresponding gap, the mapping as a function of the radius of dielectric cores, as well as the dispersion relations of TM modes for BM PCs and for the waveguide system built of defect lines within such a crystal. The BM PCs were composed of copper oxide HTSCs, which exhibit large tunability in terms of temperature. Full article
(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)
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13 pages, 12258 KiB  
Article
Narrowband Filters Designed from Hybrid One-Dimensional Periodic/Quasiperiodic Photonic Crystals with a Single Defect Layer
by Waira Murillo-García, Hernán A. Gómez-Urrea, Miguel E. Mora-Ramos and Carlos A. Duque
Condens. Matter 2023, 8(2), 50; https://doi.org/10.3390/condmat8020050 - 29 May 2023
Cited by 2 | Viewed by 1485
Abstract
We report the transmission spectra and electric field amplitudes of electromagnetic modes propagating in hybrid periodic/quasiperiodic multilayer photonic structures in one dimension (1D). We consider the case of the combination of biperiodic Bragg mirror and triperiodic Bragg mirrors with quasiregular (FB, Fibonacci) layered [...] Read more.
We report the transmission spectra and electric field amplitudes of electromagnetic modes propagating in hybrid periodic/quasiperiodic multilayer photonic structures in one dimension (1D). We consider the case of the combination of biperiodic Bragg mirror and triperiodic Bragg mirrors with quasiregular (FB, Fibonacci) layered components. The corresponding hybrid structure (HB) is formed by concatenating BM(N)-FB(M)-BM(N), where N (M) means the number of periods (sequence order) used for the Bragg mirrors (FB) structure. A single defect layer (D) is considered in the middle of two HBs (HB-D-HB). Optimizing the parameters (the order of sequence, number of Bragg mirror layers, thickness, and the refractive index of D) allows us to obtain narrowband filters. The manipulation of these parameters fixes the number of photonic band gaps as well as the position of transmission peaks. The existence of the selectively localized behavior of some optical modes in the structures is discussed. Full article
(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)
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10 pages, 23184 KiB  
Article
Atomic Structure of Mn-Doped CoFe2O4 Nanoparticles for Metal–Air Battery Applications
by Katariina Pussi, Keying Ding, Bernardo Barbiellini, Koji Ohara, Hiroki Yamada, Chuka Onuh, James McBride, Arun Bansil, Ray K. Chiang and Saeed Kamali
Condens. Matter 2023, 8(2), 49; https://doi.org/10.3390/condmat8020049 - 24 May 2023
Viewed by 1773
Abstract
We discuss the atomic structure of cobalt ferrite nanoparticles doped with Mn via an analysis based on combining atomic pair distribution functions with high energy X-ray diffraction and high-resolution transmission electron microscopy measurements. Cobalt ferrite nanoparticles are promising materials for metal–air battery applications. [...] Read more.
We discuss the atomic structure of cobalt ferrite nanoparticles doped with Mn via an analysis based on combining atomic pair distribution functions with high energy X-ray diffraction and high-resolution transmission electron microscopy measurements. Cobalt ferrite nanoparticles are promising materials for metal–air battery applications. Cobalt ferrites, however, generally show poor electronic conductivity at ambient temperatures, which limits their bifunctional catalytic performance in oxygen electrocatalysis. Our study reveals how the introduction of Mn ions promotes the conductivity of the cobalt ferrite electrode. Full article
(This article belongs to the Special Issue Feature Papers from Condensed Matter Editorial Board Members)
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14 pages, 2823 KiB  
Article
A Positron Implantation Profile Estimation Approach for the PALS Study of Battery Materials
by Xin Li, Bernardo Barbiellini, Vito Di Noto, Gioele Pagot, Meiying Zheng and Rafael Ferragut
Condens. Matter 2023, 8(2), 48; https://doi.org/10.3390/condmat8020048 - 22 May 2023
Viewed by 1426
Abstract
Positron annihilation spectroscopy is a powerful probe to investigate the interfaces in materials relevant for energy storage such as Li-ion batteries. The key to the interpretation of the results is the positron implantation profile, which is a spatial function related to the characteristics [...] Read more.
Positron annihilation spectroscopy is a powerful probe to investigate the interfaces in materials relevant for energy storage such as Li-ion batteries. The key to the interpretation of the results is the positron implantation profile, which is a spatial function related to the characteristics of the materials forming the battery. We provide models for the positron implantation profile in a cathode of a Li-ion battery coin cell. These models are the basis for a reliable visualization of multilayer geometries and their interfaces in thin cathodes of lithium-ion batteries. Full article
(This article belongs to the Special Issue New Advances in Condensed Matter Physics)
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21 pages, 2747 KiB  
Article
Thermodynamics in Stochastic Conway’s Game of Life
by Krzysztof Pomorski and Dariusz Kotula
Condens. Matter 2023, 8(2), 47; https://doi.org/10.3390/condmat8020047 - 19 May 2023
Cited by 2 | Viewed by 1705
Abstract
Cellular automata can simulate many complex physical phenomena using the power of simple rules. The presented methodological platform expresses the concept of programmable matter, of which Newton’s laws of motion are an example. Energy is introduced as the equivalent of the “Game of [...] Read more.
Cellular automata can simulate many complex physical phenomena using the power of simple rules. The presented methodological platform expresses the concept of programmable matter, of which Newton’s laws of motion are an example. Energy is introduced as the equivalent of the “Game of Life” mass, which can be treated as the first level of approximation. The temperature presence and propagation was calculated for various lattice topologies and boundary conditions, using the Shannon entropy measure. This study provides strong evidence that, despite the principle of mass and energy conservation not being fulfilled, the entropy, mass distribution, and temperature approach thermodynamic equilibrium. In addition, the described cellular automaton system transitions from a positive to a negative temperature, which stabilizes and can be treated as a signature of a system in equilibrium. The system dynamics is presented for a few species of cellular automata competing for maximum presence on a given lattice with different boundary conditions. Full article
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10 pages, 291 KiB  
Review
Superconductors with a Topological Gap
by Maria Cristina Diamantini
Condens. Matter 2023, 8(2), 46; https://doi.org/10.3390/condmat8020046 - 16 May 2023
Cited by 1 | Viewed by 1100
Abstract
I review a new superconductivity mechanism in which the gap is opened through a topological mechanism and not through the Landau mechanism of spontaneous symmetry breaking. As a consequence, the low-energy effective theory which describes these new superconductors is not the Landau–Ginzburg theory, [...] Read more.
I review a new superconductivity mechanism in which the gap is opened through a topological mechanism and not through the Landau mechanism of spontaneous symmetry breaking. As a consequence, the low-energy effective theory which describes these new superconductors is not the Landau–Ginzburg theory, formulated in terms of a local-order parameter, but a topological-field theory formulated in terms of emerging gauge fields. This new mechanism is realized as global superconductivty in Josephson junction arrays and in thin superconducting films with thicknesses comparable to the superconducting coherence length, which exhibits emergent granularity. Full article
7 pages, 2288 KiB  
Article
Strong-Coupling Behavior of the Critical Temperature of Pb/Ag, Pb/Cu and Pb/Al Nanocomposites Explained by Proximity Eliashberg Theory
by Giovanni Alberto Ummarino
Condens. Matter 2023, 8(2), 45; https://doi.org/10.3390/condmat8020045 - 12 May 2023
Viewed by 1461
Abstract
The experimental critical temperature of the systems of superconducting (Pb) and normal (Ag, Cu and Al) nanoparticles, with a random distribution and sizes less than their respective coherence lengths, is governed by the proximity [...] Read more.
The experimental critical temperature of the systems of superconducting (Pb) and normal (Ag, Cu and Al) nanoparticles, with a random distribution and sizes less than their respective coherence lengths, is governed by the proximity effect, as shown by the experimental data. At first glance, the behavior of the variation in the critical temperature in function of the ratio of volume fractions of the superconducting and the normal metal components seems to suggest a weak coupling behavior for the superconductor. In reality, upon a more careful analysis, using Eliashberg’s theory for the proximity effect, the system instead shows a strong coupling nature. The most interesting thing is that the theory has no free parameters and perfectly explains the behavior of the experimental data just with the assumption in the case of the nanoparticles Ag and Cu, that the value of the density of states at the Fermi level of silver and copper is equal to the value of lead. Full article
(This article belongs to the Section Superconductivity)
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12 pages, 760 KiB  
Article
Quadriexciton Binding Energy in Electron–Hole Bilayers
by Cesare Malosso, Gaetano Senatore and Stefania De Palo
Condens. Matter 2023, 8(2), 44; https://doi.org/10.3390/condmat8020044 - 10 May 2023
Viewed by 1252
Abstract
Excitonic condensation and superfluidity have recently received a renewed attention, due to the fabrication of bilayer systems in which electrons and holes are spatially separated and form stable pairs known as indirect excitons. Dichalcogenides- and graphene-based bilayers are nowadays built and investigated, giving [...] Read more.
Excitonic condensation and superfluidity have recently received a renewed attention, due to the fabrication of bilayer systems in which electrons and holes are spatially separated and form stable pairs known as indirect excitons. Dichalcogenides- and graphene-based bilayers are nowadays built and investigated, giving access to systems with (i) only spin degeneracy and (ii) spin and valley degeneracy. Simulation studies performed in the last decades at T=0 for simple, model electron–hole bilayers, as function of the interlayer distance and in-layer carrier density, have revealed in case (i) the formation of biexcitons in a tiny region of the parameter space and in case (ii) the formation of stable compounds made of four electrons and four holes (quadriexcitons) in a sizable region of the parameter space. Of some interest is the relation of the properties of isolated biexcitons (quadriexcitons) and those of their finite-density counterpart. In fact, the isolated biexciton has been repeatedly studied in the last years with simulations and other techniques. No simulations, instead, are available to our knowledge for the isolated quadriexciton, for which we present here results of the first quantum Monte Carlo (QMC) study. Stability with respect to the dissociation into biexcitons and the pair correlations while varying the interlayer distance d are discussed. Full article
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10 pages, 603 KiB  
Article
Optical Properties of Magnetic Monopole Excitons
by Junhui Cao and Alexey Kavokin
Condens. Matter 2023, 8(2), 43; https://doi.org/10.3390/condmat8020043 - 9 May 2023
Cited by 1 | Viewed by 1490
Abstract
Here we consider theoretically an exciton-like dipole formed by a magnetic monopole and a magnetic antimonopole. This type of quasiparticles may be formed in a magnetic counterpart of a one dimensional semiconductor crystal. We use the familiar Lorentz driven damped harmonic oscillator model [...] Read more.
Here we consider theoretically an exciton-like dipole formed by a magnetic monopole and a magnetic antimonopole. This type of quasiparticles may be formed in a magnetic counterpart of a one dimensional semiconductor crystal. We use the familiar Lorentz driven damped harmonic oscillator model to find the eigenmodes of magnetic monopole dipoles strongly coupled to light. The proposed model allows predicting optical signatures of magnetic monopole excitons in crystals. Full article
(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)
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12 pages, 1433 KiB  
Article
Low-Lying Collective Excitations of Superconductors and Charged Superfluids
by Serghei Klimin, Jacques Tempere and Hadrien Kurkjian
Condens. Matter 2023, 8(2), 42; https://doi.org/10.3390/condmat8020042 - 3 May 2023
Viewed by 1412
Abstract
We investigate theoretically the momentum-dependent frequency and damping of low-lying collective excitations of superconductors and charged superfluids in the BCS–BEC crossover regime. The study is based on the Gaussian pair-and-density fluctuation method for the propagator of Gaussian fluctuations of the pair and density [...] Read more.
We investigate theoretically the momentum-dependent frequency and damping of low-lying collective excitations of superconductors and charged superfluids in the BCS–BEC crossover regime. The study is based on the Gaussian pair-and-density fluctuation method for the propagator of Gaussian fluctuations of the pair and density fields. Eigenfrequencies and damping rates are determined in a mutually consistent nonperturbative way as complex poles of the fluctuation propagator. Particular attention is paid to new features with respect to preceding theoretical studies, which were devoted to collective excitations of superconductors in the far BCS regime. We find that at a sufficiently strong coupling, new branches of collective excitations appear, which manifest different behavior as functions of the momentum and the temperature. Full article
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7 pages, 9258 KiB  
Article
Features of Light-Matter Coupling in Non-Ideal Lattice of Coupled Microcavities Containing Quantum Dots
by Vladimir V. Rumyantsev, Stanislav A. Fedorov, Konstantin V. Gumennyk and Alexey Ye. Rybalka
Condens. Matter 2023, 8(2), 41; https://doi.org/10.3390/condmat8020041 - 2 May 2023
Viewed by 1500
Abstract
In this paper, within the framework of virtual crystal approximation, the mathematical modeling of the dependence of the density of states of polariton excitations in a 1D photonic crystal—a system of pores (tunnel-coupled microresonators) containing quantum dots—on the concentration of structural defects is [...] Read more.
In this paper, within the framework of virtual crystal approximation, the mathematical modeling of the dependence of the density of states of polariton excitations in a 1D photonic crystal—a system of pores (tunnel-coupled microresonators) containing quantum dots—on the concentration of structural defects is performed. Full article
(This article belongs to the Special Issue Physics of Light-Matter Coupling in Nanostructures)
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9 pages, 1467 KiB  
Article
Investigating the Intrinsic Anisotropy of VO2(101) Thin Films Using Linearly Polarized Resonant Photoemission Spectroscopy
by Alessandro D’Elia, Vincent Polewczyk, Aleksandr Yu. Petrov, Liang Li, Chongwen Zou, Javad Rezvani and Augusto Marcelli
Condens. Matter 2023, 8(2), 40; https://doi.org/10.3390/condmat8020040 - 26 Apr 2023
Viewed by 1357
Abstract
VO2 is one of the most studied vanadium oxides because it undergoes a reversible metal-insulator transition (MIT) upon heating with a critical temperature of around 340 K. One of the most overlooked aspects of VO2 is the band’s anisotropy in the [...] Read more.
VO2 is one of the most studied vanadium oxides because it undergoes a reversible metal-insulator transition (MIT) upon heating with a critical temperature of around 340 K. One of the most overlooked aspects of VO2 is the band’s anisotropy in the metallic phase when the Fermi level is crossed by two bands: π* and d||. They are oriented perpendicularly in one respect to the other, hence generating anisotropy. One of the parameters tuning MIT properties is the unbalance of the electron population of π* and d|| bands that arise from their different energy position with respect to the Fermi level. In systems with reduced dimensionality, the electron population disproportion is different with respect to the bulk leading to a different anisotropy. Investigating such a system with a band-selective spectroscopic tool is mandatory. In this manuscript, we show the results of the investigation of a single crystalline 8 nm VO2/TiO2(101) film. We report on the effectiveness of linearly polarized resonant photoemission (ResPES) as a band-selective technique probing the intrinsic anisotropy of VO2. Full article
(This article belongs to the Special Issue Superstripes Physics)
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17 pages, 6567 KiB  
Article
Superconducting Stiffness and Coherence Length of FeSe0.5Te0.5 Measured in a Zero-Applied Field
by Amotz Peri, Itay Mangel and Amit Keren
Condens. Matter 2023, 8(2), 39; https://doi.org/10.3390/condmat8020039 - 23 Apr 2023
Cited by 1 | Viewed by 2030
Abstract
Superconducting stiffness ρs and coherence length ξ are usually determined by measuring the penetration depth λ of a magnetic field and the upper critical field Hc2 of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could [...] Read more.
Superconducting stiffness ρs and coherence length ξ are usually determined by measuring the penetration depth λ of a magnetic field and the upper critical field Hc2 of a superconductor (SC), respectively. However, in magnetic SC, which is iron-based, this could lead to erroneous results, since the internal field could be very different from the applied one. To overcome this problem in Fe1+ySexTe1x with x0.5 and y0 (FST), we measured both quantities with the Stiffnessometer technique. In this technique, one applies a rotor-free vector potential A to a superconducting ring and measures the current density j via the ring’s magnetic moment m. ρs and ξ are determined from London’s equation, j=ρsA, and its range of validity. This method is particularly accurate at temperatures close to the critical temperature Tc. We find weaker ρs and longer ξ than existing literature reports, and critical exponents which agree better with expectations based on the Ginzburg–Landau theory. Full article
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10 pages, 4219 KiB  
Article
Anodic Potential and Conversion Chemistry of Anhydrous Iron (II) Oxalate in Na-Ion Batteries
by Vasilii Gromov, Atlas Noubir, Fatemeh Keshavarz, Ekaterina Laakso, Bernardo Barbiellini and Arun Bansil
Condens. Matter 2023, 8(2), 38; https://doi.org/10.3390/condmat8020038 - 23 Apr 2023
Viewed by 1660
Abstract
Anhydrous ferrous (II) oxalate (AFO) outperforms its hydrated form when used as an anode material in Li-ion batteries (LIBs). With the increasing interest in Na-ion batteries (NIBs) in mind, we examine the potential of AFO as the anode in NIBs through first principles [...] Read more.
Anhydrous ferrous (II) oxalate (AFO) outperforms its hydrated form when used as an anode material in Li-ion batteries (LIBs). With the increasing interest in Na-ion batteries (NIBs) in mind, we examine the potential of AFO as the anode in NIBs through first principles calculations involving both periodic and non-periodic structures. Our analysis based on periodic (non-periodic) modeling scheme shows that the AFO anode generates a low reaction potential of 1.22 V (1.45 V) in the NIBs, and 1.34 V (1.24 V) in the LIBs, which is much lower than the potential of NIBs with mixed oxalates. The conversion mechanism in the underlying electrochemical process involves the reduction of Fe2+ with the addition of Na or Li. Such conversion electrodes can achieve high capacities through the Fe2+ valence states of iron. Full article
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54 pages, 14108 KiB  
Review
Advanced Boron Carbide Matrix Nanocomposites Obtained from Liquid-Charge: Focused Review
by Levan Chkhartishvili, Archil Mikeladze, Otar Tsagareishvili, Vakhtang Kvatchadze, Valery Tavkhelidze, Zviad Mestvirishvili, Dimitri Driaev, Natia Barbakadze, Lili Nadaraia, Ketevan Sarajishvili, Irma Jinikashvili, Manana Buzariashvili and Roin Chedia
Condens. Matter 2023, 8(2), 37; https://doi.org/10.3390/condmat8020037 - 20 Apr 2023
Cited by 5 | Viewed by 2620
Abstract
Boron carbide is known as a hard material; it possesses a unique complex of physical-mechanical properties and has diverse applications in industries. An expansion of its field of uses stems from the creation of boron carbide matrix nanocomposite materials. In view of this [...] Read more.
Boron carbide is known as a hard material; it possesses a unique complex of physical-mechanical properties and has diverse applications in industries. An expansion of its field of uses stems from the creation of boron carbide matrix nanocomposite materials. In view of this perspective, an effective liquid-charge synthesizing method for their components in nanopowder form has been proposed. This paper provides a focused review on advanced boron carbide matrix ceramic and metal-ceramic nanocomposites recently obtained by the authors using this method. Particular attention is paid to the characterization of boron carbide nanocomposites, including some ceramic borides, metallic alloys and also other metal-ceramic composites. Full article
(This article belongs to the Special Issue Advances in Nanocomposite Materials)
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12 pages, 754 KiB  
Article
Superconducting Diode Effect in Topological Hybrid Structures
by Tairzhan Karabassov, Emir S. Amirov, Irina V. Bobkova, Alexander A. Golubov, Elena A. Kazakova and Andrey S. Vasenko
Condens. Matter 2023, 8(2), 36; https://doi.org/10.3390/condmat8020036 - 14 Apr 2023
Cited by 8 | Viewed by 2223
Abstract
Currently, the superconducting diode effect (SDE) is being actively discussed, due to its large application potential in superconducting electronics. In particular, superconducting hybrid structures, based on three-dimensional (3D) topological insulators, are among the best candidates, due to their having the strongest spin–orbit coupling [...] Read more.
Currently, the superconducting diode effect (SDE) is being actively discussed, due to its large application potential in superconducting electronics. In particular, superconducting hybrid structures, based on three-dimensional (3D) topological insulators, are among the best candidates, due to their having the strongest spin–orbit coupling (SOC). Most theoretical studies on the SDE focus either on a full numerical calculation, which is often rather complicated, or on the phenomenological approach. In the present paper, we compare the linearized and nonlinear microscopic approaches in the superconductor/ferromagnet/3D topological insulator (S/F/TI) hybrid structure. Employing the quasiclassical Green’s function formalism we solve the problem self-consistently. We show that the results obtained by the linearized approximation are not qualitatively different from the nonlinear solution. The main distinction in the results between the two methods was quantitative, i.e., they yielded different supercurrent amplitudes. However, when calculating the so-called diode quality factor the quantitative difference is eliminated and both approaches result in good agreement. Full article
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7 pages, 2421 KiB  
Project Report
Effects of Focused Ion Beam Lithography on La2−xSrxCuO4 Single Crystals
by Roberta Caruso, Fernando Camino, Genda Gu, John M. Tranquada, Myung-Geun Han, Yimei Zhu, Anthony T. Bollinger and Ivan Božović
Condens. Matter 2023, 8(2), 35; https://doi.org/10.3390/condmat8020035 - 13 Apr 2023
Cited by 1 | Viewed by 1531
Abstract
Focused ion beam (FIB) milling is a mask-free lithography technique that allows the precise shaping of 3D materials on the micron and sub-micron scale. The recent discovery of electronic nematicity in La2−xSrxCuO4 (LSCO) thin films triggered the [...] Read more.
Focused ion beam (FIB) milling is a mask-free lithography technique that allows the precise shaping of 3D materials on the micron and sub-micron scale. The recent discovery of electronic nematicity in La2−xSrxCuO4 (LSCO) thin films triggered the search for the same phenomenon in bulk LSCO crystals. With this motivation, we have systematically explored FIB patterning of bulk LSCO crystals into micro-devices suitable for longitudinal and transverse resistivity measurements. We found that several detrimental factors can affect the result, ultimately compromising the possibility of effectively using FIB milling to fabricate sub-micrometer LSCO devices, especially in the underdoped regime. Full article
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10 pages, 3164 KiB  
Article
Plasma-Assisted Nitrogen Doping of Langmuir–Blodgett Self-Assembled Graphene Films
by Tijana Tomašević-Ilić, Nikola Škoro, Đorđe Jovanović, Nevena Puač and Marko Spasenović
Condens. Matter 2023, 8(2), 34; https://doi.org/10.3390/condmat8020034 - 4 Apr 2023
Viewed by 1793
Abstract
Graphene films prepared from solution and deposited by Langmuir–Blodgett self-assembly technique (LBSA) were treated with radio-frequency (13.56 MHz) nitrogen plasma in order to investigate the influence of the time of nitrogen plasma exposure on the work function, sheet resistance, and surface morphology of [...] Read more.
Graphene films prepared from solution and deposited by Langmuir–Blodgett self-assembly technique (LBSA) were treated with radio-frequency (13.56 MHz) nitrogen plasma in order to investigate the influence of the time of nitrogen plasma exposure on the work function, sheet resistance, and surface morphology of LBSA graphene films. Kelvin probe force microscopy and sheet resistance measurements confirm nitrogen functionalization of our films, with the Fermi level shifting in a direction that indicates binding to a pyridinic and/or pyrrolic site. Upon 1 min of nitrogen plasma exposure, the sheet resistance decreases and there is no obvious difference in film morphology. However, plasma exposure longer than 5 min leads to the removal of graphene flakes and degradation of graphene films, in turn, affecting the flake connectivity and increasing film resistance. We show that by changing the exposure time, we can control the work function and decrease sheet resistance, without affecting surface morphology. Controllability of the plasma technique has an advantage for graphene functionalization over conventional doping techniques such as chemical drop-casting. It allows for the controllable tuning of the work function, surface morphology, and sheet resistance of LBSA graphene films, which is substantial for applications in various optoelectronic devices. Full article
(This article belongs to the Section Surface and Interfaces)
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10 pages, 1003 KiB  
Article
Elucidation of Spin-Correlations, Fermi Surface and Pseudogap in a Copper Oxide Superconductor
by Hiroshi Kamimura, Masaaki Araidai, Kunio Ishida, Shunichi Matsuno, Hideaki Sakata, Kenji Sasaoka, Kenji Shiraishi, Osamu Sugino, Jaw-Shen Tsai and Kazuyoshi Yamada
Condens. Matter 2023, 8(2), 33; https://doi.org/10.3390/condmat8020033 - 4 Apr 2023
Cited by 1 | Viewed by 1864
Abstract
First-principles calculations for underdoped La2−xSrxCuO4 (LSCO) have revealed a Fermi surface consisting of spin-triplet (KS) particles at the antinodal Fermi-pockets and spin-singlet (SS) particles at the nodal Fermi-arcs in the presence of AF local order. By performing [...] Read more.
First-principles calculations for underdoped La2−xSrxCuO4 (LSCO) have revealed a Fermi surface consisting of spin-triplet (KS) particles at the antinodal Fermi-pockets and spin-singlet (SS) particles at the nodal Fermi-arcs in the presence of AF local order. By performing a unique method of calculating the electronic-spin state of overdoped LSCO and by measurement of the spin-correlation length by neutron inelastic scattering, the origin of the phase-diagram, including the pseudogap phase in the high temperature superconductor, Sr-doped copper-oxide LSCO, has been elucidated. We have theoretically solved the long-term problem as to why the angle-resolved photoemission spectroscopy (ARPES) has not been able to observe Fermi pockets in the Fermi surface of LSCO. As a result, we show that the pseudogap region is bounded below the characteristic temperature T*(x) and above the superconducting transition temperature Tc(x) in the T vs. x phase diagram, where both the AF order and the KS particles in the Fermi pockets vanish at T*(x), whilst KS particles contribute to d-wave superconductivity below Tc. We also show that the relationship T*(xc) = Tc(xc) holds at xc = 0.30, which is consistent with ARPES experiments. At T*(x), a phase transition occurs from the pseudogap phase to an unusual metallic phase in which only the SS particles exist. Full article
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11 pages, 1357 KiB  
Article
Angle-dependent Magnetoresistance of an Ordered Bose Glass of Vortices in YBa2Cu3O7-δ Thin Films with a Periodic Pinning Lattice
by Bernd Aichner, Lucas Backmeister, Max Karrer, Katja Wurster, Reinhold Kleiner, Edward Goldobin, Dieter Koelle and Wolfgang Lang
Condens. Matter 2023, 8(2), 32; https://doi.org/10.3390/condmat8020032 - 27 Mar 2023
Cited by 1 | Viewed by 2014
Abstract
The competition between intrinsic disorder in superconducting YBa2Cu3O7δ (YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples [...] Read more.
The competition between intrinsic disorder in superconducting YBa2Cu3O7δ (YBCO) thin films and an ultradense triangular lattice of cylindrical pinning centers spaced at 30 nm intervals results in an ordered Bose glass phase of vortices. The samples were created by scanning the focused beam of a helium-ion microscope over the surface of the YBCO thin film to form columns of point defects where superconductivity was locally suppressed. The voltage–current isotherms reveal critical behavior and scale in the vicinity of the second-order glass transition. The latter exhibits a distinct peak in melting temperature (Tg) vs. applied magnetic field (Ba) at the magnetic commensurability field, along with a sharp rise in the lifetimes of glassy fluctuations. Angle-dependent magnetoresistance measurements in constant-Lorentz-force geometry unveil a strong increase in anisotropy compared to a pristine reference film where the density of vortices matches that of the columnar defects. The pinning is therefore, dominated by the magnetic-field component parallel to the columnar defects, exposing its one-dimensional character. These results support the idea of an ordered Bose glass phase. Full article
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7 pages, 1407 KiB  
Article
Pump-Probe X-ray Photoemission Spectroscopy of Free-Standing Graphane
by Roberto Costantini, Dario Marchiani, Maria Grazia Betti, Carlo Mariani, Samuel Jeong, Yoshikazu Ito, Alberto Morgante and Martina Dell’Angela
Condens. Matter 2023, 8(2), 31; https://doi.org/10.3390/condmat8020031 - 27 Mar 2023
Cited by 1 | Viewed by 1896
Abstract
Free-standing nanoporous graphene was hydrogenated at about 60 at.% H uptake, as determined by the emerging of the sp3 bonding component in the C 1s core level investigated by high-resolution X-ray photoelectron spectroscopy (XPS). Fully unsupported graphane was investigated by XPS under [...] Read more.
Free-standing nanoporous graphene was hydrogenated at about 60 at.% H uptake, as determined by the emerging of the sp3 bonding component in the C 1s core level investigated by high-resolution X-ray photoelectron spectroscopy (XPS). Fully unsupported graphane was investigated by XPS under optical excitation at 2.4 eV. At a laser fluence of 1.6 mJ/cm2, a partial irreversible dehydrogenation of the graphane was observed, which could be attributed either to the local temperature increase or to a photo-induced softening of the H-to-C stretching mode. The sub-ns dynamics of the energy shift and peak broadening of the C 1s core level revealed two different decay constants: 210 ps and 130 ps, respectively, the former associated with photovoltage dynamics and the latter with thermal heating on a time scale comparable with the synchrotron temporal resolution. Full article
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8 pages, 310 KiB  
Article
FL* Interpretation of a Dichotomy in the Spin Susceptibility of the Cuprates
by Pieralberto Marchetti
Condens. Matter 2023, 8(2), 30; https://doi.org/10.3390/condmat8020030 - 23 Mar 2023
Cited by 1 | Viewed by 1167
Abstract
We propose that some dichotomic Fermi liquid versus non-Fermi liquid behaviours of physical quantities in hole-doped cuprates can be explained in terms of the FL* fractionalized Fermi liquid concept, introduced some years ago, even beyond the region of underdoping. The particle excitations of [...] Read more.
We propose that some dichotomic Fermi liquid versus non-Fermi liquid behaviours of physical quantities in hole-doped cuprates can be explained in terms of the FL* fractionalized Fermi liquid concept, introduced some years ago, even beyond the region of underdoping. The particle excitations of this FL* system are the holon carrying charge, the spinon carrying spin 1/2, gauge fluctuations coupling them and the hole as a spinon–holon bound state or resonance due to gauge binding. In our proposal, physical responses have a Fermi-liquid-type behaviour if they are dominated by the hole resonance, whereas a non-Fermi liquid behaviour appears if they are dominated by spinon–spinon (and possibly also holon–holon) gauge interactions. The specific case of spin susceptibility in the so-called "strange metal phase" is discussed. The uniform susceptibility turns out to be hole-dominated, the spin-lattice relaxation rate in the Cu sites is spinon-dominated. Full article
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