Condensed Matter

8 pages, 1555 KiB

Open AccessArticle

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

by Huanyou Wang, Guangqi Xie and Yingying Zhan

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

In this study, the curvature changes of an unintentionally doped GaN end and third quantum well were observed in situ when the annealing times of a GaN buffer layer were 40 s, 50 s and 55 s, respectively. When the annealing time was [...] Read more.

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

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13 pages, 751 KiB

Open AccessArticle

Effect of t_2g-Correlations and Doping in CrSBr Ferromagnetic Semiconductor

by Luis Craco and Sabrina Silva Carara

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

Viewed by 148

Abstract

We perform a comprehensive analysis of the correlated electronic structure reconstruction of the ferromagnetic CrSBr van der Waals (vdW) bulk crystal. Using generalized gradient approximation combined with dynamical mean-field theory, we show the minor role played by multi-orbital electron–electron interactions in semiconducting CrSBr. [...] Read more.

We perform a comprehensive analysis of the correlated electronic structure reconstruction of the ferromagnetic CrSBr van der Waals (vdW) bulk crystal. Using generalized gradient approximation combined with dynamical mean-field theory, we show the minor role played by multi-orbital electron–electron interactions in semiconducting CrSBr. Our study is relevant to understanding the electronic structure within the

{C r}^{3 +}

oxidation state with strongly spin-polarized

t_{2 g}

orbitals and should be applicable to other ferromagnetic vdW materials from bulk down to the low-dimensional limit. This work is relevant for understanding orbital and spin selectivity and its link to the memristor current–voltage characteristic of CrSBr for future neuromorphic computing. Full article

(This article belongs to the Section Condensed Matter Theory)

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18 pages, 23429 KiB

Open AccessArticle

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

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

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

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Abstract

Thin films of monomeric species polythiophene (PTh), poly-(3,4-ethylenedioxythiophene) (PEDOT), and the copolymer PTh/PEDOT were prepared through electropolymerization and deposited above fluorine-doped tin oxide (FTO) substrates. The functional groups of the monomeric species (PTh, PEDOT) and polymeric species (PTh/PEDOT) were characterized by Fourier-transform infrared [...] Read more.

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

(This article belongs to the Section Surface and Interfaces)

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3 pages, 145 KiB

Open AccessEditorial

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

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

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

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Abstract

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

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

3 pages, 123 KiB

Open AccessEditorial

In-Depth Experimental and Computational Studies on Rechargeable Battery Materials

by Jan Kuriplach and Rolando Saniz

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

Viewed by 110

Abstract

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

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

8 pages, 512 KiB

Open AccessArticle

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

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

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

Viewed by 131

Abstract

Within the framework of Dexter’s theory, we calculate the energies of the Stark levels of Yb³⁺-Yb³⁺ paired centers in lithium niobate doped with Yb³⁺ ions (LiNbO₃:Yb³⁺) crystal, considering the interaction of optical electrons of ytterbium [...] Read more.

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

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24 pages, 3710 KiB

Open AccessReview

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

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

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

Viewed by 290

Abstract

In recent years, significant effort was made to make the 3D printing of fully dense rare-earth permanent magnets a reality. Since suitable Nd₂Fe₁₄B-based initial powder material became available, additive manufacturing implementation spread widely, which led to many studies being [...] Read more.

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

(This article belongs to the Section Magnetism)

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29 pages, 10332 KiB

Open AccessReview

Basic Aspects of Ferroelectricity Induced by Noncollinear Alignment of Spins

by I. V. Solovyev

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

Viewed by 477

Abstract

Basic principles of ferroelectric activity induced by the noncollinear alignment of spins are reviewed. There is a fundamental reason why the inversion symmetry can be broken by certain magnetic order. This situation occurs when the magnetic order simultaneously involves ferromagnetic (

F

) [...] Read more.

Basic principles of ferroelectric activity induced by the noncollinear alignment of spins are reviewed. There is a fundamental reason why the inversion symmetry can be broken by certain magnetic order. This situation occurs when the magnetic order simultaneously involves ferromagnetic (

F

) and antiferromagnetic (

A

) counterparts, transforming under the spatial inversion

I

and time reversal

T

as

I F = F

and

IT A = A

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

\vec{P}

. The noncollinear alignment of spins is one of examples of such coexistence of

F

and

A

. This coexistence principle imposes a constraint on possible dependencies of

\vec{P}

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

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

, and “single-ion anisotropy”,

e_{i} \cdot

\vec{Π}

e_{i}

. Microscopically,

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

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

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

, where

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

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

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

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

\vec{P}

even in centrosymmetric crystals. The symmetry properties of

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

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

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

(

{\vec{ϵ}}_{j i}

being the direction of the bond

i j

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

\frac{1}{2}

or if magnetic ions are located in inversion centers, thus severely restricting the applicability of this microscopic mechanism. The properties of multiferroic materials are reconsidered from the viewpoint of these principles. A particular attention is paid to complications caused by possible deviations from the KNB rule. Full article

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14 pages, 991 KiB

Open AccessReview

Emergent Magnetic Monopoles in Quantum Matter

by Maria Cristina Diamantini

Condens. Matter 2025, 10(2), 20; https://doi.org/10.3390/condmat10020020 - 1 Apr 2025

Viewed by 267

Abstract

Magnetic monopoles, though elusive as elementary particles, emerge as quantum excitations in granular quantum materials. Under certain conditions, they can undergo Bose condensation, leading to the formation of a novel state of matter known as the superinsulator. In this state, charge carriers, Cooper [...] Read more.

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

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

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Condens. Matter, Volume 10, Issue 2 (June 2025) – 9 articles

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