Materials Science
Efficient perturbations for basin hopping in amorphous glasses
Coraline Du, Hye Sol Kim and Scott C. Warren
Efficient exploration of the complex potential-energy landscapes of amorphous materials is central to computational structure discovery and refinement. Conventional Monte Carlo, reverse Monte Carlo, and related methods typically sample configuration space through small, local trial moves and may require millions to tens of millions of moves to converge. Here, we evaluate larger, nonlocal perturbations followed by local geometry relaxation as an alternative sampling strategy. We develop and test four perturbation types using amorphous Al$_2$O$_3$ as a model system. Among them, moving an oxygen atom to change the coordination numbers of two aluminum atoms, allows access to low-energy configurations with substantially fewer trial moves than a conventional Monte Carlo trajectory. These results suggest that relaxation-assisted nonlocal moves could reduce trapping in local minima and improve sampling in structure-search and reverse Monte Carlo workflows.
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Materials Science
First-Principles DFT Study of Ferroelectric-to-Antiferroelectric Phase Transitions in LiTaO$_3$ under Electric Boundary Conditions
Eva Greene and Shaohui Qiu
Ferroelectric and antiferroelectric phases of LiTaO$_3$ compete under different electric boundary conditions. First-principles density-functional calculations show that the high-
symmetry reference structure supports two relevant unstable $\Gamma$ modes: a polar $A_{2u}$ mode at $181i$ cm$^{-1}$ that condenses into the ferroelectric (FE) phase, and an antipolar $A_{2g}$ mode at $103i$ cm$^{-1}$ that condenses into the antiferroelectric (AFE) phase. Under short-
circuit conditions the FE phase is the global minimum, with a well depth of $\approx 144$ meV. Under open-
circuit conditions the FE phase is destabilized by the unscreened depolarization field and the AFE phase becomes the ground state, with a well depth of $\approx 19$ meV. A weakly unstable longitudinal-optic mode at $48.3i$ cm$^{-1}$ yields a well of only $\approx 0.24$ meV and is thermodynamically irrelevant. Mapping the free energy versus electric displacement $D$ locates a second-order FE$\leftrightarrow$AFE transition at $D_c=0.051$ C/m$^2$, lower than the corresponding $0.07$ C/m$^2$ in LiNbO$_3$ and therefore more accessible experimentally.
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Materials Science
LDA-1/2 for Molecular Systems: A Real-Space Finite-Element Benchmark on the GW100 Set
Dongming Li, Niamh Matthews, Qingchuan Sang et al. (+1 more)
The LDA-1/2 method provides an efficient correction to semilocal density functional theory for improving ionization energies and band gaps, yet its application to molecular systems has remained limited. In this work, we present an all-electron finite-element implementation of LDA-1/2 within the NESSIE electronic-structure framework and apply it to the GW100 molecular
benchmark set with systematically controllable numerical accuracy. The self-energy correction is constructed explicitly from neutral and half-ionized calculations for each molecule, avoiding the use of precomputed atomic correction potentials. The real-space finite-element formulation enables systematic convergence with respect to the discretization and provides a controlled assessment of LDA-1/2 performance. For the GW100 set, the present implementation yields a mean absolute error of 0.472 eV and a root-mean-square error of 0.645 eV relative to CCSD(T) reference ionization energies, substantially improving upon conventional LDA and the previously reported LAPW implementation of LDA-1/2, while achieving accuracy comparable to G0W0@PBE. Convergence tests show that third-order finite elements are sufficient to reach or approach chemical accuracy relative to higher-order calculations for the representative systems considered. The resulting corrected
Hamiltonian also improves several lower lying valence states relative to LDA, although the improvement becomes less systematic away from the HOMO. This work provides accurate LDA-1/2
benchmark data for molecular systems and establishes a rigorous finite-element foundation for future molecular GW calculations.
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All authors Dongming Li, Niamh Matthews, Qingchuan Sang, Eric Polizzi
Materials Science
Physics-informed learning for the inverse problem in resonant ultrasound spectroscopy
Alejandro Cubillos Muñoz, Manuela Rivas and Julian Rincon
Inferring elastic constants from resonant ultrasound spectra is a nonlinear and typically overdetermined inverse problem based on finite spectral data. We formulate the Rayleigh-Ritz inverse problem as a constrained inverse-isospectral problem on the set of physically admissible elasticity tensors. This induces effective low-dimensional variables for the inverse map on the admissible elasticity
manifold: length and elastic scales, aspect-ratio coordinates, scale-free spectral features, and stability-respecting elastic ratios. We use these variables to construct a physics-informed learning pipeline in which a regression model acts only on reduced spectral and
geometric features, while scale recovery and final elastic-constant reconstruction are imposed analytically. For the full cubic
benchmark, the reconstructed constants have MAE values of $20.37(35.15)$, $24.30(41.33)$, and $2.13(3.66)~\mathrm{GPa}$ for $C_{11}$, $C_{12}$, and $C_{44}$. In the fixed-geometry
benchmark, the corresponding cubic MAPE values are $4.14(3.87)\%$, $8.31(8.50)\%$, and $2.44(2.86)\%$, while the isotropic values are $4.0(3.6)\%$ and $0.4(0.3)\%$ for the bulk and shear moduli. The inverse problem then becomes a constrained regression problem in variables adapted to the geometry, scaling,
crystal symmetry, and thermodynamic stability of Hookean elasticity.
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Materials Science
Atomistic Indicators of the Ductile-to-Brittle Transition in Polycrystalline Tungsten: Temperature and Rhenium Effects on Crack-Tip Plasticity
Divyesh Mistry and Avik Mahata
The fracture response of body-centered-cubic tungsten is governed by competition between crack-tip instability and dislocation-mediated plastic accommodation. Molecular dynamics (MD) simulations are used to examine edge-cracked polycrystalline W and W-Re under displacement-controlled Mode-I tension from 300-1800 K at a strain rate of 5 x 10^8 s^-1. Heating pure W reduces the instability stress, effective specimen stiffness, and pre-instability volumetric work density, while the instability strain remains comparatively scattered. A normalized work-loss metric derived from the pre-instability work gives a broad sigmoid crossover marker, T*_MD ~ 870 K, characteristic of the simulated geometry and high-rate loading conditions. Among the available W-Re compositions, W-10Re shows greater pre-instability deformation and work accumulation than pure W across most temperatures, while the maximum-stress response remains strongly temperature- and composition-dependent. Changes in retained dislocation character and near-tip activity indicate that Re modifies the crack-tip plastic-accommodation pathway rather than producing a simple strength increase. Common-state analysis further shows that Re alters the retained 1/2<111> line character and the temporal distribution of near-tip dislocation activity without uniformly increasing the local dislocation population. These coupled mechanical and defect-structure changes provide atomistic indicators of a high-rate ductile-to-brittle transition (DBT), but not a direct prediction of experimental DBTT. A separate OpenDiS/pydis calculation demonstrates source-like bow-out and heterogeneous dislocation-network development in crack-free polycrystalline W, providing mesoscale context without implying direct quantitative MD-DDD coupling.
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Materials Science
Compiling Chemical Knowledge into Executable Descriptors for Materials Prediction
Jaehwan Choi, Kunik Jang, Seongmin Kim et al. (+5 more)
Materials prediction depends critically on how scientific knowledge is represented, yet many governing considerations exist only as natural-
language heuristics that conventional learners cannot use. We introduce CRISP, a large
language model-assisted framework that treats representation construction as a rule-space exploration and compilation problem: it repeatedly samples target-relevant chemical rules without access to structures, labels or data splits, consolidates related concepts, and compiles each into an executable scalar descriptor supplied to a conventional learner. For positive-unlabeled inorganic-
crystal synthesizability, CRISP outperformed expert-curated and generic structural representations under a shared learner and surpassed purpose-built synthesizability models, with its advantage most pronounced under structural-size and chemical-family shifts. Infrequently generated rules contributed complementary predictive information, showing that generation frequency does not determine utility. The same workflow yielded competitive representations for formation energy and ionic conductivity while revealing task-dependent limits for shear modulus, establishing a
dataset-blind, auditable route from broad chemical knowledge to transferable computational representations.
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All authors Jaehwan Choi, Kunik Jang, Seongmin Kim, Shuan Chen, Kyungju Nam, Seung Hyo Noh, Donghwi Kim, Yousung Jung
Materials Science
Ab initio Modeling of MoS2/Oxide Device Interfaces with Machine Learned Electronic Structures
Manasa Kaniselvan, Mauro Dossena, Denghui Lu et al. (+4 more)
We introduce a new ab initio approach to simulate
semiconductor devices that integrates scalable machine-learned (ML) electronic structure models with an advanced
quantum transport (QT) solver. The developed framework enables 10,000X speedups over density functional theory to produce the
Hamiltonian matrix of devices made of >20,000 atoms, while offering high prediction accuracy. We use its unique features to investigate MoS2/oxide samples and single-layer MoS2 field-effect transistors, where the surrounding oxide layers, here, HfO2 or Al2O3, are explicitly included into the QT domain. In particular, we reveal that the presence of undercoordinated metal atoms (Hf or Al) close to the
semiconductor-oxide interface significantly affects the magnitude of the electronic current and its propagation through MoS2.
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All authors Manasa Kaniselvan, Mauro Dossena, Denghui Lu, Alexander Maeder, Nicolas Vetsch, Alexandros Nikolaos Ziogas, Mathieu Luisier
Materials Science
Exact branch-transfer criterion for common-mode Thomson heat cancellation in thermoelectric couples
Peng Kang, Da Wan, Shulin Bai et al. (+7 more)
Thermoelectric p- and n-type legs are commonly paired by matching their Seebeck magnitudes, although a cooler responds to heat transported through its complete electrical and thermal network. We decompose the leg coefficients into differential thermopower $\alpha=S_p-S_n$ and common thermopower $M=(S_p+S_n)/2$. In a connected steady-state scalar thermoelectric network, a temperature-independent co-shift applied to every electrically active segment is an exact terminal null. A temperature-dependent perturbation of the legs relative to fixed leads is instead physical. At fixed current and shared isothermal endpoints, its first-order cold-port response is the action of $\Gamma_m=T\,dm/dT$ on the difference between the p- and n-branch oriented collection measures. We prove that every continuous $\Gamma_m$ cancels if and only if these measures are equal. In the constant-property, linear-common-mode limit, matching $R_i/K_i^{\rm leg}$ is sufficient and does not require identical legs. One- and two-dimensional calculations confirm the analytic reductions within their stated domains. For split thermal pads, the analysis gives the exact array law $\Delta Q_{c,\Sigma}=\sum_j C_jI_j\Delta T_{c,j}$ and, for series elements with isothermal hot pairs, $I\Delta V_\Sigma=-\Delta Q_{c,\Sigma}$. A representative seven-pair model gives corresponding increments of 7.87 mW and $-2.80$ mV. Branch transfer and endpoint
topology therefore provide distinct material-pairing and device-test criteria for common-mode Thomson heat.
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All authors Peng Kang, Da Wan, Shulin Bai, Wei Yin, Peng Wang, Chenglong Wen, Zhen Li, Yu Liu, Lei Zheng, Li-Dong Zhao
Materials Science · Cross-listed from cond-mat.mes-hall
Band's Geometry Origin of Quantum Spin Transport Phenomena
Elena Derunova and Mazhar N. Ali
We develop a
geometric description of
spin-dependent transport based on the local
geometric structure of electronic bands and the Fermi surfaces. For quasi-two-dimensional systems, we show that
hyperbolic regions of constant-energy surfaces generate a geometrical contribution to the Fermi velocity that couples naturally to electron
spin and produces a
spin-current response. We further show that, in the presence of time-reversal
symmetry, the
algebra of
spin operators can be related to the exterior
algebra of the band's tangent space, providing an additional
geometric interpretation of
spin in momentum space. This framework motivates a symplectic description of
spin-separated transport on Fermi surfaces and its extension to three-dimensional band
manifolds through contact geometry. Our results establish a direct connection between Fermi-surface geometry and intrinsic
spin transport.
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Materials Science · Cross-listed from cond-mat.mes-hall
Scalable, Simple, and Versatile Encapsulation of 2D Materials and Devices
Gabriel Natale, Uma Chirkova, Flávio Henriques Feres et al. (+16 more)
Air-sensitive 2D materials present a fundamental challenge for device integration. Encapsulation is often required to preserve intrinsic properties, yet conventional protection strategies often fail for thicker layers and complicate fabrication. Here, we demonstrate that electron-beam (e-beam) evaporated aluminum oxide ($\mathrm{AlO}_x$) serves as both an effective encapsulation layer and a platform for direct device fabrication. Unlike transfer-based approaches, this scalable method is compatible with thicker flakes and full device or wafer coverage. It requires no stacking procedures and enables contacts without post-encapsulation etching. Using rare-earth tritellurides ($\mathrm{RTe}_3$, R = La, Er), semimetallic $\mathrm{WTe}_2$, and superconducting $\mathrm{FeTe}_x\mathrm{Se}_{1-x}$, we show that $\mathrm{AlO}_x$ suppresses oxidation and preserves intrinsic optical and electronic properties. We establish substrate-dependent optimization of encapsulation across a range of flake thicknesses, demonstrate that ultrathin $\mathrm{AlO}_x$ preserves $\mathrm{WTe}_2$'s plasmonic response and maintains superconducting performance in $\mathrm{FeTe}_x\mathrm{Se}_{1-x}$. Thus we overcome the longstanding tradeoff between encapsulation and straightforward device fabrication in fragile
quantum materials.
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All authors Gabriel Natale, Uma Chirkova, Flávio Henriques Feres, Ran Jing, Michael Geiwitz, Wenyao Liu, Emma Low, Josh Leeman, Kyung-Mo Kim, Leslie M. Schoop, Mohamed Shehabeldin, Qiong Ma, Michael A. Susner, Pijush Bhattacharya, Genda Gu, Katherine Lee, James Hone, Mengkun Liu, Kenneth S. Burch
Materials Science
Temperature dependence of the charge density from first principles: application to the (222) forbidden reflection in silicon
Jean Paul Nery, Raveena Gupta, Olle Hellman et al. (+2 more)
Forbidden reflections (FRs) in X-ray diffraction have inherently weak intensity and have long been studied, in particular in
semiconductors like silicon. They serve as sensitive probes of
symmetry breaking, local strain, impurities, and weak charge redistribution. Despite extensive experimental work, the theory of their temperature dependence has typically relied on simplified models. While atomic Debye-Waller factors work well on allowed reflections, their applicability to the valence charge between atoms, which determines the intensity of FRs such as Si (222), is questionable, and previous agreement between theory and experiment relied on ad-hoc Debye-Waller corrections. We compute the temperature-dependent valence charge density $\rho(\mathbf{r},T)$ of silicon from first principles, using two methods: (i) perturbation theory, and (ii) averaging over thermally distorted supercells in a non-perturbative approach. The perturbative expression for the charge density is far more demanding than that for electronic energies, since it depends on the wavefunctions themselves and requires an explicit sum over unoccupied bands. We use an acoustic sum rule to express the second derivatives of the potential in terms of first derivatives, making the expression tractable within existing frameworks. The (222) FR then follows directly from the
Fourier transform of $\rho(\mathbf{r},T)$, with no ad-hoc factors. Both methods give similar results, in reasonable agreement with experiment, with thermal expansion noticeably affecting the temperature dependence. The charge density answers a question the measured intensities could not settle: how the valence charge actually redistributes with temperature. Relative to the rigid model, we find more charge in the bonds and less in the core regions, a redistribution that shows up in the intensity as a somewhat weaker temperature dependence of the (222) FR.
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All authors Jean Paul Nery, Raveena Gupta, Olle Hellman, Philip B. Allen, Matthieu J. Verstraete
Materials Science
Coupled anisotropic weak topological states and Floquet mixed-parity altermagnetism in two-dimensional Su-Schrieffer-Heeger models
Kunyuan Feng, Xibin Liu, Chenchen Liu et al. (+5 more)
Su-Schrieffer-Heeger (SSH) topological systems and altermagnetic (AM) states are two important research areas in condensed matter physics. Realizing the coupled states between the SSH
lattices and AM phanse in a single syetem remains challenging. However, the Floquet engineering change it. Our work constructs five two-dimensional-(2D-) SSH models to describe the coupled phases of SSH weak topological state and AM order by tight-binding (TB) method. The
evolution of band structures,
spin-splitting, and topological phase transitions under the circularly polarized light (CPL) and relative atomic displacement (RAD) in 2D SSH
lattices were systematically investigated. The results reveal that the inequality of hopping parameters (t1 and t2) serves as the fundamental origin of SSH topological states and AM order. For the 2D nonmagnetic state, anisotropic weak topological states with Zak phase governed edge states are realized by unit
cell selection, similar to the conventional 1D SSH model. The collinear antiferromagnetic state preserves the
spin-degenerate band structure and intrinsic weak topological properties. Furthermore, the Floquet engineering introduces the AM phase of odd-parity p-wave while the RAD introduces the AM phase of even-parity d-wave. By combining the two effects, the mixed-parity (non-odd/non-even parity) AM phase could be realized, achieving the simultaneous control of the light field of
spin-splitting and topological edge states. The physical mechanisms of Floquet engineering and RAD for the 2D rectangular SSH
lattice are also from the inequality of t1 and t2, which can be not only fully understand by the TB methods, but also in good agreement with the first-principle calculations of 2D carbon-based materials. This work establishes an effective theoretical platform for coupling anisotropic SSH weak topological states and AM orders with multi-parities in 2D systems.
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All authors Kunyuan Feng, Xibin Liu, Chenchen Liu, Siyuan Liu, Lixiu Guan, Xiaobiao Liu, François M. Peeters, Linyang Li
Materials Science
Grain Boundary Phase Transitions Enable Diffusionless Climb of Disconnections
Md Sharier Nazim, Giacomo Po and Nikhil Chandra Admal
Dislocation-grain boundary (GB) interactions govern the mechanical response of polycrystalline materials by controlling dislocation absorption, transmission, and interfacial plasticity. While disconnection climb is conventionally understood to require the absorption or emission of point defects supplied through long range bulk
diffusion, GBs possess intrinsic configurational degrees of freedom associated with their atomic structure, or microstate, that may provide an alternative mechanism. Here, using bicrystallography and molecular dynamics simulations, we investigate the interaction of shear dislocation loops with the [1 1 0](-5 5 14) symmetric tilt grain boundary in Al. We show that dislocation absorption generates a mobile extrinsic disconnection with a nonzero climb component that propagates conservatively along the interface without long-range bulk point-defect transport. Its motion is accompanied by a localized GB phase transformation mediated by cooperative atomic rearrangements within the GB core, producing successive metastable GB microstates. These findings establish a direct coupling between
lattice dislocations and GB phase
evolution and reveal a conservative mechanism for disconnection climb fundamentally distinct from conventional vacancy-mediated climb.
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Materials Science
3D Cloud Component Analysis of Atomic Structures
Pai Li
We present a method for decomposing atomic structures into physically meaningful components by converting discrete atomic coordinates into continuous three-dimensional density fields. Each element is represented by a Gaussian-smeared density map with values ranging from 0 to 1, computed efficiently through a bin-then-blur approach with periodic boundary conditions. The sum of all element densities, truncated at unity, defines the material region; its complement defines the
vacuum. Every voxel is first assigned a chemical formula from the set of elements present above a threshold; the resulting formula map is then cleaned so that only regions with a genuine bulk interior-measured by the Euclidean distance to their own boundary-survive as components. Thin surface terminations (e.g., a Ga monolayer on GaAs) and one-to-two-voxel boundary layers between two
crystals are absorbed by the neighboring stable region, so the decomposition contains exactly the bulk-like chemical-formula components and the
vacuum, with no surface or interface components. For each component we determine the
crystal phase with a neural prototype classifier: one phase if the trusted interior atoms vote unanimously, two phases (e.g., crystalline and amorphous Si) if they split into two confident groups, in which case the component is divided into two. Interfaces and surfaces are then derived as boundaries-material-material and material-
vacuum-and every atom is labeled bulk, surface, interface, or vertex, with vertex reserved for
geometric corners of a component. Inside crystalline components, inner defects are detected from coordination-number and local-density deviations. We demonstrate the approach on Si/GaAs and Si/SiO2 heterojunctions, crystalline/amorphous silicon junctions, vacancy-containing
crystals, and bulk
crystals.
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Materials Science
Benchmarking of Fast and Interpretable UF Machine Learning Potentials
Pawan Prakash, Sam Dong and Richard G. Hennig
Machine learning interatomic potentials (MLIPs) have emerged as a powerful alternative to density functional theory (DFT) for molecular dynamics simulations, offering near-DFT accuracy at a fraction of the computational cost. However, many state-of-the-art MLIPs remain computationally demanding and act as black boxes, limiting physical interpretability. In this work, we evaluate the ultra-fast force field (UF$^3$) potential, which employs linear regression with cubic B-spline basis to represent effective two- and three-body interactions. We show that UF$^3$ displays accuracy comparable to established models such as GAP, MTP, NNP (Behler Parrinello), and qSNAP MLIPs. We further investigate the transferability of UF$^3$ by computing melting points for six elemental systems with potentials fitted without any solid-
liquid interface configurations or explicit thermodynamic information about melting. The model reproduces experimental melting points within $\sim$6% for simple metals (Ni, Cu, Li), but substantially underestimates them for Mo and Si and fails to yield a stable potential for Ge, reflecting the limitations of a fixed expansion truncated at the three-body term for systems with strong angular or covalent bonding. We further illustrate how UF$^3$'s spline-based formulation allows direct visualization of the learned interactions, enabling identification of unphysical behavior that black-box approaches often obscure.
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Materials Science
Grain-Boundary Premelting in High-Entropy Transition Metal Carbides
Marium M. Mou, Caleb Schenck, Samuel E. Daigle et al. (+4 more)
Grain-boundary segregation and thermally induced interfacial disordering were investigated in four high-
entropy transition metal carbides using Monte Carlo (MC) sampling and molecular dynamics (MD) with the universal MACE-OMAT-0 machine-learning interatomic potential. MC sampling segregated the group-VI element (Cr, Mo, or W) and Zr to grain boundaries, where the group-VI content reached approximately 45 at.%, consistent with STEM-EDS observations. During MD heating, the grain-boundary Lindemann index, a normalized measure of interatomic distance fluctuations, reached the
liquid-like threshold of $\delta=0.15$ near $1390^{\circ}\mathrm{C}$ for the Cr-containing carbides, $1660^{\circ}\mathrm{C}$ for Mo, and $1890^{\circ}\mathrm{C}$ for W, while the grain interiors remained below the threshold. A chemically random (Cr,Hf,Ta,Ti,Zr)C reference crossed about $60^{\circ}\mathrm{C}$ later and showed less boundary-localized disorder, highlighting the role of interfacial chemistry in premelting. Species-resolved displacements showed enhanced grain-boundary mobility, particularly for carbon. Overall, Cr-rich interfaces showed the earliest and most extensive premelting-like response, followed by Mo- and W-containing boundaries.
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All authors Marium M. Mou, Caleb Schenck, Samuel E. Daigle, William G. Fahrenholtz, Bharat Gwalani, Stefano Curtarolo, Donald W. Brenner
Materials Science
Crystal Structure Prototype Identification via Element-Mapped Rotation-Invariant Descriptors
Pai Li
We present a method for identifying
crystal structure prototypes from local atomic environments. A center atom and its neighbors within a distance-normalized cutoff are mapped to anonymous element types (A/B/C/D) by proximity, and a NEP-style descriptor-radial Chebyshev moments plus contracted spherical-harmonic (S-vector) invariants-is computed per type block. The descriptor is rotation-invariant by construction (MLFF-style contraction with analytic normalization constants), so no rotation augmentation is needed. A trainable block-diagonal projection compresses the 316-dimensional raw basis into a 168-dimensional learned descriptor fed to a three-layer MLP. The model classifies each atom into one of 271 AFLOW
crystal structure prototypes or the amorphous class (272 classes), reaching 99.38% accuracy on 538,190 per-atom samples. The full pipeline (descriptor extraction + inference) runs on a single CPU core at 3.9 s per 10,000 atoms, making it suitable for website deployment.
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Materials Science · Cross-listed from cond-mat.str-el
Multi-orbital physics in inverse Lieb lattice altermagnets
Mercè Roig, Jannik Gondolf, Andreas Kreisel et al. (+2 more)
The inverse Lieb
lattice has recently emerged as a promising platform for altermagnetism, with several materials with this structure proposed as $d$-wave altermagnetic candidates. Here, we develop a
symmetry-based microscopic
Hamiltonian for these materials that includes both sublattice and orbital degrees of freedom, going beyond the sublattice-only minimal models that have been extensively used to study such altermagnets. We apply these models to examine multi-orbital electron correlation physics in the vanadium oxychalcogenide family altermagnets, which contain dominant $xy$ and $xz/yz$ orbitals character at the Fermi level in the altermagnetic state. We demonstrate that $xy$ orbitals are crucial to stabilize the altermagnetic state observed within a single V$_2$O layer, and altermagnetic order in the $xz/yz$ orbitals is induced through Hund's coupling. Additionally, we show that these multi-orbital models reveal topological regimes in which topological edge states are naturally orbital selective.
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All authors Mercè Roig, Jannik Gondolf, Andreas Kreisel, Brian M. Andersen, Daniel F. Agterberg
Materials Science · Cross-listed from cond-mat.mes-hall
Terahertz anomalous Hall effect in magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$
Ashutosh Singh, Hongjing Xu, Xielin Wang et al. (+6 more)
Time-reversal-
symmetry-broken Weyl semimetals are known to have at least two nodes in their electronic band structure, separated in momentum space and acting as sources and sinks of Berry
curvature. This gives rise to a transverse Hall conductivity, known as the anomalous Hall effect (AHE), which, in the simplest two-node picture, is proportional to the momentum-space separation between the nodes in the zero frequency limit. In the recently discovered Weyl semimetal $\mathrm{Co_3Sn_2S_2}$, a giant AHE has been observed. However, experimental investigations in the low-energy regime, which directly probe quasiparticle excitations near the Weyl nodes, remain limited. Here, we present a systematic study of the intrinsic low-energy gyrotropic optical response of $\mathrm{Co_3Sn_2S_2}$ using terahertz spectroscopy combined with semianalytical calculations based on a physically intuitive effective model. Our results provide a robust and transparent explanation of the observed magnetooptical phenomena in terms of intrinsic gyrotropy arising from momentum-space separation of the Weyl nodes. Furthermore, quantitative comparison between experiment and theory places stringent constraints on the material parameters.
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All authors Ashutosh Singh, Hongjing Xu, Xielin Wang, Kohei Fujiwara, Atsushi Tsukazaki, Shengxi Huang, Andrey Baydin, Junichiro Kono, Alexey Belyanin
Materials Science · Cross-listed from physics.chem-ph
ElemCo.jl: A Julia package for electron-correlation methods
Daniel Kats, Charlotte Rickert, Thomas Schraivogel et al. (+3 more)
We present ElemCo.jl, an open-source Julia package for molecular electronic structure and properties calculations with a particular emphasis on Coupled Cluster and Distinguishable Cluster methods. The package provides a high-level, macro-based user interface which makes routine calculations accessible to users with no prior Julia experience. A newly developed visualizer, JLmol, assists in the graphical preparation of ElemCo.jl input files and displays results such as molecular orbitals. ElemCo.jl offers restricted closed-shell and unrestricted variants of state-of-the-art electron-correlation methods such as FCI, MP2, CCSD(T) as well as EOM-CCSD and the DC methods DCSD and DC-CCSDT. In addition to traditional approaches, ElemCo.jl provides recently developed methods that are currently unique to the package. These include tensor-decomposed implementations of DCSD and DC-CCSDT (SVD-DCSD and SVD-DC-CCSDT) as well as two-determinant and fixed-reference CC and DC methods. For excited-state calculations, ElemCo.jl also offers EOM-DCSD, which is benchmarked in this work against CC3 on the QUEST3
benchmark set, alongside EOM-CCSD. Furthermore, both ground and excited states, including those of multireference character, can be treated using CIPHI - an efficient selected Configuration Interaction (CI) approach employing a CIPSI/Heat-Bath-CI-based
algorithm. Users can directly invoke internal functions from the input file, enabling them to test and compose new methods without the need to modify ElemCo.jl's source code. Also, ElemCo.jl can be readily interfaced with external
quantum chemistry codes through the Fcidump format, for example as the high-level solver for transcorrelated
Hamiltonians, periodic embedded fragments, etc. We provide a detailed overview of ElemCo.jl's methodological repertoire and discuss its technical details and implementation, performance, interfaces, and usage.
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All authors Daniel Kats, Charlotte Rickert, Thomas Schraivogel, Kristoffer Simula, Denis Usvyat, Fangcheng Wu
Materials Science
Data-efficient crack quantification in lithium-ion cathodes using foundation model transfer
Thorsten Tegetmeyer-Kleine, Thomas Schmitt, Phillip Aquino et al. (+3 more)
Battery lifetime is central to sustainable electrification, yet the particle cracking that drives lithium-ion cathode aging is hard to measure: quantitative microscopy of this degradation is bottlenecked by annotation, because each destructive electron-microscopy cross-section spans hundreds of megapixels and pixel-level expert labelling requires hours per image. We show that a frozen self-supervised
vision-
transformer encoder, combined with a lightweight trainable decoder and iterative model-assisted annotation, turns this sparse labelling budget into population-scale degradation measurements. Applied to three 120-megapixel NMC cathode cross-sections representing initial, cycled-aged and calendar-aged states, the framework distinguishes intragranular cracks from early- and late-stage intergranular cracks and yields per-particle distributions of crack width, tortuosity and area fraction. Late intergranular crack coverage reaches 4.6% in the cycled sample versus 0.5% in the initial and calendar-aged samples, forming more tortuous, higher-coverage networks, consistent with degradation from repeated electrochemical cycling rather than elevated-temperature storage alone. A single destructive image yields the population-level statistics needed for lifetime-extending design, aging assessment and second-life decisions.
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All authors Thorsten Tegetmeyer-Kleine, Thomas Schmitt, Phillip Aquino, Christiane Rahe, Dirk Uwe Sauer, Weihan Li
Materials Science · Cross-listed from physics.geo-ph
Quantifying the effects of nickel on Earth's inner-core nucleation
Jiahui Zhai, Liangrui Wei, Chen Gao et al. (+1 more)
The formation of Earth's solid inner core marks a major transition in the thermal and chemical
evolution of the deep Earth, yet its origin remains paradoxical, as initial nucleation appears to require unrealistically large undercooling in the outer core. Here, we use atomistic simulations to quantify how Ni affects this process under inner-core conditions. While Fe-Ni
alloys preserve strong thermodynamic competition between the hcp and bcc phases, the bcc phase consistently forms smaller critical
nuclei and has lower nucleation barriers than hcp. Increasing Ni content in the melts further lowers the nucleation barrier and shortens the nucleation waiting time. Local chemical fluctuations also strongly affect the macroscopic nucleation rate. Combining these effects, bcc nucleation in Fe80Ni20 reaches about 250 K of undercooling, approaching geophysical constraints. We demonstrate that Ni enrichment, bcc nucleation, and chemical heterogeneity substantially narrow the inner-core nucleation paradox.
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All authors Jiahui Zhai, Liangrui Wei, Chen Gao, Yang Sun
Materials Science
Emergent Skyrmion Hall Effect in $d$-wave Altermagnets at Finite Temperature
Tingting Liu, Bingyu Sun, Fengyue Zhu et al. (+4 more)
Altermagnets combine compensated
magnetic order with unconventional
symmetry-dependent responses, offering a promising platform for spintronic applications. Here, we show that a voltage-controlled
magnetic-anisotropy gradient drives altermagnetic (ATM) skyrmions in a nearly rectilinear, Hall-free manner in the absence of thermal fluctuations, owing to their strongly compensated gyrotropic response. Thermal
magnons qualitatively modify this behavior by increasing the longitudinal drag through
magnon–skyrmion scattering and generating a transverse reaction force through handedness-dependent skew scattering. Owing to the anisotropic altermagnetic
magnon band structure, the relative transport weights of the two
magnon handednesses are interchanged between propagation along the $x$ and $y$ directions, resulting in transverse skyrmion drifts of opposite sign. By contrast, along the high-
symmetry direction, the two
magnon handednesses remain degenerate and their transverse contributions cancel, preserving Hall-free motion even at finite temperature. We thus uncover a thermally emergent anisotropic skyrmion Hall effect whose direction-dependent magnitude and sign originate from the intrinsic
symmetry-dependent
magnon spectrum, making it a generic finite-temperature dynamical feature of ATM skyrmions. Our results establish a low-power route toward electrically controlled and thermally tunable ATM skyrmion transport.
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All authors Tingting Liu, Bingyu Sun, Fengyue Zhu, Zhihui Zhang, Peiyu Zhang, Yang Liu, Minghui Qin
Materials Science
Laser induced ultrafast Co 3d and Ho 4f spin dynamics in CoHo ferrimagnetic alloys
Deeksha Gupta, Boonthum Kunyangyuen, Matthias Riepp et al. (+8 more)
The transition metal (TM) / rare-earth (RE)
alloys have received renewed interest lately as model systems to decipher the origin of all-optical helicity-independent switching (AO-HIS) by femtosecond
laser pulses. Recently, a distinct single-pulse magnetization reversal mechanism, based on domain-wall motion and coalescence, has been reported in CoDy and CoHo
alloys, as well as in Co/Gd ultrathin bilayers. It has been claimed that this specific toggle switching is achieved when the Co sublattice is fully demagnetized and the characteristic demagnetization times {\tau}RE of the RE (Gd, Dy or Ho) sublattices is longer than that of the Co and the angular momentum transferred to Co is reduced. Element- and time-resolved X-ray spectroscopy studies of CoDy
alloys have reported characteristic demagnetization times of {\tau}Co = 0.2 ps and {\tau}Dy = 0.6 ps at room temperature. Similarly, Ho is expected to exhibit a slower response, but its ultrafast 4f
spin dynamics remain experimentally unexplored. Here, we report on element- and time-resolved investigations of femtosecond
laser induced ultrafast dynamics of the Co 3d and Ho 4f
spins in ferrimagnetic Co_{80}Ho_{20}
alloys to verify this prediction. We observed characteristic demagnetization times {\tau}Co = 0.22 +/- 0.01 ps and {\tau}Ho = 0.87 +/- 0.15 ps at room temperature. These results show that Ho demagnetizes substantially more slowly than Co in Co_{80}Ho_{20}, supporting the proposed condition for domain-wall-mediated all-optical toggle switching
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All authors Deeksha Gupta, Boonthum Kunyangyuen, Matthias Riepp, Karsten Holldack, Radu-Marius Abrudan, Torsten Kachel, Niko Pontius, Christian Schüßler-Langeheine, Mircea Vomir, Michel Hehn, Nicolas Bergeard
Materials Science
THz-induced phonomagnetism in diamagnetic quantum paraelectric KTaO$_3$
C. Kadlec, F. Kadlec, D. Repček et al. (+13 more)
The current efforts striving to develop new ways of data manipulation are aimed at ultrafast control of magnetization in
magnetic materials, as well as at inducing
magnetic moments in diamagnetics. We demonstrate that in the diamagnetic
quantum paraelectric KTaO$_3$, the electric field of circularly polarized THz pulses with an amplitude of $\sim 300\,$kV/cm induces a transient
magnetic-like response by resonantly exciting its degenerate soft polar
phonon. This
phonon-mediated response was measured using the THz pump—optical probe technique via the time-resolved magneto-optic Faraday effect. Our detection scheme was set up to cancel out the major part of the electro-optic Kerr effect which also usually significantly contributes to the transient response. The Kerr-effect-related signal was further suppressed by subtracting the experimental data related to oppositely circularly polarized THz radiation. Thus, we were able to unambiguously identify a temperature-dependent
magnetic-like behavior of the KTaO$_3$
crystal manifested by the extracted Faraday rotation. We developed a theoretical model describing well quantitatively the measured curves of the transient Faraday effect signal. However, their amplitudes exhibit an unexpected temperature dependence, which might be a key to a deeper understanding of the observed phonomagnetic effect.
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All authors C. Kadlec, F. Kadlec, D. Repček, P. Kužel, M. Basini, J.-C. Deinert, S. Kovalev, T. Tadano, M. Udina, I. Ilyakov, T.V.A.G. de Oliveira, A. Ponomaryov, A. Arshad, A. Maia, S. Bonetti, S. Kamba
Materials Science · Cross-listed from physics.flu-dyn
High-resolution in situ analysis of biomass pyrolysis by combining quantitative synchrotron $\mu$CT and 3D particle-resolved simulations
Emeric Boigné, Mohamed M. Ahmed, Collin Foster et al. (+7 more)
Understanding the coupling between transport, chemical kinetics, and structural response within solid fuel combustion requires in situ measurements at high spatial resolution. To examine the dynamics of biomass pyrolysis, we optimize synchrotron X-ray micro-computed
tomography ($\mu$CT), and conduct 3D particle-resolved simulations. A micro-focused heating
cell with controlled heating and flow rate is employed, achieving temperatures of up to 1240 K and 3D imaging at 3.24 $\mu$m spatial and sub-minute temporal resolutions. The pyrolysis of three biomass materials at sample heating rates of 10-14 K/min are examined. The $\mu$CT measurements capture pore deformation, cracking, anisotropic shrinkage, and provide simultaneous thermogravimetric and thermovolumetric analyses to examine specific secondary pyrolysis pathways. Complementary 3D simulations considering detailed kinetics and structural response reproduce the key trends observed, and identify deficiencies in capturing simultaneous mass and volume losses during pyrolysis.
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All authors Emeric Boigné, Mohamed M. Ahmed, Collin Foster, Edna R. Toro, Dilworth Y. Parkinson, Alastair A. MacDowell, Harold S. Barnard, Francesco Panerai, Chiara Saggese, Matthias Ihme
Materials Science
Intrinsic anomalous Hall response in the bilayer kagome ferromagnet Co$_3$Sn
Yuqi Qin, Soumya Sankar, Xingkai Cheng et al. (+4 more)
Transition-metal kagome magnets provide a rich platform for investigating the interplay between layer stacking,
magnetic order, and band
topology. Here, we report the molecular beam epitaxy and experimental investigation of high-quality thin films of the kagome metal Co$_3$Sn, which has not been synthesized in bulk form yet. Structural and chemical analyses confirm a hexagonal
lattice structure ($P6_3/mmc$) composed of direct A-B stacked Co$_3$Sn kagome bilayers. Magnetometry reveals robust easy-plane ferromagnetism with a Curie temperature exceeding $300\,\text{K}$. Magneto-transport measurements demonstrate metallic behavior (carrier density $n\approx5.01\times10^{22}\,\text{cm}^{-3}$) alongside a temperature-independent anomalous Hall conductivity of $\sigma_{\rm AHE}\approx90\,\Omega^{-1}\cdot{\rm cm}^{-1}$, extending from $2\,\text{K}$ up to room temperature. Results from first-principles density functional theory calculations attribute this anomalous Hall response to intrinsic Berry
curvature hotspots near the Fermi level in the
spin-split band structure. Our results establish Co$_3$Sn as a room-temperature kagome ferromagnet and highlight the impact of the layer stacking sequence on the material properties of kagome metals from the CoSn family.
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All authors Yuqi Qin, Soumya Sankar, Xingkai Cheng, Yifan Jiang, Shiming Lei, Junwei Liu, Berthold Jäck
Materials Science
Atomic-scale composition of the ternary III-V semiconductor (Al,Ga)Sb visualized by cross-sectional scanning tunneling microscopy
Hitesh Kumar, Vladimir Kaganer, Zijin Lei et al. (+3 more)
Cross-sectional scanning tunneling microscopy at 5 K is used to investigate cation mixing in (Al,Ga)Sb layers grown by molecular beam epitaxy, via direct atom counting at the (1-10) and (110) cleavage planes. Electronic contrast between Al and Ga surface cations enables statistical analysis of the metal sublattice along the non-equivalent <110> directions within the zincblende (001) surface and along the [001] growth direction. The cation distribution is found to be random both along the growth direction and within the growth plane, with no evidence of long-range order or anisotropic growth kinetics; notably, the mean numbers of consecutive cations of the same type along the two in-plane directions are equal, possibly due to statistical averaging over randomly distributed subsurface cations. The results are compatible with either strain-mediated interactions during cation incorporation at the growth front or ideal, uncorrelated cation mixing. Overall, the examined (Al,Ga)Sb
alloy shows an exceptionally high degree of atomic-level homogeneity.
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All authors Hitesh Kumar, Vladimir Kaganer, Zijin Lei, Rüdiger Schott, Werner Wegscheider, Stefan Fölsch
Materials Science
Topology-Controlled Phonon Dielectric Response Beyond Density Scaling in Metal-Organic Frameworks
Debayan Mondal, Jiahao Ye, Lorenzo Donà et al. (+1 more)
Effective-medium theory treats material porosity as passive dilution. Using ab initio density functional theory and high-resolution synchrotron terahertz (THz) spectroscopy on isochemical zeolitic-imidazolate frameworks, we show that while the electronic permittivity obeys Clausius-Mossotti density scaling, the
phonon contribution violates the conventional density scaling rules. Identical Born charges rule out the role of local chemistry. Instead, the framework connectivity localizes the THz response, where the coherency of
phonon eigenvectors determines the mode-effective charges. Long-range architecture of framework
topology ubiquitous in metal-organic frameworks is therefore a dielectric degree of freedom beyond the density scaling of conventional solids.
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All authors Debayan Mondal, Jiahao Ye, Lorenzo Donà, Jin-Chong Tan
Materials Science · Cross-listed from cond-mat.mes-hall
Hall effect in viscous flows of two-dimensional electrons in samples with edges of arbitrary roughness
A.V. Gert and P.S. Alekseev
In ultra-clean conductors, fast inter-particle collisions can lead to the formation of a viscous electron fluid and realization of the hydrodynamic transport regime. Here we develop a theory of hydrodynamic magnetotransport of two-dimensional (2D) electrons in samples with low densities of defects and edges of arbitrary roughness. Within our model the roughness is described by a single parameter with the dimension of speed in the boundary conditions on sample edges. The electron-fluid flow profiles in long samples, as well as the corresponding longitudinal and Hall resistances, are calculated. The contribution to the Hall resistance associated with the relaxation processes exhibits a saturation in the limit of high
magnetic field and a minimum as a function of the
magnetic field for sufficiently rough edges. The minimum disappears as the edge roughness decreases or the sample width and bulk scattering by defects increase. These properties of the Hall resistance can serve as the signs to identify the hydrodynamic regime of electron transport in experiments and can be used to determine its parameters, in particular, the degree of edge roughness.
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