Materials Science
Stoichiometric Epitaxial Strontium Titanate Thin Films on Silicon by High-Temperature Sr Segregation
Andries Boelen, Marina Baryshnikova, Maxim Korytov et al. (+4 more)
Thin-film strontium titanate (SrTiO$_3$, STO) layers grown on silicon require accurate stoichiometry and single-crystalline order to exploit their functional properties optimally.
Oxide molecular beam epitaxy can provide an epitaxial interface, but suffers from source oxidation and resulting flux instabilities, yielding only a narrow growth process window for cationic stoichiometry control. Here, we investigate post-growth annealing in oxygen as a pathway to drive the STO layer toward stoichiometry in intentionally Sr-rich epitaxial STO films on silicon (001). Annealing over a broad temperature range revealed two distinct Sr-segregation mechanisms. Below 800 {\deg}C, excess Sr segregates toward the surface, forming SrO outgrowths that progressively sublimate at elevated temperatures. Above 800 {\deg}C, a second mechanism dominates: Sr accumulates within the interfacial SiO$_2$ layer formed by oxygen
diffusion at the STO/Si interface. Together, these mechanisms effectively remove excess Sr from the STO
lattice, yielding a more stoichiometric perovskite layer. Our results demonstrate that growing slightly Sr-rich STO templates followed by controlled annealing provides a practical route to improve crystalline quality, offering a scalable strategy for high-quality STO integration on silicon.
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All authors Andries Boelen, Marina Baryshnikova, Maxim Korytov, Sean R. C. McMitchell, Felix Cahyadi, Christian Haffner, Clement Merckling
Materials Science · Cross-listed from cond-mat.stat-mech
Excess energy fluctuations with applications to deviations from Debye's specific heat
Ralph V. Chamberlin and Sumiyoshi Abe
Measured specific heats often exceed Debye's T^3-law, even in high-purity single
crystals. Analogous excess energy fluctuations are found in molecular dynamics (MD) simulations of
crystals with no defects. Here, a theory is developed for the fluctuations based on rapid modulation of the ground-state energy due to the motion of next-nearest-neighbor atoms. Crucially, the modulations must be adiabatic, with time- and phase-averaging before thermal averaging, consistent with evidence from the simulations and multiple experimental techniques showing that localized excitations are decoupled from the heat bath. Emergent nonextensivity is interpreted by analogy with anomalous
diffusion. The theory modifies the standard relation between energy fluctuations and specific heat, giving good agreement with the simulations and new insight into many measurements. The theory may also provide a basis for understanding excess specific heat in amorphous materials and anomalous noise in
quantum devices.
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Materials Science
Predicting Physical and Physical-Chemical Properties of Molecular-Based Materials Using Computational Neural Networks
Andrei A. Gakh, Bobby G. Sumpter and Donald W. Noid
A computational scheme, which utilizes neural networks, was developed to predict properties of molecular-based materials from chemical structures. The method uses a set of simple
algorithms to encode the structure and composition of organic molecules directly into numerical vectors, which is used as input for neural networks. Backpropagation type neural networks are then used to correlate these numeric inputs with a set of desired properties. Calculated results for a series of hydrocarbons, hydrofluorocarbons, and crown ethers demonstrate average accuracies of 0.2-8.1% with maximum deviations of 16-20% for a broad range of thermodynamic, physical, and physical-chemical characteristics (heat capacity, enthalpy, heat of evaporation, boiling point, density, refractive index, stability constants, etc.). In addition, a number of physical and mechanical properties were estimated for polymeric materials and compared with regression analysis. Based on the neural network capabilities of formulating accurate quantitative structure property relationships, a technique called computational synthesis is suggested for performing materials design.
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Materials Science
Controlled component segregation in vapor-deposited organic semiconductor glass mixtures
Shinian Cheng, Yejung Lee, Lian Yu et al. (+3 more)
Multicomponent vapor-deposited organic glasses are essential in organic electronic applications, but achieving controlled component segregation at the nano- and mesoscale remains a challenge, hindering the rational development of high-performance devices. In this study, we investigate binary organic
semiconductor mixtures of TPD (N,N'-Bis(3-methylphenyl)-N,N'-diphenylbenzidine) and TCTA (Tris(4-carbazoyl-9-ylphenyl)amine). Despite being miscible in the bulk
liquid state, the co-deposited glassy films of these two organic
semiconductors exhibit a range of segregation behaviors, from homogenous to clearly phase-separated structures. We employed differential scanning calorimetry and resonant soft X-ray scattering (RSoXS) to study the component segregation behavior and used the National Institute of Standards and Technology RSoXS Simulation Suite, paired with Atomic Force Microscopy, to interpret the energy-dependent RSoXS spectra. Our results indicate that component segregation in co-deposited TPD-TCTA films is due to a kinetically-arrested nucleation-and-growth mechanism, in contrast to the segregation mechanism of a previously reported TPD-DO37 (disperse orange 37) mixture which is strongly immiscible in bulk. This work provides a demonstration of tunable molecular aggregation in organic
semiconductor glasses, enabling access to a continuum of morphologies from homogeneously mixed to segregated phases.
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All authors Shinian Cheng, Yejung Lee, Lian Yu, Mark D. Ediger, Dean M. DeLongchamp, Camille E. Bishop
Materials Science
First-principles description of pumped inelastic X-ray scattering: example of K-edge RIXS in graphite
Elias Richter, Benedikt Maurer and Claudia Draxl
We present an $\textit{ab initio}$ framework for predicting resonant inelastic X-ray scattering (RIXS) in optically pumped materials. Our methodology is based on the Kramers-Heisenberg formula for the double-differential cross section formulated using the results of the Bethe-Salpeter equation (BSE) from many-body perturbation theory. To extend this approach to the time domain, we incorporate non-
equilibrium charge-carrier distributions obtained from real-time, time-dependent density-functional theory (RT-TDDFT). Generalizing the RIXS implementation with respect to arbitrary polarizations, allows us to consider different orientations of incoming and outgoing light. We demonstrate our method's capabilities by studying RIXS at the K-edge of graphite for various non-
equilibrium charge-carrier distributions, representing different delay times after optical pumping. Our results reveal angular dependencies in $\pi$- and $\sigma$-orbital-derived spectral regions, in good agreement with experiment.
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Materials Science
An Extensible Agentic Framework for Expert-Level Automation of Atomistic Simulations
Yutack Park, Yeonwoo Chung, Jinmu You et al. (+3 more)
Traditionally, atomistic simulation has been constrained by the computational scaling limits of ab initio methods and the parameterization overhead of empirical force fields. The recent emergence of universal machine learning interatomic potentials has significantly mitigated these bottlenecks, offering near-
quantum accuracy and generalizability across diverse chemical spaces at a fraction of the computational cost. However, this shift has relocated the bottleneck to the human dimension: time-consuming mechanical processes, such as input preparation and data analysis, now dominate the research lifecycle. We introduce Paimon, a Platform for Agentic Integration in Materials Optimization and Nanoscale-simulations. Through hundreds of trials on an expert-level
liquid electrolyte simulation, we show that Paimon substantially improves the reliability of agentic workflows by suppressing silent errors: plausible yet physically incorrect results. Paimon accommodates a new capability without modifying the
agents already present, which we demonstrate by integrating an externally developed scientific
agent. As an
agent harness for atomistic simulations, Paimon affords researchers a continuous, science-centric workflow throughout the entire simulation lifecycle.
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All authors Yutack Park, Yeonwoo Chung, Jinmu You, Jisu Kim, Suyeon Ju, Seungwu Han
Materials Science
Context-Aware Deep Learning for Defect Classification in Atomic-Resolution STEM
Jiadong Dan, Cheng Zhang, Leyi Loh et al. (+5 more)
Artificial intelligence is rapidly advancing materials characterization, yet most applications in electron microscopy rely solely on image contrast, overlooking the chemical and experimental context that shapes image formation. This limitation makes defect classification inherently ambiguous, as similar contrasts can arise from different materials or imaging conditions. Here we develop a context-aware learning framework that integrates image-derived contrast with metadata describing composition, beam energy, and detector geometry. Using a systematically constructed
dataset of ~55 million simulated patches spanning 576 cases across 96 doped monolayer transition-metal dichalcogenides, we show that conditioning on contextual variables transforms defect classification from an ill-posed image-only task into a well-posed, physically grounded problem. The framework achieves over 98% accuracy on simulations and near-human agreement on experimental data, with a 94% reduction in posterior
entropy. By emphasizing contextual grounding over architectural complexity, this approach links experimental image contrast to the underlying chemical and imaging conditions, supporting physically grounded defect assignments and a general pathway toward
multimodal AI models for autonomous materials characterization.
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All authors Jiadong Dan, Cheng Zhang, Leyi Loh, Ivan Verzhbitskiy, Yuan Chen, Goki Eda, Michel Bosman, N. Duane Loh
Materials Science
Hydride formation and phase separation in palladium nanoparticles from a transferable atomic cluster expansion potential
Minaam Qamar, Apinya Ngoipala, Matous Mrovec et al. (+2 more)
The palladium-hydrogen system is a prototype for hydrogen-metal interactions and underpins technologies such as hydrogen storage, catalysis and purification. Yet its nanoscale behaviour – where surface and interface energetics, elastic coherency strain and size-dependent thermodynamics govern phase separation – has eluded accurate atomistic simulation. Empirical potentials misrepresent the energetics of interstitial hydrogen, while existing machine-learning models are restricted to bulk phases at low-hydrogen environments. Here we introduce an atomic cluster expansion (ACE) for Pd-H that reproduces formation energies,
phonon spectra, elastic constants, hydrogen migration barriers and surface adsorption with near-DFT accuracy, benchmarked directly against
neutron-scattering, high-pressure and
lattice-expansion experiments. Its near-linear scaling and CPU efficiency make molecular dynamics of PdH$_x$ nanoparticles exceeding 28,000 atoms ($\sim$12 nm in diameter) tractable over nanosecond timescales. These simulations resolve, at the atomic scale, the kinetic separation of $\alpha$- and $\beta$-PdH$_x$ into a core-shell architecture, reproduce the experimentally observed size dependence of the
lattice parameter, and uncover a pronounced hydrogen-induced lowering of the nanoparticle melting temperature. The potential brings experimentally relevant scales of metal-hydride dynamics within quantitative reach.
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All authors Minaam Qamar, Apinya Ngoipala, Matous Mrovec, Matthias Vandichel, Ralf Drautz
Materials Science
Group theory of Raman effect in magnetic materials
Rui-Chun Xiao, Xue Liu, Yuxuan Jiang et al. (+5 more)
Despite the wealth of experimental observations on Raman scattering in
magnetic materials, the underlying selection rules have remained largely unexplored. In this work, we use Onsager reciprocity relation, other than the conventional corepresentation method, to deal with the mathematical structures of Raman tensors in
magnetic groups. Using this approach, we generate Raman tensor tables for all
magnetic point groups, and present a comprehensive understanding of the Raman selection rules in
magnetic materials with direct product representations method. Our theoretical and numerical results match previous experiments well, and resolve a recent puzzle in the Raman spectroscopy of CrSBr. Moreover, we identify a common but overlooked phenomenon: the magneto-Raman vector can be orthogonal to the
magnetic moment direction. Our method and associated Raman tensor tables will be helpful for the Raman studies in both experimental and theoretical domains.
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All authors Rui-Chun Xiao, Xue Liu, Yuxuan Jiang, Hang Zhou, Zi-Hao Feng, Jie Hou, Xiangru Kong, Yujun Zhang
Materials Science
Crystal Shape and Lattice Deformation in Powder Diffraction
Matteo Leoni and Alberto Leonardi
Accurate modelling of diffraction peak shapes is essential for extracting microstructural information from nanocrystalline materials. Common-volume functions are widely used to describe finite-size and shape broadening in powder diffraction, but analytical expressions are available only for a limited set of ideal geometries. Here, we introduce a generalized
Fourier-based framework in which
crystal-domain shape deformation,
lattice deformation, and relative shape-
lattice misorientation are treated as independently refinable tensor operations within a unified formalism. The approach enables continuous affine transformations of both
crystal shape and
lattice base while preserving analytical evaluation of directional
Fourier coefficients. As a result, complex particle shapes, anisotropic deformations, and arbitrary relative orientations between shape and
lattice can be modelled within a single reciprocal- and real-space framework, including coupled shape-
lattice transformations not accessible using conventional powder diffraction line-profile methods. The formalism can be applied to individual diffraction peaks, full powder patterns, and total-scattering shape corrections. Validation against virtual scattering experiment data demonstrates that
crystal size, shape,
lattice deformation, and relative shape-
lattice orientation can be simultaneously recovered with high accuracy.
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Materials Science · Cross-listed from cond-mat.mes-hall
Unconventional incommensurate epitaxy of superconducting FeSe films on SrTiO$_3$
M. Klement, K. M. Fijalkowski, M. Kamp et al. (+2 more)
We present a combined X-ray diffraction and transmission electron microscopy study of superconducting FeSe/FeTe multilayers grown by molecular beam epitaxy on SrTiO$_3$(001) substrates. While X-ray diffraction confirms perfect in-plane epitaxial
alignment between FeSe, FeTe, and the substrate, scanning transmission electron microscopy reveals a surprising lack of atomic registry at the FeSe/SrTiO$_3$ interface. Instead of adapting to the substrate
lattice, FeSe retains its own in-plane
lattice spacing. A periodic lateral shift between the atomic positions of FeSe and SrTiO$_3$ is observed, with a registry recurrence length that matches the
lattice mismatch determined by X-ray diffraction. No misfit dislocations or other relaxation features are detected at the interface. This coexistence of directional
alignment and registry-free growth suggests an unconventional regime of epitaxy in which crystallographic orientation is maintained without atomic matching. The findings offer insight into strain accommodation in layered systems and may have implications for interface engineering in Fe-based
superconductors.
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All authors M. Klement, K. M. Fijalkowski, M. Kamp, C. Gould, L. W. Molenkamp
Materials Science
Layer-parity-defined surface polarization in Nb$_3$Cl$_8$ for excitonic modulation at van der Waals interfaces
Xinyue Huang, Hansheng Xu, Yuchen Gao et al. (+10 more)
The intrinsic
symmetry breaking in the breathing kagome
lattice of layered Nb$_3$Cl$_8$ provides a unique mechanism for realizing electrically polar surfaces. In each monolayer, the trimerization of Nb atoms breaks inversion and mirror
symmetries, generating an out-of-plane electric dipole. The AB-stacked $\alpha$ phase arranges adjacent layer dipoles antiferroelectrically, leaving the uncompensated surface polarization strictly governed by layer parity. Here, using atomic force microscopy operated in Kelvin probe force microscopy mode, we directly visualize layer-dependent polarization states in exfoliated Nb$_3$Cl$_8$ flakes and resolve a pronounced odd-even oscillation of the surface electrostatic potential. Beyond this parity-locked antiferroelectric order, we further identify intralayer polar domains in which local atomic reconstructions of the breathing kagome network reverse the out-of-plane dipole of the surface layer, producing ferroelectric-like stacking configurations. By interfacing monolayer MoSe$_2$ with Nb$_3$Cl$_8$, we demonstrate that these surface-polarization textures effectively modulate adjacent excitonic emission through domain-dependent interfacial band
alignment and charge transfer. Our findings establish Nb$_3$Cl$_8$ as an intrinsic layer-polarized van der Waals platform and show that layer parity provides powerful structural degree of freedom for programming excitonic and optoelectronic responses at van der Waals interfaces.
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All authors Xinyue Huang, Hansheng Xu, Yuchen Gao, Yushen Zhou, Zhijie Ma, Kenji Watanabe, Takashi Taniguchi, Zuxin Chen, Jianqi Huang, Jianpeng Liu, Teng Yang, Youguo Shi, Yu Ye
Materials Science · Cross-listed from cond-mat.soft
Ivan I. Smalyukh and Mykola Tasinkevych
In soft condensed matter,
curvature does more than simply distort an ordered medium: it helps select defect structures, redistribute elastic stress, bias chirality, and guide self-assembly. This review examines how curved, multiply connected, and knotted boundaries in
liquid-
crystal colloids and confined nematics generate topological defects and localized solitonic textures, and how these structures mediate interactions between mesoscale building blocks. We introduce a unifying framework based on genus, Euler characteristic, anchoring, and chirality, and use it to discuss spherical, handlebody, and boundary-bearing colloids, together with droplets and
polymer-dispersed nematics of nontrivial
topology. Particular emphasis is placed on the interplay of geometry and
topology in determining boojums, disclination loops, hedgehog charges, and linked and knotted defect structures. We then turn to
chiral systems hosting skyrmions, torons, hopfions, and related localized textures, highlighting how chirality and confinement stabilize three-dimensional topological states. Finally, we discuss how these concepts translate into design principles for controlled self-assembly, templating, and functional composite materials. More broadly, we argue that
liquid-
crystal colloids and confined nematics provide experimentally accessible model systems in which
curvature,
topology, and chirality can be harnessed as programmable tools for designing organized soft matter.
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Materials Science
The impact of interfacial chemistry on the band offset of GaAs/Ga$_2$O$_3$ heterostructures
Sofia Apergi, Alfredo Pasquarello, Charles Cornet et al. (+1 more)
Ga$_2$O$_3$/GaAs heterojunctions are emerging as promising candidates for next-generation power electronics, photonics, and energy devices, leveraging the high breakdown voltage and thermal stability of Ga$_2$O$_3$ alongside the mature technology, high hole mobility, and higher refractive index of GaAs. The efficiency of these devices depends strongly on the band
alignment between the two materials, however both type-I and type-II
alignment have been reported in the literature for these
heterostructures. To address this ambiguity, we use hybrid density functional theory to systematically investigate the band
alignment at GaAs/Ga$_2$O$_3$ interfaces, focusing on the role of interface chemistry. By considering Ga-O-, As-, and As-O-rich interfaces both in amorphous and crystalline Ga$_2$O$_3$ phases, we demonstrate that interface stoichiometry determines the
alignment type: Ga-O-rich interfaces exhibit type-II
alignment with large valence band offsets (~3.1 eV), while As-rich and As-O-rich interfaces favor type-I
alignment with reduced offsets (~2.3-2.6 eV). These trends are attributed to interface dipole formation driven by bonding configuration. Our findings provide insight into the relationship between chemistry and band
alignment in GaAs/Ga$_2$O$_3$
heterostructures, enabling targeted optimization for specific device applications.
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All authors Sofia Apergi, Alfredo Pasquarello, Charles Cornet, Laurent Pedesseau
Materials Science
Metal Halide Perovskite/Chalcohalide Heterojunctions for the Photoinduced Oxidative Coupling of p-substituted Thiophenols
Anna Cabona, Stefano Toso, Alejandro Cortés-Villena et al. (+7 more)
The introduction of a
semiconductor-
semiconductor junction is an effective strategy to enhance the photocatalytic performance of perovskite nanocrystal-based systems. Herein, we optimized the synthesis of CsPbX3/Pb4S3X2 (X= Cl, Br, I) perovskites-chalcohalides
heterostructures, whose band
alignment can be tuned by halide composition. As a proof-of-concept, we evaluated the photooxidative coupling of p-substituted thiophenols at room temperature, under visible-light, air, and without sacrificial electron donor. Notably, CsPbBr3/Pb4S3Br2 achieved up to 94 % selectivity toward disulfide (p-OCH3 thiophenol with a turnover number of 14300) highlighting the crucial role of the type-II heterojunction to promote charge separation and efficient electron delocalization across the junction.
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All authors Anna Cabona, Stefano Toso, Alejandro Cortés-Villena, Ignacio Rosa-Pardo, Mirko Prato, Michele Ferri, Julia Perez-Prieto, Ilka Kriegel, Liberato Manna, Raquel E. Galian
Materials Science
BSE+ calculations for 2D materials: a unified description of excitons and plasmons
Amalie H. Svaneborg and and Kristian S. Thygesen
The Bethe-Salpeter equation (BSE) accurately describes low-energy optical spectra in materials with strong excitonic effects, but its high computational cost limits the number of electron-hole transitions that can be included. Neglecting high-energy transitions leads to an underestimation of the real part of the dielectric function, often producing a spurious plasmon peak in the BSE electron energy loss spectrum (EELS). The recently introduced BSE+ method addresses this by combining a four-point BSE-like equation for the irreducible polarisability with a two-point Dyson equation that includes the high-energy transitions at the Random Phase Approximation (RPA) level. Here, we present a detailed account of the method, extend it to two-dimensional materials, and apply it to a set of transition metal dichalcogenide monolayers. BSE+ preserves the excitonic features of the BSE at low energies while reproducing the plasmonic structure of the RPA at higher energies, yielding good agreement with experimental EELS data across the full energy range and strongly suppressing the spurious plasmon. BSE+ converges much faster than BSE with respect to the electron-hole basis size, at a comparable computational cost, and is implemented in the GPAW code.
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Materials Science · Cross-listed from cond-mat.str-el
Designing electronic magnetoelectric matter with organic quantum spin trimers
Yuko Hosokoshi, Christopher P. Aoyama, Zhuowei Zhang et al. (+17 more)
Magnetoelectric (ME) phenomena are commonly driven by
spin-
lattice coupling. Here we demonstrate a different route based on frustrated
quantum spin trimers that intrinsically intertwine
magnetic moments and electric dipoles. Using molecular design principles, we realize a weakly coupled
lattice of equilateral $S=1/2$
spin trimers in the organic radical
crystal TNN$\cdot$CH$_3$CN. In this material, correlated electronic fluctuations within each trimer generate electric dipoles, while geometrically frustrated intertrimer interactions organize them into collective ME states. Magnetization, thermodynamic, and dielectric measurements reveal multiple
magnetic-field-induced phases, including the $1/3$-magnetization plateau marked by pronounced dielectric anomalies. Effective low-energy theories and numerical simulations show that these phenomena are driven by electronically generated trimer dipoles whose collective order is stabilized by frustration relief of the intertrimer interactions, establishing a direct connection between
geometric frustration and emergent magnetoelectricity. Our results identify
quantum spin trimers as multifunctional building blocks, providing a bottom-up route for designing correlated ME materials from electronically active
quantum spin clusters.
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All authors Yuko Hosokoshi, Christopher P. Aoyama, Zhuowei Zhang, Toshio Ono, Kosuke Takada, Ayaka Higashiguchi, Seitaro Iisaka, Koudai Yamasaki, Hironori Yamaguchi, Shengzhi Zhang, Mohammad Irfan, Minseong Lee, Eun Sang Choi, Yasuyuki Shimura, Toshiro Sakakibara, Zhiyuan Xie, Hiroki Nakano, Yasu Takano, Cristian D. Batista, Yoshitomo Kamiya
Materials Science
Artificial Intelligence for Instability in Inorganic Perovskites: From Mechanism Discovery to Engineering Strategies
Xue Zhao, Chuan-Xin Cui, Zi-Hao Xu et al. (+3 more)
Three-dimensional all-inorganic halide perovskites, represented by CsPbX$_3$ (X = Cl, Br, I), have attracted broad interest in photovoltaics, photodetectors, and light-emitting devices because of their outstanding optoelectronic properties. Their practical deployment, however, remains limited by instability under thermal, chemical, optical, and electrical stress. Conventional studies have established important experimental and theoretical foundations, but they still struggle with
multimodal data, coupled degradation pathways, protocol dependence, sparse statistics, and uncertainty quantification. Artificial intelligence (AI) offers a practical route to address these limitations. This review summarizes recent progress in AI-assisted studies of instability in 3D CsPbX$_3$ and organizes the discussion around four linked tasks, including stability discrimination and diagnosis, microscopic mechanism analysis, consequence and reliability modeling, and engineering stability enhancement. We further discuss the main limitations of current methods, especially in data quality, protocol consistency,
benchmark design, interpretability, and transferability across domains. Finally, we outline future directions for the field, including standardized data infrastructures, interpretable cross-scale models, and tighter integration of AI with automated experiments and physics-based modeling. The aim of this review is to provide a coherent and practically useful framework for researchers seeking to use AI to understand, predict, and mitigate instability in inorganic perovskites.
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All authors Xue Zhao, Chuan-Xin Cui, Zi-Hao Xu, Yuan-Long Pang, Jun-Jie Li, Jin-Wu Jiang
Materials Science
Molecular dynamic simulation of multicomponent CoCrFeNiMn high-entropy alloy thin film deposition
Oleksandr I. Kushnerov, Sergey I. Ryabtsev and Valerij F. Bashev
The deposition and growth of a thin CoCrFeMnNi high-
entropy alloy film on an Al(100) substrate were investigated by molecular dynamics simulation. Interatomic interactions were described using a calibrated set of Morse potentials combined with mixing rules for regular solutions. During a 100 ns simulation, 50,000 atoms with an incident energy of 10 eV were deposited, producing a film of about 6.1 nm thickness. The resulting film contains face-centred cubic (FCC), body-centred cubic (BCC), hexagonal close-packed (HCP), and amorphous regions. Analysis of the radial distribution function (RDF) was used to determine nearest-neighbour distances and estimate
lattice parameters for the crystalline phases. The simulated phase composition and structural parameters are in good agreement with available experimental data.
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Materials Science
Symmetry-Breaking Induced Spin Transport and Magneto-Optical Regulation in 2D Altermagnet Ru2MoSe4
Wenpeng Wang, Hang Shi, Yuping Tian et al. (+2 more)
Two-dimensional (2D) altermagnets (AMs) offer a compelling paradigm for advanced spintronics, yet their fully compensated macroscopic
spin currents inherently limit practical device integration. In this work, using first-principles calculations and theoretical analysis, we demonstrate that the 2D material Ru2MoSe4 hosts AM ground state protected by S4zT
symmetry. Using uniaxial strain modulation and stacking configuration, we show that the monolayer and the AC-stacking
bilayer Ru2MoSe4 host fully
spin-polarized currents, piezomagnetically induced net magnetization, and the magneto-optical Kerr effect. Our findings establish Ru2MoSe4 as a tunable platform, offering a feasible mechanism to simultaneously trigger electrical
spin transport signals and amplify optical readout signatures for next-generation spintronics and valleytronics.
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All authors Wenpeng Wang, Hang Shi, Yuping Tian, Wei-Jiang Gong, Xiangru Kong
Materials Science
Precipitate phase selection and grain boundary morphology in Cu-Ni-Si-Mn alloys: A machine-learning interatomic potential study
Aadil Fayaz Wani, Il-Seok Jeong, Haekwan Jeon et al. (+6 more)
Alloys inevitably contain interphase boundaries, whose energetics govern nucleation processes and precipitate morphology. In Cu-Ni-Si
alloys, Mn addition markedly changes grain boundary (GB) precipitation behavior. While GB precipitation of stable Ni$_2$Si in Mn-free
alloys is associated with degraded mechanical properties, Mn addition instead promotes film-shaped Mn$_6$Ni$_{16}$Si$_7$ (G-phase) precipitation, which is correlated improved mechanical properties. However, the atomic origin of the contrasting GB phase selection and morphology remains unclear. Here we perform machine-learning interatomic potential (MLIP) calculations to investigate the effect of interphase-boundary atomic structure on GB precipitates in Cu-Ni-Si
alloys with and without Mn. The MLIP calculations reliably reproduce DFT-level energetics for interfacial bonding and microstructural configurations, and further predict that Mn addition favors GB precipitation of Mn$_6$Ni$_{16}$Si$_7$ rather than Ni$_2$Si. Experimentally, Mn-free
alloys are observed to exhibit irregularly-shaped Ni$_2$Si precipitates with open-boundary-like Cu/Ni$_2$Si interfaces, whereas Mn-added
alloys exhibit film-like G-phase at GBs. Large-scale atomistic interface calculations reveal that the coherent interface structure between Cu and Ni$_2$Si favors the formation of plate-like strained Ni$_2$Si precipitates in the
matrix. Upon coarsening and stress release, an out-of-phase coherent-like interface can form at GBs, generating a local repulsive region that gives rise to surface-like open-boundary structures and explains the irregular morphology of GB stable Ni$_2$Si precipitates. In contrast, Cu/Mn$_6$Ni$_{16}$Si$_7$ interfaces remain predominantly incoherent with moderate boundary energies and no pronounced repulsive regime, thereby stabilizing continuous interfacial contact and explaining film-shaped GB precipitation.
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All authors Aadil Fayaz Wani, Il-Seok Jeong, Haekwan Jeon, Jaesun Kim, SuDong Park, Eun-Ae Choi, Seung Zeon Han, Seungwu Han, Byungki Ryu
Materials Science · Cross-listed from cond-mat.mes-hall
Valley-Landscape Engineering in Bilayer WSe$_2$ Gate-All-Around Transistors
Katsunori Wakabayashi, Souren Adhikary and Kazuhito Tsukagoshi
The K-$\Gamma$ valence-band splitting $\Delta_{K\Gamma}$ that governs hole transport in few-layer WSe$_2$ is not a fixed material constant. It is tuned by interlayer stacking, strain, pressure, and the dielectric and displacement-field environment. Its computed value also depends on the level of electronic-structure theory.
Bilayer WSe$_2$ therefore realizes a tunable multivalley landscape rather than a single operating point. We combine first-principles inputs with an analytical two-valley device model for gate-all-around (GAA) field-effect transistors, and obtain three results. (i) The minimum subthreshold swing stays near the thermionic limit of $60$~mV~dec$^{-1}$ independently of layer number, because well below threshold the
quantum capacitance remains far below the
oxide capacitance. (ii) The effective mobility is set by the K-to-$\Gamma$ occupation ratio: valley redistribution is strong when $\Delta_{K\Gamma}$ is of order $k_BT$ and fades toward single-valley $K$ transport as the splitting grows. (iii) In this small-splitting regime, biaxial strain tunes the effective mobility - and hence the on-current - through the valley population while the subthreshold swing stays at the thermionic limit, decoupling mobility control from electrostatic switching in a way distinct from scattering-based strategies. A symmetric GAA gate controls carrier density at essentially fixed splitting, and because an out-of-plane field increases $\Delta_{K\Gamma}$, its midplane-symmetric potential avoids driving the channel out of the small-splitting regime. The design principle has two facets: small $\Delta_{K\Gamma}$ - set by layer number, stacking, strain, and dielectric engineering - maximizes the valley tunability of $\mu_\mathrm{eff}$, whereas larger $\Delta_{K\Gamma}$, for example through compressive strain, suppresses the heavy $\Gamma$ valley and maximizes the on-state mobility.
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Materials Science
Chemical tuning of magnetic ordering and cryogenic magnetocaloric response in zircon-type Gd1-xErxVO4
Ming Zeng, Muqing Su, Liang Ming et al. (+4 more)
Chemical substitution offers an effective route to tune
magnetic ordering and magnetocaloric performance in rare-earth
oxides for cryogenic refrigeration. Here we investigate the structural evo lution,
magnetic properties, and magnetocaloric effect of polycrystalline zircon-type Gd1-xErxVO4 (x=0, 0.1, 0.25, 0.5, and 0.75). Powder X-ray diffraction confirms that all samples crystallize in the tetragonal zircon structure without detectable
impurity phases. Substitution of Gd3+ by the smaller Er3+ ion produces a systematic
lattice contraction and modifies the
magnetic behavior of the rare-earth sublattice. In particular, the
magnetic ordering temperature is suppressed from 3.65(2) K in GdVO4 to 2.76(2) K in Gd0.9Er0.1VO4 , accompanied by a weakening of the
spin-flop-like field-induced anomaly observed in the parent compound. A low Er concentration correspondingly improves the low-temperature magnetocaloric performance, with Gd0.9Er0.1VO4 exhibiting a max imum
magnetic entropy change of 45.1 J kg-1 K-1 for mu_0 Delta H=7T. These results demonstrate that weak Er substitution effectively tunes the competition among exchange interactions, dipolar coupling, and
magnetic anisotropy, optimizing the balance between
magnetic ordering and available
spin entropy in zircon-type rare-earth vanadates, which is crucial for developing efficient cryogenic refrigeration materials.
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All authors Ming Zeng, Muqing Su, Liang Ming, Xiaolong Yang, Wang Chen, Lingwei Li, Hai-Feng Li
Materials Science
Local electronic structure and dynamics of hydrogen in $\text{CeO}_2$
A. Koda, T. U. Ito, M. Hiraishi et al. (+2 more)
The local electronic states of
muon (Mu) as an isotope of hydrogen (H) in high-quality single-crystalline ceria (CeO$_2$) are investigated using
muon spin rotation/relaxation ($\mu\text{SR}$) and first-principles density functional theory (DFT) calculations. Upon positive
muon implantation, both paramagnetic (Mu$^0$) and diamagnetic (Mu$^*$) states are observed below $\approx$10 K.
Magnetic field dependence of the Mu$^0$ signals combined with DFT results provides evidence for the formation of a polaron state, consisting of Mu bonded to a ligand oxygen and a $4f$ electron localized on a nearby Ce site. The
crystal-orientation dependence of the Mu$^0$ signal suggests strong anisotropy of the $4f$ electron due to the
spin-orbit coupling with lifted degeneracy. Furthermore, the Mu$^0$ state exhibits transition to the Mu$^*$ state that corresponds to another Mu$^0$ state (exhibiting a diamagnetic response due to fast
spin/charge fluctuations) at temperatures above $\approx$10 K, before disappearing above $\approx$30 K. These findings suggest rapid diffusive motion of the $4f$ electrons and/or Mu (as well as H) at higher temperatures.
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All authors A. Koda, T. U. Ito, M. Hiraishi, H. Okabe, R. Kadono