Materials Science
Towards predictive atomistic simulations of SiC crystal growth
Alexander Reichmann, Zahra Rajabzadeh, Sebastian Hofer et al. (+2 more)
Simulations of SiC
crystal growth using molecular dynamics (MD) have become popular in recent years. They, however, simulate very fast deposition rates, to reduce computational costs. Therefore, they are more akin to surface sputtering, leading to abnormal growth effects, including thick amorphous layers and large defect densities. A recently developed method, called the minimum energy atomic deposition (MEAD), tries to overcome this problem by depositing the atoms directly at the minimum energy positions, increasing the time scale. We apply the MEAD method to simulate SiC
crystal growth on stepped C-terminated 4H substrates with 4{\deg} and 8{\deg} off-cut angle. We explore relevant calculations settings, such as amount of equilibration steps between depositions and influence of simulation
cell sizes and bench mark different interatomic potentials. The carefully calibrated methodology is able to replicate the stable step-flow growth, which was so far not possible using conventional MD simulations. Furthermore, the simulated
crystals are evaluated in terms of their dislocations, surface roughness and atom mobility. Our methodology paves the way for future high fidelity investigations of surface phenomena in
crystal growth.
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All authors Alexander Reichmann, Zahra Rajabzadeh, Sebastian Hofer, René Hammer, Lorenz Romaner
Materials Science · Cross-listed from cs.LG
Symbolic regression for defect interactions in 2D materials
Mikhail Lazarev and Andrey Ustyuzhanin
Machine learning models have become firmly established across all scientific fields. Extracting features from data and making inferences based on them with neural network models often yields high accuracy; however, this approach has several drawbacks. Symbolic regression is a powerful technique for discovering analytical equations that describe data, providing interpretable and generalizable models capable of predicting unseen data. Symbolic regression methods have gained new momentum with the advancement of neural network technologies and offer several advantages, the main one being the interpretability of results. In this work, we examined the application of the deep symbolic regression
algorithm SEGVAE to determine the properties of two-dimensional materials with defects. Comparing the results with state-of-the-art graph neural network-based methods shows comparable or, in some cases, even identical outcomes. We also discuss the applicability of this class of methods in natural sciences.
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Materials Science
Bias, length, or coupling? What controls the quantum efficiency of electroluminescent single-polymers
Facundo Tarasi, Esteban D. Gadea, Tchavdar Todorov et al. (+1 more)
Since the first evidence of luminescence of organic
polymers in STM junctions, efforts have been invested in elucidating how to leverage the voltage, anchoring chemistry, and molecular structure to optimize emission power and efficiency. Understanding the fundamentals underlying current-driven molecular emission is important not only for OLED engineering, but also to control luminescence at the atomic scale toward the mastering of single or localized
photon sources. However, the difficulty in isolating the separate roles of the variables at play in molecular junction experiments, has precluded a general comprehension of their distinctive effects on the emitted power and the
quantum yield. In the present report, we use time-dependent electronic structure simulations based on
quantum electrodynamics to disentangle the incidence of bias, electronic coupling and molecular length on device performance, with polyphenylene-vinylene as a case study. A careful validation demonstrates that our approach can achieve quantitative agreement with available experimental data. Through its application we identify the applied bias as the main factor determining emission power. The
quantum efficiency, however, is influenced only minimally by bias and electronic coupling, and is instead dominated by
polymer length, on which it depends exponentially. Thus, using longer
polymer chains emerges as the primary strategy for achieving higher efficiencies. Our results thereby provide key prescriptions for designing single-molecule electroluminescent platforms.
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All authors Facundo Tarasi, Esteban D. Gadea, Tchavdar Todorov, Damian A. Scherlis
Materials Science · Cross-listed from cond-mat.dis-nn
Statistical mechanics for organic mixed conductors: phase transitions in a lattice gas
Lukas M. Bongartz
Organic mixed conductors (OMCs) represent a promising class of materials for applications in bioelectronics, physical computing, and thermoelectrics. Rather unparalleled, OMCs feature dynamics spanning multiple length and time scales, involving an intricate coupling between electronic, ionic, and mass transport. These characteristics set them notably apart from traditional
semiconductors and hinder the description by conventional
semiconductor theory. In this work, we approach the charge carrier modulation of OMCs using statistical mechanics. We discuss OMCs from a thermodynamic perspective and contrast them with established
semiconductor materials, highlighting key differences in their collective charge carrier dynamics. This motivates our description of OMCs as a
lattice gas, which we analyze within the grand canonical ensemble. The model exhibits a first-order phase transition analogous to a classical vapor$\unicode{x2013}$
liquid transition, governed by temperature and chemical potential. In doing so, it captures the formation of distinct low- and high-density carrier phases, consistent with recently reported experimental observations. It also illustrates how metastability near the phase boundary can give rise to history-dependent characteristics in device operation, a similarly well-reported effect in OMC transistors. This work is intended as a simple motivation for studying OMCs through the lens of statistical mechanics, offering a more natural description than traditional
semiconductor models developed for materials of fundamentally distinct character.
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Materials Science
Inter-defect interactions, oxygen-vacancy distribution, and oxidation in acceptor-doped ABO3 perovskites
L.P. Putilov, M.Z. Uritsky and V.I. Tsidilkovski
The effects of inter-defect interaction and
impurity disorder on defect thermodynamics, local ion coordination, and oxidation in acceptor-doped wide-gap ABO3 perovskites are explored using the developed statistical theory and Monte Carlo simulations. The results demonstrate that under realistic energy parameters the interaction between oxygen vacancies and
impurities generally has a greater impact on the studied properties than inter-vacancy correlations. The influence of inter-vacancy interaction significantly depends on dopant content x: inter-site vacancy repulsion becomes noticeable at sufficiently high x, whereas on-site correlations can be pronounced within a narrow doping range at moderate x values. It is found that a non-uniform
impurity allocation, which can result from a sample preparation procedure, considerably affects oxygen-vacancy distribution, and has a weaker effect on short-range order and oxidation. It is also shown that inter-defect interaction reduces the hole concentration, increases the oxidation enthalpy, and can result in their non-trivial dependence on x. The obtained results agree with experimental data on local ion coordination and help to explain the behavior of hole conductivity in the considered perovskites. The findings of this study contribute to understanding the fundamental properties of acceptor-doped
oxides, facilitating the development of new materials for clean energy applications.
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Materials Science
Applications of silicon carbide as window materials in atomic cells and atomic devices
Z.-P. Xie, C.-P. Hao and D. Sheng
Atomic
cells made by anodically bonding silicon and borosilicate glasses are widely used in atomic devices. One inherent problem in these
cells is that the silicon material blocks beams with wavelengths shorter than 1000 nm, which limits available optical accesses when alkali metal atoms are involved. In this work, we investigate the possibility of the silicon carbide material as an alternative of silicon materials in fabricating anodically bonded
cells. We demonstrate that the optical, thermal and mechanical properties of silicon carbide help to improve the performance of atomic devices in certain applications.
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Materials Science
Kinetic energy functional constructed from exact gradient expansion of second order in uniform gas limit
Abhishek Bhattacharjee, Hemanadhan Myneni, Manoj K. Harbola et al. (+1 more)
Orbital-Free Density Functional Theory (OFDFT) has re-emerged as a viable alternative to Kohn-Sham DFT, driven by recent advances in kinetic energy density functionals (KEDFs). Nonlocal (NL) KEDFs have significantly extended OFDFT's applicability, particularly for bulk solids, but their high computational cost and dependence of system-specific parameters limit their universality. In this work, we propose a semilocal KEDF at the Generalized Gradient Approximation (GGA) level that achieves accuracy comparable to state-of-the-art NL and meta-GGA functionals, while remaining entirely parameter-free. Our construction revives the Thomas-
Fermi-von Weizsacker (TFvW) framework by modulating the relative contributions of TF and vW terms through physically motivated constraints and preserving the exact second-order gradient expansion. Despite its simple form, the proposed functional (KGE2) performs remarkably well across both extended systems (metals and
semiconductors) and finite systems (clusters), without any need for parameter tuning. These results mark a step toward a transferable, computationally efficient, and general-purpose KEDF suitable for large-scale OFDFT simulations.
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All authors Abhishek Bhattacharjee, Hemanadhan Myneni, Manoj K. Harbola, Prasanjit Samal
Materials Science · Cross-listed from cond-mat.supr-con
Cuprates, Pnictides and Sulfosalts: Lessons in Functional Materials
N. Barišić and D. K. Sunko
Murunskite K$_2$Cu$_3$FeS$_4$ is a representative sulfosalt, isostructural to the pnictides, but with electronic properties more similar to the insulating parent compounds of the cuprates. We use it as a bridge to compare the chemical and physical roles of metal and ligand orbitals in cuprates and pnictides. In cuprates, ionicity, covalency, and
metallicity are tightly interwoven to give rise to high-temperature superconductivity (SC). Their most remarkable property is the interaction of an ionically localized hole on the copper (Cu) with a
Fermi liquid (FL) on the oxygens (O), which is critically important for understanding all key properties of these materials. The localization is due to strong correlations on the Cu $3d$ orbital. We describe a scenario in which the localized hole gives rise both to SC by Cooper scattering of O holes, and to
Fermi arcs, as observed in cuprate spectroscopy, the latter by a purely kinematic projection of the static local disorder, without invoking any residual interactions between the mobile O FL carriers. In the pnictides, the orbitals responsible for binding and metallic conduction appear to be separate. The Fe $3d$ $e_{g}$ orbitals hybridized with the ligands set the
lattice spacing. The $3d$ $t_{2g}$ orbitals overlap directly between the Fe atoms, resulting in several electronic bands appearing at the
Fermi level. The ensuing
Fermi liquid exhibits both charge and
magnetic correlations. We argue that a similar SC scenario as in the cuprates is plausible in the pnictides, except that a light FL scatters on a slow nearly-
antiferromagnetic (AF) one, rather than on localized holes as in the cuprates.
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Materials Science · Cross-listed from cond-mat.mes-hall
Magneto-Moiré Excitons in Twisted Bilayer CrSBr
Qiuyang Li, Anton Shubnic, Nishkarsh Agarwal et al. (+15 more)
Moiré superlattices in van der Waals materials have revolutionized the study of electronic and excitonic systems by creating periodic electrostatic potentials. Extending this concept to
magnetic materials promises new pathways in merging spintronics with photonics. While moiré magnetism has been revealed with near-field probes and nonlinear optical techniques, the coupling of these
magnetic textures to optical excitations - magneto-moiré
excitons - remains unexplored. Here, we report the observation of magneto-moiré
excitons in twisted
bilayer CrSBr, correlated with moiré
spin textures that emerge below a critical twist angle of ~2{\deg}. The nanoscale moiré
spin texture imprints distinct signatures onto the optical spectrum, shifting the
exciton energy via a periodic
magnetic exchange field. First-principles calculations corroborate that these signatures arise from one-dimensional
spin textures governed by the balance of exchange interactions and domain wall energy. Our results demonstrate that moiré magnetism can be used to engineer nanoscale excitonic energy landscapes, providing a new platform for magneto-optical sensing,
quantum transduction, and control of non-collinear magnetism and
topology through light.
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All authors Qiuyang Li, Anton Shubnic, Nishkarsh Agarwal, Adam Alfrey, Wenhao Liu, Zixin Zhai, Igor Lobanov, Valery Uzdin, Senlei Li, Yujie Yang, Wyatt Alpers, Kai Sun, Liuyan Zhao, Chunhui Rita Du, Bing Lv, Robert Hovden, Ivan A. Shelykh, Hui Deng
Materials Science · Cross-listed from cond-mat.soft
Viscoelastic Material Properties of Gelatin with Varying Water to Collagen mass Ratios
Joseph E. Bonavia
Gelatin is often used as an analog for studying soft and biological materials in order to understand the mechanics of behavior of biological tissue in events like traumatic
brain injuries. The material properties of gelatin change with the ratio of water to gelatin powder used to make a given sample. Characterizing the relationship between this ratio and the material properties of gelatin is crucial to enable its use in mechanics experiments. In this work, compression tests were performed on a texture analyzer on samples which ranged from a 2:1 to 20:1 ratio of water to gelatin powder. In this range, instantaneous stiffnesses were well fit via power law in this ratio and decreased from 277 +/- 30 kPa to 4.34 +/- 0.64 kPa. The dominant (longest) timescales of the samples were well fit via a sigmoid function in this ratio and increased from 29.8 +/- 1.0 s to 621 +/- 92 s. The resulting ratio-property relationships offer a functional way to design gelatin samples for use in mechanics experiments.
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Materials Science · Cross-listed from cond-mat.mes-hall
Electronic states at twist stacking faults in rhombohedral graphite
Xiaoqian Liu, Yifei Guan and Oleg V. Yazyev
Flat bands in graphitic materials emerged as a platform for realizing tunable correlated physics. As a nodal-line semimetal, rhombohedral graphite features flat drumhead surface states in the vicinity of the Dirac points, which carry a nontrivial topological charge. We present a comprehensive study on rhombohedral graphite with twist stacking faults. Using both the continuum models and the realistic tight-binding models, we show that the twist angle between the
graphene layers can tune the interface states at such stacking faults. The
evolution of interface states originates from the interplay between the moiré periodicity and Zak phase
topology, predicting the occurrence of nearly flat bands throughout the moiré Brillouin zone. We further investigate the disorder-induced layer polarization and tunable Chern number for flat band, and characterize the relationship between the disorder strength and Chern number in twisted rhombohedral graphite.
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Materials Science
Iterative learning scheme for crystal structure prediction with anharmonic lattice dynamics
Hao Gao, Yue-Wen Fang and Ion Errea
First-principles based
crystal structure prediction (CSP) methods have revealed an essential tool for the discovery of new materials. However, in solids close to displacive phase transitions, which are common in ferroelectrics, thermoelectrics, charge-density wave systems, or superconducting hydrides, the ionic contribution to the free energy and
lattice anharmonicity become essential, limiting the capacity of CSP techniques to determine the thermodynamical stability of competing phases. While variational methods like the
stochastic self-consistent harmonic approximation (SSCHA) accurately account for anharmonic
lattice dynamics ab initio, their high computational cost makes them impractical for CSP. Machine-learning interatomic potentials offer accelerated sampling of the energy landscape compared to purely first-principles approaches, but their reliance on extensive training data and limited generalization restricts practical applications. Here, we propose an iterative learning framework combining evolutionary
algorithms, atomic foundation models, and SSCHA to enable CSP with anharmonic
lattice dynamics. Foundation models enable robust relaxations of random structures, drastically reducing required training data. Applied to the highly anharmonic H$_3$S system, our framework achieves good agreement with the
benchmarks based on density functional theory, accurately predicting phase stability and vibrational properties from 50 to 200 GPa. Importantly, we find that the statistical averaging in the SSCHA reduces the error in the free energy evaluation, avoiding the need for extremely high accuracy of machine-learning potentials. This approach bridges the gap between data efficiency and predictive power, establishing a practical pathway for CSP with anharmonic
lattice dynamics.
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Materials Science
Surface Exciton Polaritons and Near-Zero Permittivity Surface Waves Supported by Artificial Organic Hyperbolic Metamaterials
José N. Gama, Diogo Cunha, Carla Estévez-Varela et al. (+11 more)
Hyperbolic metamaterials enable extreme light confinement and control of photonic states, but their realization has been restricted to inorganic architectures. Here, a fully organic route to fabricate artificial
hyperbolic metamaterials based on multilayered thin films of J-aggregate carbocyanine dyes alternated with polyelectrolytes is introduced. These structures exhibit strong optical anisotropy and experimentally support
hyperbolic surface
exciton polaritons and, for selected dyes, additional surface waves in near-zero permittivity regimes. Spectroscopic ellipsometry confirms a uniaxial dielectric tensor with negative in-plane and positive out-of-plane components, close to the absorption peaks of the constituent J-aggregates. This anisotropy is preserved across individual layers, demonstrating the robustness of the layer-by-layer approach and enabling the coupling of surface
exciton polaritons and near-zero permittivity modes even in films only a few nanometres thick. Transfer-
matrix simulations based on the obtained dielectric tensor reproduce the coupling conditions for all thicknesses, validating the optical model. Structural characterization reveals the link between optical anisotropy and supramolecular order, with preferential in-plane molecular orientation and the
evolution from discrete nanostructures to continuous films as deposition progresses. These organic
hyperbolic metamaterial architectures, associated with narrow excitonic resonances from J-aggregates, offer a unique platform for tailoring emission, energy transport, and exploring polariton dynamics at the nanoscale.
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All authors José N. Gama, Diogo Cunha, Carla Estévez-Varela, Marina García-Pardo, Pablo Pedreira, Adelaide Miranda, M. Carmen López-González, Pieter A.A. De Beule, Eduardo Solano, Rosalia Serna, Mikhail Vasilevskiy, Martin Lopez-Garcia, Isabel Pastoriza-Santos, Sara Núñez-Sánchez
Materials Science · Cross-listed from cond-mat.mes-hall
Intercalant-induced Kekule ordering and gap opening in quasi-free-standing graphene
Huu Thoai Ngo, Zamin Mamiyev, Niklas Witt et al. (+2 more)
We present a comprehensive investigation of the structural and electronic properties of Sn intercalated buffer layers on SiC(0001) using low-temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS), spot-profile analysis low-energy electron diffraction (SPA-LEED), and density functional theory (DFT) calculations. Sn intercalation effectively decouples the buffer layer, yielding quasi-free-standing monolayer
graphene (QFMLG) while introducing local
lattice distortions. Bias-dependent STM imaging revealed the coexistence of conventional and Kekule-ordered
graphene domains, governed by the underlying Sn(1x1) reconstruction at the SiC interface. The measured STS spectra exhibit good agreement with DFT results. However, achieving homogeneous Sn(1x1) domains remains challenging, apparently, due to strain within the Sn monolayer, which drives the emergence of Kekule distortions and the associated electronic band-gap opening omogeneously in
graphene. These findings highlight the crucial role of intercalant homogeneity and strain in tuning
graphene`s structural and electronic properties.
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All authors Huu Thoai Ngo, Zamin Mamiyev, Niklas Witt, Tim Wehling, Christoph Tegenkamp
Materials Science · Cross-listed from cond-mat.supr-con
Distinct Suppression Mechanisms of Superconductivity by Magnetic Domains and Spin Fluctuations in EuFe2(As1-xPx)2 superconductors
Mengju Yuan, Nan Zhou, Ruixia Ti et al. (+10 more)
Using ac composite magnetoelectric technique, we map the phase diagrams of EuFe(As1-xPx)2 to resolve the interplay between superconductivity and ferromagnetism. For samples with Tc<TFM, the transition to a
ferromagnetic multi-domain state suppresses Hc2 through the breakdown of Jaccarino-Peter compensation and enhanced
magnetic scattering from inter-domain disorder, while Hirr is reduced due to
vortex-antivortex pair nucleation at domain walls disrupting the
vortex lattice. Conversely, for samples with Tc>TFM, strong short-range
spin correlations and phase boundaries within a multiphase coexistence regime near the triple point act as potent pair-breaking centers, leading to pronounced Hc2 suppression.
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All authors Mengju Yuan, Nan Zhou, Ruixia Ti, Long Zhang, Chenyang Zhang, Tian He, Deliu Ou, Jingchun Gao, Mingquan He, Aifeng Wang, Jun-Yi Ge, Yue Sun, Yisheng Chai
Materials Science
Co$_2$MnZ (Z = Al, Si, Ga, Ge, Sn) Heusler alloys as candidate materials for spintronic and microelectronic applications: Electronic structure, transport, and magnetism
Vyacheslav V. Marchenkov, Alena A. Semiannikova, Evgenii D. Chernov et al. (+4 more)
Magnetic and electronic transport properties of Co$_2$MnZ (Z = Al, Ga, Ge, Si, Sn) Heusler
alloys were experimentally investigated. Electrical resistivity, in the temperature range from 4.2 to 300 K, as well as field dependences of the
Hall effect and magnetization at T = 4.2 K in
magnetic fields up to 100 kOe and 70 kOe, respectively, were measured. Experimental data are in good agreement with the results of the theoretical DFT calculations of the electronic structure and
magnetic moments. In the band structure of Co$_2$MnSi, half-
metallicity is formed with the full
spin polarization and the half-metallic gap of about 0.6 eV. In Co$_2$MnZ (Z = Al, Ge, Sn), it is shifted from the
Fermi energy by the hole pockets at the point $\Gamma$, preventing thereby the formation of the half-metallic state. In a peculiar case of Co$_2$MnGa, the antisite defects are expected to determine structural and electronic properties. For the Co$_2$MnAl and Co$_2$MnGa topological semimetals, Weyl topological points are found at the
Fermi energy; however, for Z = Si, Ge, Si, these features are located deeper within to the valence band. The results show that Co$_2$MnGe and Co$_2$MnSn are usual ferromagnets, Co$_2$MnAl and Co$_2$MnGa
alloys are topological semimetals that can find application in microelectronics, while Co$_2$MnSi is a half-metallic ferromagnet that is in high demand in spintronics.
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All authors Vyacheslav V. Marchenkov, Alena A. Semiannikova, Evgenii D. Chernov, Alexey V. Lukoyanov, Valentin Yu. Irkhin, Yulia A. Perevozchikova, Elena B. Marchenkova
Materials Science · Cross-listed from cond-mat.str-el
Multiple topological phases of magnons induced by Dzyaloshinskii-Moriya and pseudodipolar anisotropic exchange interactions in Kagome ferromagnets
Jin-Yu Ni, Xia-Ming Zheng, Peng-Tao Wei et al. (+2 more)
Kagome magnets naturally hosting Dirac points and flat bands exhibit novel topological phases, enabling rich interplays between interactions and
topologies. The discovery of two-dimensional (2D) magnets generally coexisting with different types of
magnetic interactions poses a challenge for topological magnonic manipulation. Here we investigate the topological
magnon phases of 2D Kagome ferromagnet with multiple
magnetic anisotropic interactions, i.e. Dzyaloshinskii-Moriya interaction (DMI) and pseudo-dipolar interaction (PDI). It is found that the different sole
magnetic anisotropic interactions introduce completely distinct topological phase diagrams and topological states. The multiple topological
magnon phases with high Chern number emerge due to the distinct anisotropic interactions. Moreover, the interplay of the multiple anisotropic DMI and PDI interactions involved with Dirac and flat bands controls a variety of topological phase transitions, implying greater manipulation potential. In addition, the sign reversal of thermal
Hall and Nernst conductivities induced by temperature is found in particular topological phase regions, namely topological origin, relating to the energy gap and Berry
curvature (Chern number) in the vicinity of
magnetic phase transition from the thermal fluctuations, providing a possible explanation for the experimental puzzles. All these results demonstrate that the novel topological magnonic properties in Kagome magnet with multiple
magnetic anisotropic interactions can realize a potential platform for magnonic devices and
quantum computing.
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All authors Jin-Yu Ni, Xia-Ming Zheng, Peng-Tao Wei, Da-Yong Liu, Liang-Jian Zou
Materials Science
Reductive Contact and Dipolar Interface Engineering Enable Stable Flexible CsSnI3 Nanowire Photodetectors
Letian Dai, Wanru Chen, Quanming Geng et al. (+4 more)
Lead-free tin-based halide perovskites are attractive for flexible and environmentally benign optoelectronics, but their application is limited by the rapid oxidation of Sn2+ to Sn4+ and poor operational stability. Here, we report a flexible CsSnI3 nanowire photodetector that achieves both high near-infrared photoresponse and long-term stability through synergistic aluminium-substrate contact engineering and dipolar interface modification. A 0.2 mm anodized aluminium foil serves as the flexible substrate, where localized
laser ablation exposes metallic aluminium regions that act as reductive sites, effectively suppressing Sn2+ oxidation during nanowire growth. Simultaneously, a polar interlayer of 3-fluoro-2-nitroanisole is introduced to improve energy-level
alignment, suppress interfacial deprotonation, and enhance charge extraction. The resulting device exhibits a responsivity of 0.39 A W-1, a specific detectivity of 1.38 * 10^13 Jones, and a wide linear dynamic range of 156 dB under 850 nm illumination. Moreover, the device retains over 85% of its initial photocurrent after 60 days in ambient air and maintains 94% of its initial photocurrent after 1000 bending cycles. This work establishes an effective strategy for stabilizing Sn-based perovskites toward high-performance flexible optoelectronic devices.
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All authors Letian Dai, Wanru Chen, Quanming Geng, Ying Xu, Guowu Zhou, Nuo Chen, Xiongjie Li
Materials Science
Magnetoelastic honeycomb fragmentation in VI$_{3}$
Enlin Shen, Tiberiu I. Popescu, Nishwal Gora et al. (+9 more)
The discovery of ordered magnetism in two-dimensional van der Waals materials at the monolayer limit challenges the Mermin-Wagner
theorem, which forbids spontaneous breaking of continuous
symmetries in two dimensions at finite temperatures. The persistence of static magnetism in low-dimensions is fundamentally influenced by
magnetic anisotropy and the local single-ion crystalline electric field. Crucially,
spin-orbit coupling connects the structural properties with
spin degrees of freedom. We investigate the
magnetic single-ion properties in the van der Waals magnet VI$_3$. Utilizing
neutron and x-ray diffraction, we map out the
symmetry breaking phase transitions and argue for a single structural transition at T$_S \sim$ 80 K, driven by an orbital degeneracy, followed by a
ferromagnetic transition at a lower temperature, T$_C \sim$ 50 K. Through a comparative analysis of samples prepared under varying conditions, we suggest that lower temperature transitions reported near $\sim$ 30 K are not intrinsic to VI$_{3}$. A group theoretical analysis suggests a structural transition from rhombohedral $R\overline{3}$ to triclinic $P\overline{1}$ or $P1$. This transition is significant as it suggests the formation of two distinct crystallographyically inequivalent V$^{3+}$ sites, each with distinct
spin-orbital properties.
Neutron spectroscopy provides evidence for dominant
magnetic exchange coupling only between
symmetry-equivalent sites in the triclinc unit
cell. We suggest this breaks up the low-temperature honeycomb VI$_3$
lattice into two interpenetrating approximately hexagonal planes resulting in a fragmentated honeycomb. Our findings highlight the critical role of magnetoelastic coupling in determining the
magnetic and structural phases in two-dimensional van der Waals magnets.
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All authors Enlin Shen, Tiberiu I. Popescu, Nishwal Gora, Guratinder Kaur, Edmond Chan, Harry Lane, Jose A. Rodriguez-Rivera, Guangyong Xu, Peter M. Gehring, Russell A. Ewings, Andy N. Fitch, Chris Stock
Materials Science
Benchmarking Universal Machine Learning Interatomic Potentials on Elemental Systems
Hossein Tahmasbi, Andreas Knüpfer, Thomas D. Kühne et al. (+1 more)
The rapid emergence of universal Machine Learning Interatomic Potentials (uMLIPs) has transformed materials modeling. However, a comprehensive understanding of their generalization behavior across configurational space remains an open challenge. In this work, we introduce a benchmarking framework to evaluate both the
equilibrium and far-from-
equilibrium performance of state-of-the-art uMLIPs, including three MACE-based models, MatterSim, and PET-MAD. Our assessment utilizes Equation-of-State (EOS) tests to evaluate near-
equilibrium properties, such as bulk
moduli and
equilibrium volumes, alongside extensive Minima Hopping (MH) structural searches to probe the global Potential Energy Surface (PES). Here, we assess universality within the fundamental limit of unary (elemental) systems, which serve as a necessary baseline for broader chemical generalization and provide a framework that can be systematically extended to multicomponent materials. We find that while most models exhibit high accuracy in reproducing
equilibrium volumes for transition metals, significant performance gaps emerge in alkali and alkaline earth metal groups. Crucially, our MH results reveal a decoupling between search efficiency and structural fidelity, highlighting that smoother learned PESs do not necessarily yield more accurate energetic landscapes.
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All authors Hossein Tahmasbi, Andreas Knüpfer, Thomas D. Kühne, Hossein Mirhosseini
Materials Science · Cross-listed from cond-mat.supr-con
Composition-Based Machine Learning for Screening Superconducting Ternary Hydrides from a Curated Dataset
Kazuaki Tokuyama, Souta Miyamoto, Taichi Masuda et al. (+1 more)
We present an ensemble machine-learning approach for composition-based, structure-agnostic screening of candidate
superconductors among ternary hydrides under high pressure. Hydrogen-rich hydrides are known to exhibit high superconducting transition temperatures, and ternary or multinary hydrides can stabilize superconducting phases at reduced pressures through chemical compression. To systematically explore this vast compositional space, we construct an ensemble of 30 XGBoost regression models trained on a curated
dataset of approximately 2000 binary and ternary hydride entries. The model ensemble is used to screen a broad set of A-B-H compositions at pressures of 100, 200, and 300 GPa, with screening outcomes evaluated statistically based on prediction consistency across ensemble members. This analysis highlights several high-scoring compositional systems, including Ca-Ti-H, Li-K-H, and Na-Mg-H, which were not explicitly included in the training
dataset. In addition, feature-importance analysis indicates that elemental properties such as ionization energy and atomic radius contribute significantly to the learned composition-level trends in superconducting transition temperature. Overall, these results demonstrate the utility of ensemble-based machine learning as a primary screening tool for identifying promising regions of chemical space in superconducting hydrides.
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All authors Kazuaki Tokuyama, Souta Miyamoto, Taichi Masuda, Katsuaki Tanabe
Materials Science
Turing Pattern Engineering Enables Kinetically Ultrastable yet Ductile Metallic Glasses
Huanrong Liu, Qingan Li, Shan Zhang et al. (+3 more)
Enhancing the kinetic stability of glasses often necessitates deepening thermodynamic stability, which typically compromises ductility due to increased structural
rigidity. Decoupling these properties remains a critical challenge for functional applications. Here, we demonstrate that pattern engineering in metallic glasses (MGs) enables unprecedented kinetic ultrastability while retaining thermodynamic metastability and intrinsic plasticity. Through atomistic simulations guided by machine-learning interatomic potentials and replica-exchange molecular dynamics, we reveal that clustering oxygen contents, driven by reaction-
diffusion-coupled pattern dynamics, act as localized pinning sites. These motifs drastically slow structural relaxation, yielding kinetic stability comparable to
crystal-like ultrastable glasses while retaining an energetic as-cast state. Remarkably, the thermodynamically metastable state preserves heterogeneous atomic mobility, allowing strain delocalization under mechanical stress. By tailoring oxygen modulation via
geometric patterning, we achieve an approximately 200 K increase in the onset temperature of the glass transition (Tonset) while maintaining fracture toughness akin to conventional MGs. This work establishes a paradigm of kinetic stabilization without thermodynamic compromise, offering a roadmap to additively manufacture bulk amorphous materials with combined hyperstability and plasticity.
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All authors Huanrong Liu, Qingan Li, Shan Zhang, Rui Su, Yunjiang Wang, Pengfei Guan
Materials Science
Low temperature magneto-transport and magnetic properties of MnSb$_2$Te$_4$ single crystals
V.N. Zverev, N.A. Abdullayev, Z.S. Aliev et al. (+6 more)
The results of a comprehensive study of MnSb$_2$Te$_4$ single
crystals are presented. The structure, Raman spectra, low-temperature transport,
Hall effect, magnetization, and
magnetic susceptibility are studied. It was established that the
crystals are
ferromagnetic, with a Curie temperature ranging from 22 to 45\,K for different samples.
Hall and magnetization measurements demonstrated that the system is a soft ferromagnet, which is of interest for practical applications.
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All authors V.N. Zverev, N.A. Abdullayev, Z.S. Aliev, I.R. Amiraslanov, Z.A. Jahangirli, I.I. Klimovskikh, A.A. Rybkina, A.M. Shikin, N.T. Mamedov
Materials Science
Linking Thermal History to Shear Band Interaction and Macroscopic Ductility in Metallic Glasses
Lechuan Sun, Shan Zhang, Bin Xu et al. (+3 more)
Shear band propagation and interaction are critical to the mechanical performance of metallic glasses and are strongly governed by thermal history, yet their microscopic mechanisms remain unclear. Here, using molecular dynamics simulations combined with a state-of-the-art annealing protocol, we systematically investigate these behaviors in a model metallic glass across effective quenching rates spanning six orders of magnitude. Through a double-notch model, we show that the normalized interaction distance relative to the single shear band width is significantly larger in slowly quenched samples than in rapidly quenched ones. Atomic-scale analysis reveals that rapidly quenched samples exhibit a high density of pre-existing soft regions, which trigger correlated shear transformation zones through local
vortex fields, resulting in propagation path locking and weak inter-band coupling. In contrast, slowly quenched samples exhibit enhanced structural heterogeneity and a right-shifted activation energy spectrum, promoting a single large-scale
vortex field ahead of the shear band front. This field facilitates long-range stress transmission and induces shear band deflection, convergence, and coalescence, a transition resembling a "shielding effect" in fracture mechanics, where
vortex-mediated disturbances destabilize the advancing shear band front. Our findings establish a direct microscopic connection between glass stability and shear-band-mediated plasticity and suggest that regulating shear band interactions offers a promising route to enhance the room-temperature ductility of metallic glasses.
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All authors Lechuan Sun, Shan Zhang, Bin Xu, Rui Su, Yunjiang Wang, Pengfei Guan
Materials Science
Geometry, electronic structure, and optical properties of boron cages: A first-principles DFT study
Kashinath T. Chavan, Ihsan Boustani and Alok Shukla
A systematic study of the structural, electronic, and optical properties of cage-like boron clusters, with the number of constituent atoms ranging from 20 to 122, has been carried out within the framework of density-functional theory (DFT), employing 6-31G(d, p) extended basis set. The dynamic stability of the clusters is analyzed through the vibrational frequency analysis, while to study the thermodynamic stability, we computed their binding energies per atom. The results suggest that the 32- and 92-atom cages are the most stable among the small and the large structures. The optical absorption spectra of these cages is computed using the time-dependent densityfunctional theory (TDDFT), which suggests their applications in optoelectronic devices in the visible range of the spectrum.
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Materials Science
Multi-state electromagnetic phase modulations in NiCo2O4 through cation disorder and hydrogenation
Xuanchi Zhou, Xiaohui Yao, Shuang Li et al. (+5 more)
One focal challenge in engineering low-power and scalable all-
oxide spintronic devices lies in exploring
ferromagnetic oxide material with perpendicular
magnetic anisotropy (PMA) and electronic conductivity while exhibiting tunable
spin states. Targeting this need, spinel nickel cobaltite (NiCo2O4, NCO), featured by room-temperature ferrimagnetically metallic ground state with strong PMA, emerges as a promising candidate in the field of
oxide spintronics. The cation distribution disorder inherent to NCO renders competing electromagnetic states and abnormal sign reversal of anomalous
Hall effect (AHE), introducing an additional freedom to adjust electromagnetic transports. Here, we unveil multi-state electromagnetic phase modulations in NCO system through controllable cation disorder and
proton evolution, extensively expanding electromagnetic phase diagram. The cation disorder in NCO tunable by growth temperature is identified as a critical control parameter for kinetically adjusting the
proton evolution, giving rise to intermediate hydrogenated states with chemical stability. Hydrogen incorporation reversibly drives structural transformation and electromagnetic state evolutions in NCO, with rich
spin-dependent correlated physics uncovered by combining the AHE scaling relation and synchrotron-based spectroscopy. Our work not only establishes NCO as a versatile platform for discovering
spin-dependent physical functionality but also extends the horizons in materials design for state-of-the-art spintronic devices harnessing magneto-ionic control and inherent cation disorder.
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All authors Xuanchi Zhou, Xiaohui Yao, Shuang Li, Xiaomei Qiao, Jiahui Ji, Guowei Zhou, Huihui Ji, Xiaohong Xu
Materials Science
Gauge-Invariant Long-Wavelength TDDFT Without Empty States: From Polarizability to Kubo Conductivity Across Heterogeneous Materials
Christian Tantardini, Quentin Pitteloud, Boris Yakobson et al. (+1 more)
Electromagnetic response is commonly computed in two
languages: length-gauge molecular polarizabilities and velocity-gauge (Kubo) conductivities for periodic solids. We introduce a compact, gauge-invariant bridge that carries the same microscopic inputs-transition dipoles and interaction kernels-from molecules to
crystals and heterogeneous media, with explicit SI prefactors and fine-structure scaling via $(\alpha_{\rm fs})$. The long-wavelength limit is handled through a reduced dielectric
matrix that retains local-field mixing, interfaces and 2D layers are treated with sheet boundary conditions (rather than naïve ultrathin films), and length-velocity equivalence is enforced in practice by including the equal-time (diamagnetic/contact) term alongside the paramagnetic current. Finite temperature is addressed on the Matsubara axis with numerically stable real-axis evaluation (complex polarization propagator), preserving unit consistency end-to-end. The framework enables predictive, unit-faithful observables from
radio frequency to ultraviolet-RF/microwave heating and penetration depth, dielectric-logging contrast, interfacial optics of thin films and 2D sheets, and adsorption metrics via imaginary-axis polarizabilities. Numerical checks (gauge overlay and optical $(f)$-sum saturation) validate the implementation. Immediate priorities include compact, temperature- and salinity-aware kernels with quantified uncertainties and operando interfacial diagnostics for integration into multiphysics digital twins.
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All authors Christian Tantardini, Quentin Pitteloud, Boris Yakobson, Martin Andersson
Materials Science
Ultrahigh Charge-to-Spin Conversion and Tunneling Magnetoresistance in Quasi-Two-Dimensional d-wave Altermagnet
Qing Zhang, Siyun Wang, Jianting Dong et al. (+1 more)
The emergence of altermagnets has driven groundbreaking advances in spintronics. Notably, d-wave altermagnets support non-relativistic
spin transport, efficient charge-to-
spin conversion, and T-odd
spin currents. In addition, their integration as electrodes in
antiferromagnetic tunnel junctions (AFMTJs) enables a tunneling magnetoresistance (TMR) effect, allowing electrical detection of Néel vectors for next-generation
memory devices. In this work, we investigate the non-relativistic
spin transport properties of the quasi-two-dimensional (quasi-2D) d-wave altermagnet KV\textsubscript{2}Se\textsubscript{2}O and the TMR effect in KV\textsubscript{2}Se\textsubscript{2}O-based AFMTJs via first-principles calculations. Our results reveal that KV\textsubscript{2}Se\textsubscript{2}O exhibits a non-relativistic longitudinal
spin polarization and a
spin Hall angle both exceeding 60% at room temperature, while KV\textsubscript{2}Se\textsubscript{2}O-based AFMTJs achieve a
giant TMR reaching approximately $10^{12}$%, which remains robust against
Fermi level shifts. These findings highlight the anisotropic
spin polarization inherent to d-wave staggered magnetism and underscore the critical role of
Fermi surface
topology in enhancing T-odd
spin transport and the TMR effect in AFMTJs.
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All authors Qing Zhang, Siyun Wang, Jianting Dong, Jia Zhang
Materials Science
Dielectric and gate metal engineering for threshold voltage modulation in enhancement mode monolayer MoS2 field effect transistors
Lixin Liu, Han Yan, Leyi Loh et al. (+8 more)
Excellent gate electrostatics in field effect transistors (FETs) based on two-dimensional transition metal dichalcogenide (2D TMD) channels can dramatically decrease static power dissipation. Energy efficient FETs operate in enhancement mode with small and positive threshold voltage (Vth) for n-type devices. However, most state-of-the-art FETs based on monolayer MoS2 channel operate in depletion mode with negative Vth due to doping from the underlying dielectric substrate. In this work, we identify key properties of the
semiconductor/dielectric interface (MoS2 on industrially relevant high dielectric constant (k) HfO2, ZrO2 and hBN for reference) responsible for realizing enhancement-mode operation of 2D MoS2 channel FETs. We find that hBN and ZrO2 dielectric substrates provide low defect interfaces with MoS2 that enables effective modulation of the Vth using gate metals of different work functions (WFs). We use photoluminescence (PL) and synchrotron X-ray photoelectron spectroscopy (XPS) measurements to investigate doping levels in monolayer MoS2 on different dielectrics with different WF gate metals. We complement the FET and spectroscopic measurements with capacitance-voltage analysis on dielectrics with varying thicknesses, which confirm that Vth modulation in ZrO2 devices is correlated with WF of the gate metals - in contrast with HfO2 devices that exhibit signatures of Vth pinning induced by
oxide/interface defect states. Finally, we demonstrate FETs using a 2D MoS2 channel and a 6 nm of ZrO2 dielectric, achieving a subthreshold swing of 87 mV dec-1 and a threshold voltage of 0.1 V. Our results offer insights into the role of dielectric/
semiconductor interface in 2D MoS2 based FETs for realizing enhancement mode FETs and highlight the potential of ZrO2 as a scalable high-k dielectric.
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All authors Lixin Liu, Han Yan, Leyi Loh, Kamal Kumar Paul, Soumya Sarkar, Deepnarayan Biswas, Tien-Lin Lee, Takashi Taniguchi, Kenji Watanabe, Manish Chhowalla, Yan Wang
Materials Science
Microscopic and spectroscopic evidences for multiple ion-exchange reactions controlling biomineralization of CaO.MgO.2SiO2 nanoceramics
R. Vahedifard and E. Salahinejad
This study is focused on the mechanism of in vitro biomineralization on the surface of CaO.MgO.2SiO2 (diopside) nanostructured coatings by scanning electron microscopy, energy-dispersive X-ray spectroscopy and inductively coupled
plasma spectroscopy assessments. A homogeneous diopside coating of almost 2 um in thickness was deposited on a medical-grade stainless steel by coprecipitation, dipping and sintering sequences. After soaking the sample in a simulated body fluid (SBF) for 14 days, a layer with the thickness of 8 {\mu}m is recognized to be substituted for the primary diopside deposit, suggesting the mineralization of apatite on the surface. Investigations revealed that the newly-formed layer is predominantly composed of Ca, P and Si, albeit with a biased accumulations of P and Si towards the surface and substrate, respectively. The variations in the ionic composition and pH of the SBF due to the incubation of the sample were also correlated with the above-interpreted biomineralization. In conclusion, the multiple ion-exchange reactions related to Ca, Mg, Si and P were found to be responsible for the in vitro bioactivity of nanodiopside.
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