Materials Science
Biaxial Strain Control of Helimagnetism via Chemical Expansion in Thin Film SrFeO3
Jennifer Fowlie, Jiarui Li, Danilo Puggioni et al. (+15 more)
We demonstrate control of helimagnetic order in biaxially strained SrFeO3 thin films using
neutron diffraction and resonant soft x-ray scattering. SrFeO3, a negative charge-transfer
oxide, exhibits a complex
magnetic phase diagram that includes multi-q
spin structures. Tensile epitaxial strain produces a pronounced shortening of the helimagnetic ordering length and a tilting of the
magnetic ordering vector. We interpret this behavior in terms of chemical expansion:
lattice dilation under tensile strain lowers the energetic cost of oxygen vacancies, leading to an expanded unit
cell that modifies Fe-O hybridization and enhances superexchange relative to double exchange. These results reveal how epitaxial strain can indirectly tune helimagnetism through defect-driven chemical expansion, highlighting the strong coupling between
lattice, chemistry, and
magnetic order in transition-metal
oxides. Our findings establish chemical expansion as an effective mechanism for engineering complex
magnetic textures in
oxide thin films, with implications for spintronic, magnonic, and
quantum information applications.
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All authors Jennifer Fowlie, Jiarui Li, Danilo Puggioni, Lucas Barreto, Lin Ding Yuan, James M. Rondinelli, Ronny Sutarto, Teak D. Boyko, Fabio Orlandi, Pascal Manuel, Dmitry Khalyavin, Eder G. Lomeli, Brian Moritz, Thomas P. Devereaux, Skylar Koroluk, Robert J. Green, Steven J. May, Harold Y. Hwang
Materials Science
Self-pinning mechanism for grain boundary stabilization
Omar Hussein and Yuri Mishin
Previous research focused on two different mechanisms of microstructure stabilization in
alloys: thermodynamic stabilization by reducing the grain boundary (GB) free energy and kinetic stabilization by suppressing the GB mobility by solute drag or embedded pinning particles. Here, we propose a new GB stabilization mechanism, called self-pinning, in which the segregation atmosphere of a moving GB spontaneously breaks into solute-rich clusters, which produce a strong pinning effect in addition to the free energy reduction resulting from the segregation. The cluster formation is caused by strong solute-solute attraction at GBs, leading to a first-order transformation between solute-lean and solute-rich GB phases. The effect is demonstrated by kinetic Monte Carlo simulations capturing segregation thermodynamics, GB dynamics, and solute
diffusion. The self-pinning provides an intrinsic stabilization mechanism for suppressing grain growth that couples thermodynamics and kinetics. The mechanism obviates the need for pre-existing second phase inclusions, refocusing the
alloy design on GB phase behavior.
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Materials Science
Benchmarking of Massively Parallel Phase-Field Codes for Directional Solidification
Jiefu Tian, David Montiel, Kaihua Ji et al. (+4 more)
We present a detailed
benchmark comparing two state-of-the-art phase-field implementations for simulating
alloy solidification under experimentally relevant conditions. The study investigates the directional solidification of Al-3wt%Cu under high-velocity solidification conditions and SCN-0.46wt% camphor under microgravity conditions from National Aeronautics and Space Administration (NASA) DECLIC-DSI-R experiments. Both codes, one employing finite-difference discretization with uniform mesh and GPU-acceleration (GPU-PF) and the other one employing finite-element discretization with adaptive-mesh and CPU-parallelization (PRISMS-PF), solve the same quantitative phase-field formulation that incorporates an anti-trapping current for the solidification of dilute
alloys. We evaluate the predictions of each code for dendritic morphology, primary spacing, and tip dynamics in both 2D and 3D, as well as their numerical convergence and computational performance. While existing
benchmark problems have primarily focused on simplified or small-scale simulations, they do not reflect the computational and modeling challenges posed by employing experimentally relevant time and length scales. Our results provide a practical framework for assessing phase-field code performance as well as validating and facilitating their application in integrated computational materials engineering (ICME) workflows that require integration with realistic experimental data.
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All authors Jiefu Tian, David Montiel, Kaihua Ji, Trevor Lyons, Jason Landini, Katsuyo Thornton, Alain Karma
Materials Science
Device Applications of Heterogeneously Integrated Strain-Switched Ferrimagnets/Topological Insulator/Piezoelectric Stacks
Supriyo Bandyopadhyay
A family of ferrimagnets (CoV2O4, GdCo, TbCo) exhibits out-of-plane
magnetic anisotropy when strained compressively and in-plane
magnetic anisotropy when strained expansively (or vice versa). If such a ferrimagnetic thin film is placed on top of a topological
insulator (TI) thin film and its
magnetic anisotropy is modulated with strain, then interfacial exchange coupling between the ferrimagnet (FM) and the underlying TI will modulate the surface current flowing through the latter. If the strain is varied continuously, the current will also vary continuously and if the strain alternates in time, the current will also alternate with the frequency of the strain modulation, as long as the frequency is not so high that the period is smaller than the switching time of the FM. If the strain is generated with a gate voltage by integrating a piezoelectric underneath the FM/TI stack, then that can implement a transconductance amplifier or a synapse for neuromorphic computation.
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Materials Science · Cross-listed from cond-mat.str-el
Atomically-sharp magnetic soliton in the square-net lattice EuRhAl$_{4}$Si$_{2}$
Kevin Allen, Juba Bouaziz, Yichen Zhang et al. (+17 more)
Topological
spin textures are hallmark manifestations of competing interactions in
magnetic matter. Their effective description by nonlinear field theories reflects an energetic frustration that destabilizes uniform order while selecting finite-size, topologically nontrivial configurations as stationary states. Among the most extreme realizations are atomically-sharp domain wall excitations, namely one-dimensional (1D)
magnetic solitons, which represent the ultimate scaling limit of
magnetic textures. Such
solitons may emerge in
magnetic systems where effective exchange interactions compete directly with uniaxial
magnetic anisotropy. Here we show that the square-net rare earth compound EuRhAl$_{4}$Si$_{2}$ realizes a very susceptible regime where the
magnetic anisotropy competes with highly frustrated exchange interactions stabilizing a rare ferrimagnetic $\uparrow\uparrow\downarrow$ state that, under applied
magnetic field, supports the formation of atomically-sharp
soliton defects. We confirm the bulk response of the 1D
magnetic solitons via magnetization and electrical transport measurements. We establish both the zero- and in-field $\uparrow\uparrow\downarrow$ order via
neutron diffraction, while
magnetic force microscopy visualizes its real-space
evolution into a stripe-like array. To elucidate the microscopic origin of the
soliton, we relate the Ruderman-Kittel-Kasuya-Yosida (RKKY)-driven exchange interactions and the
magnetic anisotropy through density functional theory, and we construct an effective 1D $J_{1}$-$J_{2}$-$K$ model whose atomistic
spin dynamics simulations reproduce the observed
soliton states as a function of external field. Our results demonstrate that EuRhAl$_{4}$Si$_{2}$ hosts atomically-sharp, field-driven 1D
magnetic solitons, providing a new platform for studying 1D topological excitations at the atomic length scale.
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All authors Kevin Allen, Juba Bouaziz, Yichen Zhang, Kai Du, Sanu Mishra, Gustav Bihlmayer, Yiqing Hao, Victor Ukleev, Chen Luo, Florin Radu, Yuxiang Gao, Marta Zonno, Sergey Gorovikov, Christopher Lane, Jian-Xin Zhu, Huibo Cao, Sang-Wook Cheong, Ming Yi, Stefan Blügel, Emilia Morosan
Materials Science
Computational discovery of cathode materials for rechargeable aqueous zinc-ion batteries
Caio Miranda Miliante, Yuzhen Deng, Brian D. Adams et al. (+2 more)
Rechargeable aqueous zinc-ion batteries (RAZIBs) attract major interest for deployment in grid-scale energy storage due to higher safety and lower cost when compared to lithium-ion batteries. However, currently studied cathode materials suffer from capacity fade when cycling at rates appropriate for grid-scale applications ($<$ C/2). To address the present limitation on cathode material availability, more than 2000 previously synthesized
oxides, chalcogenides, Prussian blue analogues, and polyanion materials were computationally screened for the discovery of highly stable RAZIB cathode materials. The structural, electrochemical, and chemical properties of the materials were respectively evaluated through an investigation of the available Zn$^{2+}$ percolation paths, the stability of the material in aqueous media under RAZIB operation conditions, and the attained transition metal oxidation state during cycling. The transition metal oxidation state and intercalating ion coordination environment were determined to govern the magnitude of the calculated Zn$^{2+}$ intercalation potential, with this finding guiding the development of batteries with high operation voltages. 12 materials previously unexplored as cathodes for RAZIBs were identified to have promising operational properties as cathodes, such as high Zn$^{2+}$ (de)intercalation potential, electrochemical stability, theoretical gravimetric capacity, and energy density. Finally, $\alpha$-FePO$_{4}$ was experimentally tested as a RAZIB cathode, with a main redox peak observed from cyclic voltammetry matching previous results for amorphous FePO$_{4}$ as a cathode for RAZIB. However, the subpar charge storage performance highlights the necessity of further experimental investigations. Overall, the materials identified in this study present a guide for the experimental development of stable next-generation cathode materials for RAZIBs.
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All authors Caio Miranda Miliante, Yuzhen Deng, Brian D. Adams, Drew Higgins, Oleg Rubel
Materials Science
Semiclassical Routes to the $\alpha$-RuCl$_3$ Scattering Continuum via Model Meta$-$Analysis
Chaebin Kim and Martin Mourigal
$\alpha$-RuCl$_3$ is a leading material for proximate Kitaev magnetism. We address the origin of the broad, $\Gamma$-point centered excitation continuum observed by inelastic
neutron scattering at elevated temperatures in this compound. Using
stochastic Landau-Lifshitz dynamics augmented with
quantum-equivalent corrections, we reproduce the temperature-dependent dynamical
spin structure factor across both the correlated and conventional paramagnetic regimes. A meta-analysis of 38 published exchange parameter sets identifies those most consistent with the full temperature
evolution. A
Bayesian optimization procedure is used to derive parameters that capture the low-energy
star-like momentum dependence and the overall bandwidth of the continuum. Rescaling temperatures by the Curie–Weiss scale produces a collapse of spectral measures, demonstrating that the high-$T$ dynamics are governed by correlated paramagnetism below $\theta_{\mathrm{CW}}$ rather than by the Kitaev crossover to fractionalized excitations. Complementary 24-site exact diagonalization clarifies finite-size systematics at low temperature and the proximity to zigzag/incommensurate ordering. Beyond $\alpha$-RuCl$_3$, our simulation pipeline provides a reproducible, data-driven framework to infer effective
spin models in magnets that exhibit broad continua.
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Materials Science
PySlice: Routine Vibrational Electron Energy Loss Spectroscopy Prediction with Universal Interatomic Potentials
Harrison A. Walker, Thomas W. Pfeifer, Paul M. Zeiger et al. (+3 more)
Vibrational spectroscopy in the electron microscope can reveal
phonon excitations with nanometer spatial resolution, yet routine prediction remains out of reach due to fragmented workflows requiring specialized expertise. Here we introduce PySlice, the first publicly available implementation of the Time Autocorrelation of Auxiliary Wavefunction (TACAW) method, providing an automated framework that produces momentum- and energy-resolved vibrational electron energy-loss spectra directly from atomic structures. By integrating universal machine learning interatomic potentials with TACAW, PySlice eliminates the bottleneck of per-system potential development. Users input atomic structures and obtain
phonon dispersions, spectral diffraction patterns, and spectrum images through a unified workflow spanning molecular dynamics, GPU-accelerated electron scattering, and frequency-domain analysis. We outline the formulation behind the code, demonstrate its application to canonical systems in materials science, and discuss its use for advanced analysis and materials exploration. The modular Python architecture additionally supports conventional electron microscopy simulations, providing a general-purpose platform for imaging and diffraction calculations. PySlice makes vibrational spectroscopy prediction routine rather than specialized, enabling computational screening for experimental design, systematic exploration of
phonon physics across materials families, and high-throughput generation of simulated data for training of future machine learning models.
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All authors Harrison A. Walker, Thomas W. Pfeifer, Paul M. Zeiger, Jordan A. Hachtel, Sokrates T. Pantelides, Eric R. Hoglund
Materials Science
Multiscale Modeling of Metal/Oxide/Metal Conductive Bridging Random Access Memory Cells: from Ab Initio to Finite Element Calculations
Jan Aeschlimann, Fabian Durch, Christoph Weilenmann et al. (+3 more)
We present a multiscale simulation framework to compute the current vs. voltage (I-V ) characteristics of metal/
oxide/metal structures building the core of conductive bridging random access
memory (CBRAM)
cells and to shed light on their resistance switching properties. The approach relies on a finite element model whose input material parameters are extracted either from ab initio or from machine-learned empirical calculations. The applied techniques range from molecular dynamics and nudged elastic band to electronic and thermal
quantum transport. Such an approach drastically reduces the number of fitting parameters needed and makes the resulting modeling environment more accurate than traditional ones. The developed computational framework is then applied to the investigation of an Ag/a-SiO2/Pt CBRAM, reproducing experimental data very well. Moreover, the relevance of Joule heating is assessed by considering various
cell geometries. It is found that self-heating manifests itself in devices with thin conductive filaments with few-nanometer diameters and at current concentrations in the 10s-microampere range. With the proposed methodology it is now possible to explore the potential of not-yet fabricated
memory cells and to reliably optimize their design.
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All authors Jan Aeschlimann, Fabian Durch, Christoph Weilenmann, Alexandros Emboras, Mathieu Luisier, Juerg Leuthold
Materials Science
Relativistic Effects in LaBi$_2$ Thin Films
Reiley Dorrian, Sungmin Song, Jinwoong Kim et al. (+4 more)
Chemical substitution in crystalline
quantum materials is a powerful way to explore the consequences of strong
spin-orbit coupling on their structural and electronic properties. In this work, we present an investigation of thin films of the La$\textit{Pn}_2$ ($\textit{Pn}$~=~Sb, Bi) class of layered square-net intermetallics. We report the growth of LaBi$_2$ with a pristine layer-by-layer growth mode, classifying it as a good metal displaying superconductivity at $\sim$0.55~K. Compared to LaSb$_2$, we attribute the enhanced metallic behavior and improved growth dynamics of LaBi$_2$ to significant relativistic corrections to its electronic band structure and the resulting impact on both surface energy and intrinsic
phonon scattering.
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All authors Reiley Dorrian, Sungmin Song, Jinwoong Kim, Mizuki Ohno, Seung-Hoon Jhi, Nicholas Kioussis, Joseph Falson
Materials Science
Long-Range Machine Learning of Electron Density for Twisted Bilayer Moiré Materials
Zekun Lou, Alan M. Lewis and Mariana Rossi
Moiré superlattices in two-dimensional (2D) materials exhibit rich
quantum phenomena, but ab initio modelling of these systems remains computationally prohibitive. Existing machine learning methods for accelerating density-functional theory (DFT) can target the prediction of different quantities and often rely on the locality assumption. Here we train a Gaussian process regression SALTED model exclusively on the electron densities of small displaced
bilayer structures and then extrapolate electron density prediction to the large supercells required to describe small twist angles between these
bilayers. We show the necessity of long-range descriptors to yield reliable band structures and electrostatic properties of large twisted
bilayer structures, when these are derived from predicted densities. We demonstrate that the choice of descriptor determines the distribution of residual density errors, which in turn affects the downstream electronic properties. We apply our models to twisted
bilayer graphene, hexagonal boron nitride, and transition metal dichalcogenides, focusing on the model's capacity to predict complex phenomena, including flat band formation, bandwidth narrowing, domain-wall electric fields, and
spin-orbit coupling effects. Beyond moiré materials, this approach provides a general methodology for electronic structure prediction in large-scale systems with substantial long-range phenomena related to non-local
geometric information.
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Materials Science · Cross-listed from cond-mat.mes-hall
Refined DFT recipe and renormalisation of band-edge parameters for electrons in monolayer MoS$_2$ informed by the measured spin-orbit splitting
Igor Rozhansky, Michele Masseroni, Ricardo Pisoni et al. (+6 more)
Conduction band-edge
spin-orbit splitting (SOS) in monolayer transition metal dichalcogenides determines a competition between bright and dark
excitons and sets conditions for spintronics applications of these
semiconductors. Here, we report the SOS measurement for electrons in monolayer MoS$_2$, found from the threshold density, $n_*$, for the upper
spin-orbit-split band population, which exceeds by an order of magnitude the values expected from the conventional density functional theory (DFT). Theoretically, half of the observed value can be attributed to the exchange enhancement of SOS in a finite-density electron gas, but explaining the rest requires refining the DFT approach. As the conduction band SOS in MoS$_2$ is set by a delicate balance between the contribution of sulphur $p_x$ and $p_y$ orbitals and $d_{z^2}-d_{xz}$ and $d_{z^2}-d_{yz}$ mixing in molybdenum, we use a DFT+U+V framework for fine-tuning the orbital composition of the relevant band-edge states. An optimised choice of Hubbard U/V parameters produces close agreement with the experimentally observed conduction band SOS in MoS$_2$, simultaneously resulting in the valence-band SOS and the quasi-particle band gap which are closer to their values established in the earlier-published experiments.
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All authors Igor Rozhansky, Michele Masseroni, Ricardo Pisoni, Suad Alshammari, Xue Li, Thomas Ihn, Klaus Ensslin, James McHugh, Vladimir Fal'ko
Materials Science
Multiple Layer-Selective Polar Charge Density Waves in ${\rm{EuTe}}_{4}$
Wen-Han Dong, Wenhui Duan, Yong Xu et al. (+1 more)
${\rm{EuTe}}_{4}$ is a polar charge density wave (CDW) material, with
giant thermal hysteresis and non-volatile state switching under electric and optical fields, attracting great
attention in recent years. However, the in-depth understanding of these anomalous phenomena remains elusive. Herein, via first-principles calculations, we reveal that the polar CDW state in ${\rm{EuTe}}_{4}$ hosts a novel layer-selective nature, wherein multiple energetically close CDW configurations coexist and exhibit low interconversion energy barriers. Monte Carlo simulations indicate that the
giant thermal hysteresis in ${\rm{EuTe}}_{4}$ originates from a phase transition mainly driven by the change of configurational
entropy, around which the material hosts a metastable CDW state characterized by diverse local polar configurations breaking the out-of-plane translational
symmetry. The configurational composition of this metastable CDW state can be effectively controlled by electric and optical fields, thereby enabling non-volatile state switching. Our theoretical findings align well with recent experimental observations in ${\rm{EuTe}}_{4}$ and pave the way for exploring the emerging phenomena and applications of polar CDW in multilayered systems.
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All authors Wen-Han Dong, Wenhui Duan, Yong Xu, Peizhe Tang
Materials Science
Exciton fine structure in CdSe nanoplatelets using a quasi-2D screened configuration-interaction framework
Sumanti Patra and Gabriel Bester
We compute
exciton binding energies and fine-structure splittings in CdSe nanoplatelets with two zincblende geometries and one wurtzite geometry, finding that the wurtzite structure exhibits the largest bright-bright splitting due to its intrinsic in-plane anisotropy, while the zincblende structures show smaller but finite splittings arising from atomistic
symmetry breaking at edges and corners. These results are obtained using a theoretical framework that we developed, which combines DFT single-particle states with screened configuration interaction, a quasi-2D dielectric screening model, and an efficient Coulomb-cutoff scheme that eliminates periodic-image interactions and enables accurate Coulomb and exchange integrals at low computational cost. This methodology provides a transferable and practical route for studying
excitons in CdSe nanoplatelets and other quasi-two-dimensional nanomaterials.
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Materials Science · Cross-listed from physics.ins-det
A 4D-STEM Tomographic Framework Assisted by Object Tracking for Nanoparticle Structure Determination
Saleh Gholam, Arno Annys, Irina Skvortsova et al. (+6 more)
Three-dimensional electron diffraction (3D ED) has emerged as a powerful method for solving the structures of sub-micron-sized particles down to nanoparticles. However, it faces technical challenges when applied to beam-sensitive samples or agglomerated nanoparticles. This study presents a novel approach that combines 4D-STEM
tomography with object tracking and
segmentation algorithms to overcome these limitations and achieve single-crystalline 3D ED
datasets from nanopowder samples. The method and data quality are assessed on brookite TiO2 nanorods and beam-sensitive CsPbBr3 nanoparticles. To finely sample the reciprocal-space, the data acquisition was automated to acquire hundreds of 4D-STEM scans at fine tilt steps using a slightly convergent beam (0.6 to 1 mrad). Compared to conventional 3D ED methodologies, the proposed method provides enhanced signal-to-noise ratio, low illumination time for reducing beam damage, and the ability to analyze multiple particles from a single tomographic
dataset. The procedure is optimized to be feasible using commercially available desktops and detectors. This extends the method applicability to systems and samples that were very challenging for conventional 3D ED methods, by eliminating several technical challenges for the data acquisition.
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All authors Saleh Gholam, Arno Annys, Irina Skvortsova, Erica Cordero Oyonarte, Amirhossein Hajizadeh, Philippe Boullay, Johan Hofkens, Johan Verbeeck, Joke Hadermann
Materials Science
Giant thermopower changes related to the resistivity maximum and colossal magnetoresistance in EuCd2P2
Judith Grafenhorst, Sarah Krebber, Kristin Kliemt et al. (+3 more)
We present the thermopower of EuCd2P2, a material which exhibits a large resistivity peak with significant
magnetic field dependence in the temperature range of 10-25 K. In the same region we observe a highly unusual behavior of the thermopower with two sign changes and
giant extrema. The overall variation of the thermopower exceeds 4 000 muV/K and takes place in an extremely narrow temperature region of less than 5 K. The anomaly is suppressed completely in a small
magnetic field of 0.5 T. We discuss this observation using a simple drift-
diffusion picture and taking into account that the temperature gradient inducing the thermopower voltage is accompanied by a gradient of the electrical resistivity. Our simple estimation yields the correct magnitude, shape, and field dependence of the thermopower anomaly observed in EuCd2P2. These results open a new route to
giant thermopower values via gradients of electronic properties.
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All authors Judith Grafenhorst, Sarah Krebber, Kristin Kliemt, Cornelius Krellner, Elena Hassinger, Ulrike Stockert
Materials Science
MoireStudio: A Universal Twisted Electronic Structure Calculation Package
Junxi Yu, Yichen Liu and Cheng-Cheng Liu
Twistronics is an emerging and captivating field in condensed matter physics and material science. However, accurately and efficiently calculating the electronic structures of twisted systems remains a significant challenge. To address this, we have developed MoireStudio, a universal Python-based computational package for twisted electronic structures. Its functionalities include commensurate structure search, structure generation, parameterization, and construction for tight-binding models and continuum models, and the precise incorporation of full relaxation effects. The package is applicable to arbitrary combinations of two-dimensional materials, including rectangular
lattices and
heterostructures. User-friendly and easy to use, MoireStudio supports parallel large-scale computations, provides visualization capabilities, and offers interfaces with third-party software. It is poised to become a convenient and powerful tool for researchers in twistronics fields.
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Materials Science
How Geometry Tames Disorder in Lattice Fracture
Matthaios Chouzouris, Leo de Waal, Antoine Sanner et al. (+3 more)
We investigate the fracture behavior of pre-cracked triangular beam-
lattices whose elements have failure stresses drawn from a Weibull distribution. Through a statistical analysis and numerical simulations, we identify and verify the existence of three distinct failure regimes: (i) disorder is effectively suppressed, (ii) disorder manifests locally near the crack tip, modifying the crack morphology, and (iii) disorder manifests globally, leading to initially diffuse failure. Our model naturally reveals the key parameters governing this behavior: the Weibull modulus, quantifying the spread in failure thresholds, and a
geometric quantity termed the Slenderness Ratio. We also reproduce the disorder-induced toughening reported in previous experimental and numerical studies, further demonstrating that its manifestation depends non-monotonically on disorder. Crucially, our results indicate that this toughening cannot be simply connected to the amount of damage in the
lattice, challenging interpretations that attribute increased fracture energy solely to enhanced crack tortuosity or diffuse failure. Overall, our results establish geometry as a powerful control parameter for regulating how disorder is expressed during fracture in beam-
lattices, with broader implications for the disorder-induced toughening in engineered materials.
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All authors Matthaios Chouzouris, Leo de Waal, Antoine Sanner, Alessandra Lingua, David S. Kammer, Marcelo A. Dias
Materials Science
Pressure dependent topological, superconducting, optoelectronic and thermophysical properties of Ta2Se chalcogenide: Theoretical insights
Tauhidur Rahman, Jubair Hossan Abir, Sourav Kumar Sutradhar et al. (+4 more)
Tetragonal Ta2Se is a layered, Ta-rich chalcogenide that departs from conventional MX2 transition-metal dichalcogenides by hosting dense Ta-Ta networks capped by Se square-net layers. Here, we present a unified first-principles investigation of hydrostatic-pressure tuning in Ta2Se from 0 to 10 GPa, connecting the structural response, mechanical stability, thermophysical indicators, bonding
evolution, electronic and optical behavior,
lattice dynamics and superconductivity within a single framework. The derived thermophysical descriptors corroborate a pressure-stiffened
lattice: density increases, Debye temperature rises, melting temperature is elevated and minimum thermal conductivity increases, whereas the Grüneisen parameter remains within a narrow window, suggesting no anomalous anharmonic softening. Bond population metrics and electron-density-difference analysis revealed a mixed metallic-covalent bonding picture dominated by a robust Ta-Ta metallic backbone, accompanied by pressure-strengthened Ta-Se hybridization. Electronic-structure calculations show persistent
metallicity under compression; pressure broadens bands, reduces density of states at the
Fermi level, reshapes the
Fermi surface and points to a possible Lifshitz-type reconstruction without
symmetry breaking. The optical response remained metallic with Drude-like low-energy behavior and pressure-tunable spectral features. The
phonon dispersions exhibit no imaginary modes, confirming dynamical stability. Electron-
phonon coupling calculations classify Ta2Se as a weak-coupling,
phonon-mediated
superconductor with Tc around 3.9 K, consistent with available experiments and establish pressure as a practical control knob for stability and superconductivity-relevant descriptors in this metal-rich layered platform.
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All authors Tauhidur Rahman, Jubair Hossan Abir, Sourav Kumar Sutradhar, Sraboni Saha Moly, Mst. Maskura Khatun, Md. Asif Afzal, Saleh Hasan Naqib
Materials Science
Microstructural origin of the simultaneous enhancements in strength and ductility of a nitrogen-doped high-entropy alloy
Xiaoxiang Wu, Zhujun Sun, Wenqi Guo et al. (+9 more)
As one of the most abundant interstitial elements, nitrogen (N) is effective in improving yield strength of metallic materials, due to interstitial solid solution strengthening. Doping N can substantially enhance the yield strength but often leads to a decreased ductility, revealing a strength-ductility trade-off phenomenon. Here, we simultaneously enhance the strength and ductility in a non-equiatomic CrMnFeCoNi high-
entropy alloy via N alloying and unravel the underlying microscopic mechanisms. The N-doped
alloy (1 at.% N) shows an excellent combination of higher yield strength (104% increase) and larger ductility (38% increase), with a two-stage strain hardening behavior, compared to the N-free
alloy. Detailed transmission electron microscopy (TEM) analysis reveals that N-doping introduces short-range order (SRO) domains within the microstructure, leads to pronounced planar slip, and promotes the formation of nano-spaced (6-15 nm) stacking faults and deformation twins. Continuous generation and interaction of the fine-spaced SFs act as a strong barrier for dislocation movement and provide ample room for dislocation storage. The interaction of SRO with dislocations and the
evolution of SFs ascribe to the first strain hardening stage, and the disordering of the SRO along with the activation of deformation twins are attributed to the second strain hardening stage. Our work shows that N-doping is effective in simultaneously improving the strength-ductility synergy and provides novel insights into
alloy design with slightly elevating the SFE, and manipulating the ordered structure within the HEA.
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All authors Xiaoxiang Wu, Zhujun Sun, Wenqi Guo, Chang Liu, Yong-Qiang Yan, Yan-Ning Zhang, Yuji Ikeda, Fritz Körmann, Jörg Neugebauer, Zhiming Li, Baptiste Gault, Ge Wu
Materials Science
High Photovoltaic Efficiency in Bulk-Stacked One-Dimensional GeSe$_{2}$ van der Waals Crystal
Seoung-Hun Kang, Youngjae Kim, Bo Gyu Jang et al. (+1 more)
Germanium diselenide (GeSe$_{2}$) has recently attracted substantial interest as a rare example of one-dimensional (1D) van der Waals material. Here, we investigate the photovoltaic potential of bulk-stacked GeSe$_{2}$ chains using first-principles calculations within the $GW0$ approximation and the Bethe-Salpeter equation (BSE) to capture quasiparticle and excitonic effects. The bulk GeSe$_{2}$ exhibits indirect GW band gaps of 1.92 eV (type-I) and 1.08 eV (type-II). Optical calculations show markedly stronger visible-light absorption in type-II, yielding a spectroscopically limited maximum efficiency (SLME) of ~25.6% at a 0.5 $\mu$m thickness.
Phonon and room-temperature ab initio molecular dynamics analyses indicate that type-II is dynamically stable, whereas type-I shows imaginary
phonon modes, suggesting a propensity for structural distortion. These results identify type-II GeSe2 as a promising stable absorber for thin-film photovoltaics with enhanced flexibility compared to typical 2D vdW systems.
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All authors Seoung-Hun Kang, Youngjae Kim, Bo Gyu Jang, Sejoong Kim
Materials Science · Cross-listed from cond-mat.mes-hall
Direct Visualization of Room-temperature Stair-stepped Quantum Spin Hall States in Bi4Br4
Zhiqiang Hu, Yuqi Zhang, Yuyang Wang et al. (+7 more)
Topological
insulators host exotic
quantum phenomena such as the
quantum spin Hall (QSH) effect, which enables dissipationless one-dimensional edge conduction. Realizing such states at room temperature and on a macroscopic scale is essential for energy-efficient electronics and
quantum technologies, yet remains a fundamental challenge due to material limitations. Here, using microwave impedance microscopy, we directly visualize robust QSH states persisting up to 300 K in {\alpha}-Bi4Br4 nanowires. This stability and scalability are enabled by a stair stepped stacking configuration, a multilayer geometry in which QSH edge states from individual layers remain spatially decoupled. This configuration circumvents the stringent
alignment and layer number constraints of previous proposals, allowing robust stair-stepped QSH (SS-QSH) conduction in structures several micrometers long and hundreds of nanometers high.
Magnetic field and temperature dependent measurements confirm their intrinsic topological nature. Crucially, the SS-QSH and bulk signals scale with nanowire height, verifying the stair stepped origin. Our results are also successfully reproduced by finite-element analysis simulations. This work establishes {\alpha} Bi4Br4 as a practical platform for high temperature topological electronics and demonstrates a generalizable stacking strategy for designing scalable QSH systems.
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All authors Zhiqiang Hu, Yuqi Zhang, Yuyang Wang, Kebin Xiao, Xiang Li, Zhiwei Wang, Huaixin Yang, Yugui Yao, Qi-Kun Xue, Wei Li
Materials Science
Cavity control of multiferroic order in single-layer NiI$_2$
Chongxiao Fan, Emil Viñas Boström, Xinle Cheng et al. (+5 more)
Controlling materials through their interactions with electromagnetic
vacuum fluctuations is an emergent frontier in material engineering. Although recent experiments have demonstrated dark cavity effects for electronic material phases, like superconductivity, ferroelectricity and charge density waves, a smoking gun experiment for
magnetic systems is lacking. Largely, this comes from the focus on phase transitions, where a large critical light-matter coupling is needed to observe cavity modifications. Here, we propose spiral magnets, where even a small cavity-mediated change in
magnetic interactions is reflected in a change of the spiral wavelength, as a promising platform to observe cavity effects. We focus on the single-layer multiferroic NiI$_2$, interacting with electric field fluctuations from surface
phonon polaritons of the paraelectric substrate SrTiO$_3$. With decreasing substrate-material distance, the ratio of nearest and third nearest neighbor exchange interactions reduces, leading to an increase of the spiral wavelength and an eventual transition into a
ferromagnetic state. Our work identifies a realistic platform to observe cavity
vacuum renormalization effects in
magnetic systems.
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All authors Chongxiao Fan, Emil Viñas Boström, Xinle Cheng, Lukas Grunwald, Zhuquan Zhang, Dante M. Kennes, Dmitri N. Basov, Angel Rubio
Materials Science · Cross-listed from physics.optics
Background-free Tracking of Ultrafast Hole and Electron Dynamics with XUV Transient Grating Spectroscopy
Vincent Eggers, Rafael Quintero-Bermudez, Kevin Gulu Xiong et al. (+1 more)
Extreme ultraviolet (XUV) transient absorption (TA) and transient reflectivity (TR) spectroscopies enable element-specific insights into attosecond-timescale processes in solids. XUV transient grating spectroscopy (TGS) is an emerging tool that combines the advantages of both absorption and reflectivity while offering intrinsically background-free detection. Here, we implement XUV-TGS by generating a transient grating in germanium solid using two few-cycle near-infrared pulses and probing it with an attosecond XUV pulse, produced via tabletop high-harmonic generation. The spectrally resolved, diffracted XUV pulses directly visualize the separate ultrashort decay times of both photoexcited electrons and holes, without the need for iterative deconvolution. By combining XUV-TA and -TG spectroscopy, we extract the
evolution of the complex refractive index, ñ, without the need for Kramers-Kronig reconstruction, as required in XUV-TR, allowing us to extract the roots of the induced optical response. We find reflectivity changes of up to 34% via the real part of ñ, whereas changes in the imaginary part only result in a variation in reflectivity of around 0.5%.
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All authors Vincent Eggers, Rafael Quintero-Bermudez, Kevin Gulu Xiong, Stephen R. Leone