Materials Science · Cross-listed from physics.chem-ph
Transcorrelated Random-Phase Approximation
Abdallah Ammar, Enzo Monino, Anthony Scemama et al. (+2 more)
We extend the random-phase approximation (RPA) to the non-Hermitian transcorrelated (TC)
Hamiltonian, which explicitly includes three-body interactions generated by a Jastrow correlation factor. We consider both the direct RPA (dRPA) and RPA with exchange (RPAx). We apply the resulting TC-dRPA and TC-RPAx methods to calculate ground-state correlation energies and vertical excitation energies for atoms (\ce{He} and \ce{Ne}) and small molecules (\ce{H2O}, \ce{NH3}, \ce{CH4}, and \ce{H2CO}). For ground-state correlation energies, the TC treatment substantially improves accuracy and accelerates basis set convergence, reducing errors by nearly an order of magnitude relative to conventional RPA calculations. By contrast, it yields only marginal improvements in vertical excitation energies. We attribute this limited effect to the ground-state optimization of the Jastrow factor, which does not adequately capture the distinct electronic character of excited states. These results establish TC-RPA as an accurate and computationally efficient approach to ground-state energetics, while highlighting the need for state-specific Jastrow optimization to achieve reliable descriptions of excited states.
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All authors Abdallah Ammar, Enzo Monino, Anthony Scemama, Emmanuel Giner, Pierre-François Loos
Materials Science
An End-to-End Differentiable Forward Model for High-Energy Diffraction Microscopy
Hemant Sharma, Nina Andrejevic, Simon Zhang et al. (+1 more)
High-Energy Diffraction Microscopy (HEDM) recovers crystallographic orientation, strain, and grain position from rotating-
crystal X-ray diffraction patterns. Existing forward models in far-field (FF), near-field (NF), and point-focused (pf) HEDM are not differentiable, which forecloses gradient-based joint parameter refinement, physics-informed regularisation, and
Bayesian uncertainty quantification. We present the first end-to-end differentiable HEDM forward model covering all three geometries, implemented in PyTorch with pixel-exact agreement against the established MIDAS reference simulators (162/162 FF, 2304/2304 NF including a non-zero detector-tilt sweep, and 1088/1096 pf-HEDM spots matched). Three demonstrations validate the framework: joint orientation-strain-position recovery in NF-HEDM at ~6 nm precision; round-trip refinement on a real 214-grain alpha-Ti FF-HEDM
dataset reaching 100% grain recovery from a 1.5 degree initial perturbation with residuals matching the production fit to 0.3%; and joint refinement of all per-detector geometry parameters and per-grain state on a synthetic four-panel FF-HEDM setup, recovering panel rotations about the beam axis to ~10 mu-rad and a global rotation-axis wedge to ~26 mu-rad. The framework is released as the open-source midas-diffract package (pip install midas-diffract).
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All authors Hemant Sharma, Nina Andrejevic, Simon Zhang, Mathew Cherukara
Materials Science
Ultrafast Nonthermal Lattice Destabilization and Suppression of Polar Optical Scattering in Electronically Excited $\alpha$-SiO$_2$ from First-Principles and Deep Neural Network Potential Modeling
Iyyappa Rajan Panneerselvam, Mark Yeung, Charlotte Palmer et al. (+2 more)
We present a multiscale first-principles-to-machine-learning approach to investigate ultrafast
lattice dynamics in electronically excited $\alpha$-SiO$_2$. Ab initio molecular dynamics (AIMD) based on electronic-temperature-dependent density functional theory (DFT) are used to train electronic-temperature-dependent deep neural network potentials (DNNPs). The use of DNNPs enables atomistic modeling at near-DFT accuracy of large $\alpha$-SiO$_2$
cells with thousands of atoms. In particular, DNNPs allowed us to obtain accurate
phonon band structures and molecular dynamics (MD) of $\alpha$-SiO$_2$ excited by a sudden increase in electronic temperature. With increasing electronic temperature, $T_e$, pronounced
lattice destabilization of $\alpha$-SiO$_2$ is found, as evidenced by violations of elastic stability criteria, substantial volumetric expansion, a sharp reduction of the bulk modulus, and progressive weakening of Si-O bonding due to antibonding-state occupation. From the electronic and
phonon band structures, we estimated the Frohlich coupling constant, which decreases as $T_e$ increases, suggesting a crossover to a nonpolar phase of $\alpha$-SiO$_2$ at elevated electronic temperature. This is corroborated by the Bader charge analysis. We also suggest that polar optical
phonon scattering should be strongly suppressed at $T_e > 2$ eV. From large-
cell DNNP-MD simulations, we show that a well-defined thermal
equilibrium, as defined by the Maxwell-Boltzmann distribution, is not achieved over the first few hundred femtoseconds. This behavior explains the non-monotonic equilibration of the kinetic temperature after a sudden rise of $T_e$. After $T_e$ is raised to 2.6 eV, Si and O atoms first equilibrate separately at two different temperatures, suggesting an atomic fluid phase, in agreement with recent experimental and theoretical findings.
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All authors Iyyappa Rajan Panneerselvam, Mark Yeung, Charlotte Palmer, Brendan Dromey, Lorenzo Stella
Materials Science
Giant Exfoliation Induced Magnetic Coercivity in Fe$_3$GaTe$_2$
Lingrui Mei, PeiYu Cai, Sang-Eon Lee et al. (+6 more)
Permanent magnets with strong anisotropy and high coercivity underpin modern information and energy technologies, yet rare-earth-free alternatives remain limited. Here, we show that thickness engineering via mechanical exfoliation induces hard
magnetic behavior in the van der Waals ferromagnet Fe$_3$GaTe$_2$. Bulk
crystals exhibit Curie temperatures above 350 K but negligible room-temperature coercivity. When thinned below 100 nm, the coercive field is dramatically enhanced, reaching nearly 1 T at room temperature for in-plane fields which is comparable to values of conventional hard magnets. Micromagnetic analysis reveals a crossover in magnetization reversal from domain-mediated processes in bulk samples to quasi-coherent rotation in thin flakes, driven by increased effective anisotropy and suppressed domain formation. This thickness-dependent transition enables tuning of
magnetic hardness without chemical modification. Combined with high saturation magnetization and robust room-temperature performance, Fe$_3$GaTe$_2$ emerges as a promising rare-earth-free material for spintronic applications. Its layered structure further allows integration into van der Waals
heterostructures, where large in-plane coercivity can stabilize
magnetic states against perturbations and interlayer coupling, offering potential for high-density nonvolatile
memory and domain-wall-based devices.
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All authors Lingrui Mei, PeiYu Cai, Sang-Eon Lee, Yue Li, Shyam Raj Karullithodi, Vadym Kulichenko, Charudatta Pathak, Elton J. G. Santos, Luis Balicas
Materials Science · Cross-listed from cond-mat.mes-hall
Engineering micro-disorder for macro-performance in magnetic nanoparticles
Jonathan Leliaert and Elizabeth M Jefremovas
Spin disorder, inherent to
magnetic nanoparticles, has traditionally been regarded as a detrimental feature, with materials-engineering efforts largely focused on producing ”perfect particles” containing as few defects as possible. Alongside this pursuit of perfection, however, an alternative framework has emerged in recent years that reframes intra-particle disorder as an ”ugly duckling” whose functional potential remains to be unlocked. In this Perspective, we review the emerging concept of disorder engineering in
magnetic nanoparticles, identify its current challenges, and outline promising future directions. From a theoretical standpoint, progress requires moving beyond the widely used macrospin approximation, which severely restricts the description of intra-particle degrees of freedom. Micromagnetic modelling, in contrast, treats magnetisation as a continuous vector field and thereby enables (i) the explicit representation of intra-particle degrees of freedom, linking microstructural features to internal magnetisation textures, and (ii) direct correspondence with polarized small-angle
neutron scattering, an experimental technique that provides quantitative access to ensemble-averaged
magnetic correlations on nanometre length scales. The field must now advance towards falsifiable and uncertainty-aware models with structurally motivated parameters and predictions that can be tested against independent experimental observables. The overarching goal is to establish quantitative relationships between particle structure, intra-particle magnetisation textures, and macroscopic functionality, thereby transforming
spin disorder from an elusive hidden variable into an engineerable design parameter.
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Materials Science
Open-Shell Molecules as Sensitive Probes of Spin-Orbit-Controlled Surface Electronic Structure
Solange Mariel Di Napoli, Alexei Nefedov, María Andrea Barral et al. (+5 more)
Open-shell molecules are highly sensitive probes of correlated oxide surfaces because their partially occupied frontier orbitals strongly amplify subtle changes in adsorbate-substrate hybridization. Combining infrared reflection-absorption spectroscopy with hybrid density functional theory including non-collinear magnetism and
spin-orbit coupling, we show that inclusion of
spin-orbit coupling is essential to reproduce the vibrational spectrum of NO adsorbed on UO$_2$(111) by suppressing an otherwise artificial overhybridization between the NO frontier orbitals and uranium 5f states. While
spin-orbit coupling determines the position of the N-O stretching and, dispersion-driven intermolecular interactions account for its asymmetric broadening at monolayer coverage. These results establish open-shell molecules as sensitive probes of
spin-orbit-controlled surface electronic structure and identify NO/UO$_2$(111) as a stringent
benchmark for electronic-structure methods describing open-shell molecule-surface interactions.
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All authors Solange Mariel Di Napoli, Alexei Nefedov, María Andrea Barral, Gustavo E. Murgida, Ana María Llois, Christof Wöll, M. Verónica Ganduglia-Pirovano, Verónica Laura Vildosola
Materials Science
Electrical Control over Volatile Mott Switching through Non-Volatile Memory Effects
Amihai Kronman, Gil Levi and Yoav Kalcheim
Vanadium Dioxide (VO2) and Vanadium Sesquioxide (V2O3) are Mott
insulators that undergo an
Insulator-to-Metal Transition (IMT) at ~340K and ~160K, respectively, manifested as an orders-of-magnitude reduction in their electrical resistance. These transitions provide the physical basis for their Volatile Resistive Switching (VRS) behavior, making them promising candidates for threshold-switching devices. Here, we show that the volatile switching in these materials can be strongly affected by non-volatile processes associated with the creation and annihilation of the conducting filament. These processes give rise to pronounced
memory effects in which the initial switching voltage substantially exceeds that of subsequent cycles. We identify two distinct mechanisms underlying this behavior in different thermal regimes. In the phase-coexistence regime, a
memory effect is observed in V2O3, arising from the spatial redistribution of metallic and insulating domains. Well below the hysteresis regime, an additional electroforming-like
memory effect is observed in both VO2 and V2O3 which is attributed to the formation and/or migration of defects under the influence of a high electric field and a current surge associated with the IMT-driven switching. Using a protective internal resistor and a multi-step writing protocol, this normally destructive process can be harnessed to tune the switching voltage and power over a wide temperature range. These results demonstrate a route toward controlled programming of switching parameters in IMT-based resistive switching devices.
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Materials Science · Cross-listed from cs.LG
Representations from Pretrained Machine-Learning Interatomic Potentials as Coarse Coordinates for Material Generation and Evaluation
Paul Hagemann, Katharina Ueltzen, Simon Müller et al. (+2 more)
Generative machine learning is increasingly used for inorganic
crystal structure generation. Most models and the corresponding evaluation approaches rely on simple forms of
crystal structure representation. In this paper, we showcase the power of atom-averaged features from pretrained Machine-Learning Interatomic Potentials (MLIPs), such as MACE, for such tasks. We first introduce a distance measure that assesses the output of material generative models by capturing both quality and novelty in a single distribution-based evaluation framework. In particular, we introduce the Coarse-Fine Transport Distance (CFTD) using two different featurizers, where the quality component is based on coarse MACE features. We showcase CFTD's versatility in capturing
crystal-structure quality while also detecting memorization, and compare it with the recently introduced continuous SUN metrics. We further show that coarse MACE features can be used as guidance for a material generative model.
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All authors Paul Hagemann, Katharina Ueltzen, Simon Müller, Janine George, Philipp Benner
Materials Science
Local B-site chemistry controls oxygen-vacancy energetics in Ca-Ce-Ti-Mn perovskites for thermochemical hydrogen production
Manish Kumar, Natalia Ali, Matthew D. Witman et al. (+5 more)
Two-step thermochemical water splitting driven by concentrated solar heat is a scalable route to renewable hydrogen, but it requires oxides whose oxygen-vacancy formation energies balance facile reduction with favorable reoxidation. Perovskite solid solutions can tune this balance, but the relationship between bulk stoichiometry and local defect energetics remains poorly understood. Here we map oxygen-vacancy formation energetics across Ca-Ce-Ti-Mn (CCTM) perovskites by combining first-principles calculations with a coverage-constrained special quasirandom structure approach that realizes all fifteen
symmetry-distinct oxygen nearest-neighbor environments, an interpretable
crystal-feature model whose fitted coefficients directly encode the underlying Born-Haber thermochemistry, and a fine-tuned defect graph neural network. Local B-site chemistry dominates the oxygen-vacancy formation energy $E_\mathrm{v}$: varying the nearest-neighbor Mn fraction shifts $E_\mathrm{v}$ by 1.0-1.5 eV depending on local Ce content, whereas A-site Ce variation contributes a smaller, Mn-dependent shift of 0.2-0.6 eV. Short-range B-site cation order, if it can be established and kinetically retained through processing, is therefore a candidate means of tuning redox performance without changing bulk composition. Composition-space maps identify a Ce/Mn-balanced region ($X_\mathrm{Ce}$ = 0.29-0.33, $X_\mathrm{Mn}$ = 0.58-0.67) combining a high fraction of vacancy sites within the targeted $E_\mathrm{v}$ window with phase stability and solubility, whose predicted redox cycle capacity matches or exceeds the ceria
benchmark at 1350 $^\circ$C rather than the roughly 1600 $^\circ$C ceria requires. Measurements on three CCTM compositions show cycle capacity increasing monotonically with Ce content under protocols close to the model conditions. The design rules are expected to transfer to related perovskite families.
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All authors Manish Kumar, Natalia Ali, Matthew D. Witman, Shang Zhai, James E. Miller, Ivan Ermanoski, Ellen B. Stechel, Robert B. Wexler
Materials Science
Symmetry Rules for Cavity Materials Engineering with Linearly Polarized Vacuum Fields
Jingkai Quan, Chongxiao Fan, Benshu Fan et al. (+3 more)
Cavity materials engineering, aiming to manipulate material properties by coupling to
vacuum fluctuations inside a cavity, is a rapidly advancing field. Despite significant progress, most studies to date have focused on specific materials and cavity configurations. Here, through a comprehensive group-theoretical analysis, we establish general
symmetry rules for cavity materials engineering with linearly polarized cavity
photon modes. By analyzing the
symmetry of the Pauli-Fierz
Hamiltonian within the long-wavelength approximation, we provide a classification of the
symmetry-breaking patterns induced by cavity modes for all crystallographic point groups. The power of this framework is then demonstrated by
quantum-electrodynamical density functional theory calculations. In particular, we explain the distinct cavity-induced lifting of band degeneracies in cubic BaTiO$_3$ for different cavity mode configurations, and the cavity-modified infrared and Raman spectra of monolayer MoS$_2$ due to
symmetry breaking. Our results highlight the central role of
symmetry in cavity materials engineering and provide general guidelines for future studies in this field.
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All authors Jingkai Quan, Chongxiao Fan, Benshu Fan, I-Te Lu, Dante M. Kennes, Angel Rubio
Materials Science · Cross-listed from physics.chem-ph
Wavefunction-based periodic quantum chemistry
Hong-Zhou Ye and Timothy C. Berkelbach
High-accuracy molecular
quantum chemistry offers a promising toolbox for applications to condensed-phase systems, but this field is difficult to enter due to its combination of topics from molecular
quantum chemistry, solid-state physics, and numerical methods. Aiming to ease this transition, we present a comprehensive, pedagogical tutorial on periodic
quantum chemistry calculations, using both mean-field and correlated theories. The subtleties of periodic Coulomb interactions are discussed in detail, focusing on the Ewald summation approach. We describe the two most popular periodic, one-electron basis functions—plane waves and periodic linear combinations of atomic orbitals—and we give formulas for all
Hamiltonian integrals. Next, we explain the use of $k$-point sampling as a
symmetry adaptation of supercell basis functions and the associated savings in computational costs as well as the use of density fitting and related approximations to further reduce costs. We present the working equations of a few example periodic
quantum chemistry methods, including Hartree-Fock theory, perturbation theory, and coupled-cluster theory, and we discuss their finite-size errors and convergence to the physically relevant thermodynamic limit. Finally, we briefly discuss local correlation and
quantum embedding theories, which are especially appropriate for periodic systems due to their
lattice translational
symmetries.
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Materials Science
Drumhead Surface States of Rhombohedral Graphite with Near Ideal Quantum Geometry Condition
Lin-Lin Wang
The ideal
quantum geometry (IQG) condition of equal magnitude between
quantum metric ($G(k)$) and Berry
curvature ($\Omega(k)$) as in $|\Omega|$/Tr$G$=1 has been associated with realizing fractional Chern
insulators for the flat band in few layers of rhombohedral
graphene (RG). More recently the IQG condition has also been proposed for superconductivity in the flat band for thick RG layers. Using density functional theory and Wannier functions, we study the
symmetry-protected
topology of bulk RG, drumhead surface state (DSS) of semi-infinite RG surface, and the IQG condition for thick RG slabs. We find that bulk RG is a weak topological
insulator with
spin-orbit coupling (SOC), besides being effectively a chiral semimetal with chiral nodal line without SOC. We also find that the DSS flat band of semi-infinite and thick RG slabs have a sizable convex
curvature with depth agreeing with the recent angular resolved phono-emission spectroscopy experiment. The calculated IQG also shows a convex shape with the K point at the center having a minimum with approximately $|\Omega|$/Tr$G$$\approx$1. But the inner rim of the DSS region shows the strict IQG condition of $|\Omega|$/Tr$G$=1. These results on semi-infinite and thick RG slabs from first-principles calculations provide useful information for the pristine DSS at the single particle level for future studies to consider when many-body interactions and strong correlations will be included.
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Materials Science · Cross-listed from physics.comp-ph
Fast and Accurate Equivariant Foundation Models for Atomistic Simulation
Seán R. Kavanagh, Chuin Wei Tan, Menghang Wang et al. (+12 more)
Machine-learned interatomic potentials (MLIPs) have emerged as a transformative tool for computational materials science and chemistry, with universal potentials trained on large and diverse
datasets now routinely deployed as 'foundation models' for downstream fine-tuning in targeted chemical spaces. Many scientific applications of the resulting models, such as molecular dynamics (MD), require high inference and training speeds as well as accuracy. In this work, we examine the limits of equivariant MLIPs, which directly encode physical
symmetries in model architectures, to achieve these competing targets – particularly in the regime of extremely large
datasets where data efficiency is less critical. We show how this trade-off can be addressed, and present a family of foundation potentials in the NequIP and Allegro equivariant MLIP architectures which achieve leading inference speeds and strong scalability as well as excellent accuracies across a range of community
benchmarks – spanning materials discovery, thermal conductivity prediction, and near-
equilibrium mechanical and thermodynamic properties. Accelerations implemented within the NequIP infrastructure now permit training of high-accuracy foundation potentials on ultra-large
datasets with dramatically reduced computational cost. Alongside, we show that efforts to improve model accuracy for materials discovery should focus on
dataset diversity and improved, consistent descriptions of transition metal compound energy surfaces.
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All authors Seán R. Kavanagh, Chuin Wei Tan, Menghang Wang, Marc L. Descoteaux, Gabriel de Miranda Nascimento, Ulrik Unneberg, Laura Zichi, Francesco Libbi, Norma Rivano, Austin Glover, Vivek Bharadwaj, Anders Johansson, William C. Witt, Albert Musaelian, Boris Kozinsky
Materials Science · Cross-listed from cond-mat.str-el
Field-Selected Topological Buffering in a Disordered Skyrmion Crystal
Wenyu Su, Nvsen Ma, Chen Cheng et al. (+1 more)
Quenched disorder can disrupt crystalline order without immediately destroying the
topology of its constituent textures, but the relation between these processes in skyrmion
crystals remains unclear. Using large-scale simulations of a triangular-
lattice chiral magnet with random DM interactions, we show that the
magnetic field selects between two disordering routes. At high fields, global translational coherence is lost at a weak-disorder scale, while sixfold bond-orientational order survives to a larger disorder strength and the total topological charge remains nearly locked up to a substantially larger scale. The resulting interval defines a topological buffer containing a Bragg-glass- like skyrmion regime followed by a skyrmion-glass regime. Finite-size scaling, spatial correlations, defect statistics, and
spin autocorrelations support their distinct structural and glassy character. At lower fields, bond-orientational disordering nearly coincides with topological reconstruction, eliminating the skyrmion-glass window and contracting the buffer. These results identify the
magnetic field as a control knob for separating crystalline disordering from topological-charge loss and establish topological buffering as a mechanism by which topological textures can remain robust in structurally disordered media.
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All authors Wenyu Su, Nvsen Ma, Chen Cheng, Hong-Gang Luo
Materials Science
Transport Evidence of Magnetic Polarization in the Altermagnetic Candidate MnTe
Younes Ghorbani, Nayana Devaraj, Joshua Maile et al. (+7 more)
The ability to precisely control
magnetic properties is central to the development of future
spin-based electronics. In this work, we report the successful growth of epitaxial {\alpha}-MnTe thin films on InP(111) substrates using molecular beam epitaxy. Magneto-transport measurements at low temperatures reveal a distinct, hysteretic butterfly longitudinal magnetoresistance alongside a nonlinear transverse magneto-resistance response, suggesting the presence of a finite net
magnetic polarization in the films. To understand the origin of this behavior, density functional theory (DFT) calculations were performed. While pristine bulk MnTe is a compensated antiferromagnet, our computational results suggest multiple pathways through which a finite magnetization can emerge in thin-film geometries, including interface-induced
symmetry breaking and point defects. These findings demonstrate an epitaxial route for engineering
magnetic responses in thin films.
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All authors Younes Ghorbani, Nayana Devaraj, Joshua Maile, Samuel Poage, Qihua Zhang, Maria Hilse, Stephanie Law, Salva Salmani-Rezaie, Awadhesh Narayan, Kaveh Ahadi
Materials Science
Hydration-Controlled Layer Stacking in (NH$_3$)$_2$Cu$_5$(SeO$_3$)$_2$(OH)$_6$(H$_2$O)$_{2+x}$ ($x$ = 0, 1, and 3)
Priya R. Baral, Christian Jandl, Pauline Pradal et al. (+3 more)
Hydration and dehydration are powerful yet underexplored variables for controlling the architecture of layered inorganic materials, because intercalated water can modify interlayer separation, hydrogen-bonding networks, and layer stacking. Here, we report the reflux synthesis of a new family of hydrated layered copper selenites, (NH$_3$)$_2$Cu$_5$(SeO$_3$)$_2$(OH)$_6$(H$_2$O)$_{2+x}$ ($x$ = 0, 1, and 3). From the
crystal structures determined using electron diffraction and single
crystal X-ray diffraction, we deduce that all three compounds share an identical layer built from Cu(OH)$_4$ squares and Cu-centered square pyramids forming distorted kagomé-like Cu$^{2+}$ network. While the intralayer atomic arrangement is preserved across the series, the degree of hydration governs both the interlayer separation and the stacking sequence. These compounds therefore provide a rare platform relevant to the design of hydration-responsive materials for sensing, ion transport, separations, actuation, and energy-related applications. The preservation of distorted kagomé-like Cu$^{2+}$ layers across hydration states further suggests potential interest for examining how interlayer water and stacking sequence affect low-dimensional
magnetic coupling. Under reflux conditions, these phases are also shown to act as reactive intermediates in the formation of Cu$_2$OSeO$_3$, establishing them as tunable precursors for copper oxoselenite synthesis.
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All authors Priya R. Baral, Christian Jandl, Pauline Pradal, Johann Roos, Wenhua Bi, Arnaud Magrez
Materials Science
Quasiparticle phono-conversion: filming carriers coalescing into excitons
Enrico Perfetto, Takumi Fukuda, Xing Zhu et al. (+12 more)
Condensed matter physics is replete with phenomena involving high-energy free particles coalescing into low-energy bound few-particle states. While the cooling of the individual particles is well understood, the crucial step by which cold free carriers form a bound state remains elusive, involving complex energy and momentum relaxation pathways. Here, by combining ultrafast time- and momentum-resolved photoemission spectroscopy on a monolayer WSe$_2$ with the first-principles excitonic-Bloch equations, we resolve the conversion of initially free electrons and holes at the bandedges into bound
excitons. With unprecedented energy resolution, we observe the transient coexistence of free-carrier and excitonic bands, accompanied by a transfer of spectral weight between the two. We establish the phononic origin of
exciton formation and ascribe this coexistence to a sequential relaxation cascade toward the lowest-energy excitonic states, wherein intermediate states remain weakly populated. The efficiency of this process is controlled by valley multiplicity, large-momentum
phonon emission and
spin-flip processes. By elucidating how bound states emerge from their elementary constituents, our results point to strategies for engineering
exciton formation, with direct implications for optical materials and devices that operate with
excitons or free carriers.
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All authors Enrico Perfetto, Takumi Fukuda, Xing Zhu, Jacques Hawecker, Harley Suchiang, Joanna Nadolna, Nanami Tomoda, Suji Park, Houk Jang, Kenji Watanabe, Takashi Taniguchi, Michael K. L. Man, Julien Madéo, Keshav M. Dani, Gianluca Stefanucci
Materials Science
Charge-to-spin conversion in epitaxial and polycrystalline Bi and Bi/Ag layers
Federica Nasr, Emir Karadža, Santos F. Alvarado et al. (+9 more)
Bi is predicted to be an efficient generator of
spin-orbit torques (SOTs), with charge-to-
spin conversion efficiency comparable to those of prototypical heavy metals, such as Ta, W, and Pt. However, experimental reports provide widely scattered interconversion efficiencies, while the origin of the large conversion signal in Bi/Ag bilayers remains controversial. Here, we investigate charge-to-
spin conversion in epitaxial and polycrystalline Bi-based
magnetic heterostructures by measuring the damping-like SOT using magneto-optic Kerr effect magnetometry, complemented by structural and spectroscopic analyses and harmonic Hall resistance measurements. We show that inserting an Ag spacer between Bi(001) and metallic ferromagnets (FeCo or Ni) enhances the SOT efficiency by more than one order of magnitude, reaching an effective
spin Hall conductivity of approximately $2 \times 10^5 (\hbar/2e)$ S/m, in excellent agreement with theoretical expectations for bulk Bi. This enhancement can be consistently explained by the preservation of the structural and chemical integrity of Bi, otherwise compromised by the direct deposition of a ferromagnetic overlayer, rather than by Rashba
spin-orbit coupling at the Bi/Ag interface. Comparative studies across epitaxial, polycrystalline, and intentionally surface-oxidized Bi films, beyond oxygen doses known to destroy Bi(001) surface states, reveal that structural disorder has a negative impact on the SOT efficiency and indicate a dominant bulk contribution to
spin-current generation in Bi/Ag
heterostructures, yielding an effective Bi
spin Hall angle of approximately 1. By establishing a direct correlation between atomic-scale integrity and charge-to-
spin conversion, this study provides design principles to improve the reliability of Bi-based SOT devices and offers a robust framework for interpreting
spin-charge interconversion in Bi and Bi/Ag systems.
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All authors Federica Nasr, Emir Karadža, Santos F. Alvarado, Federico Binda, Tobias Goldenberger, Carlo Zucchetti, Myriam H. Aguirre, Paolo Moras, Andrey V. Matetskiy, Polina M. Sheverdyaeva, Paul Noël, Pietro Gambardella
Materials Science · Cross-listed from cond-mat.mes-hall
Effects of gold cluster intercalation in graphene: stationary waves and modified QPI features
Cristina Bena, Marion Cranney, Poonam Kumari et al. (+2 more)
Gold intercalation beneath epitaxial
graphene on SiC produces a cluster phase with unusual standing waves and quasiparticle-interference (QPI) features concentrated near the
graphene M points. We show that this can be explained by Au intercalation below
graphene hollow sites, which induces a local scattering potential on the six surrounding carbon atoms. Within a T-
matrix treatment, this ring-like scatterer produces elliptical QPI structures centered near M, in agreement with the experimental FT-STS measurements. We further show that these QPI features naturally generate the nearly stationary standing-wave patterns observed in real space. Finally, we compute the local-density-of-states contrast on and off a small cluster and show that its sign and magnitude are strongly energy dependent, consistent with the experimental observations.
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All authors Cristina Bena, Marion Cranney, Poonam Kumari, Alberto Zobelli, Laurent Simon
Materials Science · Cross-listed from cond-mat.mes-hall
An iterative method bridging DFT, disorder averaging, and experiment in intercalated materials: application to Au-intercalated graphene
Poonam Kumari, Alberto Zobelli, Igor de Melo Froldi et al. (+3 more)
Intercalation can strongly modify the electronic dispersion of a host material, as directly revealed by angle-resolved photoemission spectroscopy (ARPES). We develop a general iterative method combining density functional theory (DFT), tight-binding (TB), disorder averaging within the self-consistent T-
matrix approximation (SCTMA), and experiment, to construct an effective model of the intercalated system. DFT identifies the relevant microscopic degrees of freedom and constrains selected model parameters, while comparison of SCTMA calculations with experiment guides their further refinement. We apply this method to
graphene intercalated with Au clusters and show that it reproduces the main ARPES signatures of the Au-cluster phase, including the broadening of the V12an Hove singularity and the emergence of kink-like features in the dispersion. The essential microscopic ingredients identified by the analysis are the hybridization between selected intercalant orbitals and the
graphene states, together with an intercalation-induced local scattering potential.
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All authors Poonam Kumari, Alberto Zobelli, Igor de Melo Froldi, Adeline Crepieux, Laurent Simon, Cristina Bena
Materials Science
Intertwined magnetoresistance and Hall multifunctionality in a non-coplanar magnetic Weyl semimetal DyB4
Long Chen, Yulin Shen, Songxue Chi et al. (+4 more)
Anomalous magneto-transport responses provide complementary probes of orbital motion, momentum-space
topology, and real-space
spin chirality, yet their integration into a single material remains rare because their underlying requirements often compete. A promising materials-design strategy is to realize a
magnetic Weyl semimetal that combines linearly dispersive high-mobility bands with tunable non-coplanar magnetism while limiting
spin-dependent scattering. Here we identify DyB4, a frustrated rare-earth tetraboride, as a
magnetic Weyl semimetal candidate that embodies this strategy and hosts intertwined magnetoresistance and Hall multifunctionality.
Neutron diffraction reveals a sequence of field-tunable
magnetic states, including non-coplanar
spin configurations and PT-
symmetry-broken phases. First-principles calculations identify steep linear dispersions and field-induced Weyl points near the Fermi level. Magneto-transport measurements establish a rare fourfold combination of extremely large magnetoresistance, chiral-anomaly-like negative magnetoresistance, large anomalous Hall conductivity arising from cooperative intrinsic Berry
curvature and skew scattering, and scalar-
spin-chirality-driven topological Hall responses. This multifunctionality arises from the distinct yet weakly coupled roles of itinerant carriers and localized 4f moments, which enable high-mobility transport, field-induced Weyl
topology, and non-coplanar magnetism. DyB4 therefore provides a 4f-electron platform for correlating orbital transport, momentum-space Berry
curvature, and real-space
spin chirality, suggesting a route toward multifunctional
magnetic topological materials.
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All authors Long Chen, Yulin Shen, Songxue Chi, Seunghoon Song, Yang Zhang, Jian Liu, Haidong Zhou
Materials Science
"Anomalous Solid Solution" in Ultra-High Melting Point Oxides: A New Strategy for Developing Ultra-High Temperature Thermal Protection Coatings
Yubo Wang, Hong Meng, Pengfei He et al. (+7 more)
The high-temperature performance of ultra-high temperature ceramics (UHTCs) in atmospheric environment is fundamentally governed by their melting points of oxidation products. Typical high-melting-point oxides, such as ZrO2, undergo phase transformations at elevated temperatures, leading to structural instability. Although doping with rare-earth or transition-metal cations can suppress these transformations, it often results in a reduction in melting point, thereby limiting practical service temperature. Here, ytterbia-stabilized zirconia (YbSZ) coatings are prepared via atmospheric
plasma spraying, achieving a remarkable increase in the melting point of ZrO2 to approximately 2850 $^\circ\mathrm{C}$ and raising the ultimate
plasma and oxyacetylene ablation temperature up to nearly 2780 $^\circ\mathrm{C}$ and 3200 $^\circ\mathrm{C}$, which is the highest temperature resistance property as reported. Notably, this performance enhancement originates from a synergistic mechanism of strengthened ionic-covalent mixed bonding and improved oxygen vacancy stability. Based on these findings, the concept of "anomalous solid solution" is firstly proposed to be used in the area of ultra-high temperature protection, which provides new insights into the compositional design of UHTC systems.
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All authors Yubo Wang, Hong Meng, Pengfei He, Shujun Hu, Chuan Sun, Ximing Duan, Xiaopeng Lu, Dingwang Yuan, Wangyu Hu, Xiubing Liang
Materials Science
Negative Thermal Expansion in Cubic Ice: A Collective Quantum Effect of the hydrogen-bond network
Loan Renaud, Tomasz Poreba, Richard Gaal et al. (+3 more)
We report
neutron powder diffraction measurements and path-integral molecular dynamics simulations of stacking-disorder-free cubic ice I$_c$, produced by topotactic degassing of C2 hydrogen hydrate. Across the cryogenic stability range, ice I$_c$ exhibits a density maximum near 70 K, closely matching that of hexagonal ice I$_h$ despite their different long-range stacking sequences. Negative thermal expansion in ice I is therefore not specific to hexagonal stacking, but arises from the shared open tetrahedral hydrogen-bond network. Simulations with the MB-pol potential quantitatively reproduce the experimental anomaly only when nuclear
quantum effects are included. The density maximum coincides, within the temperature resolution, with maximal anisotropy of the
proton quantum distribution.
Neutron-derived displacement parameters independently reveal a strongly enhanced transverse
proton displacement, while
phonon calculations identify low-frequency transverse modes with the most negative Grüneisen parameters. Together, these results establish the negative thermal expansion of ice I as a collective
quantum effect governed by nuclear statistics and the dynamics of the hydrogen-bond network.
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All authors Loan Renaud, Tomasz Poreba, Richard Gaal, A. Marco Saitta, Michele Casula, Livia Eleonora Bove
Materials Science · Cross-listed from physics.app-ph
Vibe-FDTR: An agent-oriented framework for reproducible frequency-domain thermoreflectance data analysis
Fuwei Yang, Weiheng Li and Bai Song
Frequency-domain thermoreflectance (FDTR) is a
laser pump-probe technique widely used to measure thermal properties at the micro- and nanoscale; however, it relies on a complex data analysis procedure that demands substantial domain expertise and is susceptible to subtle human errors. Here, we present Vibe-FDTR, an
agent-oriented framework that enables large
language model (LLM)
agents to perform reliable and reproducible FDTR analyses directly from natural
language requests. This framework couples a configuration-driven FDTR code package, which enforces physical and parametric consistency, with procedural
agent skills that translate user intentions into organized and verifiable analysis steps. We evaluate Vibe-FDTR using a controlled
benchmark with two levels: synthetic single-step tasks and real-data multi-step tasks based on measurements of gold-coated graphite samples. Across the two levels,
agents using Vibe-FDTR achieve success rates of 100% and 98.9%, respectively. In sharp contrast, ablating skills (Code-
agent) reduces performance to 91.4% and 36.7%, which drops further to 38.6% and 0% when the domain package is also omitted (
Agent-only). Beyond success rate, Vibe-FDTR also reduces computational cost by 87.7% relative to the Code-
agent variant and cuts execution time by more than 60%. Finally, an optional expert mode supports experimental planning via autonomous sensitivity and uncertainty evaluations, and formulates physically grounded recommendations for underspecified tasks. These results demonstrate that encapsulating domain code and expert knowledge into
agent skills offers a promising route toward low-barrier, autonomous, and trustworthy thermal metrology.
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Materials Science · Cross-listed from physics.optics
Spin-canting-induced Giant Nonlinear Optical Magnetochirality in a 2D Ferrotoroid
Shian Xia, Sheng Liu, Wenhe Jia et al. (+9 more)
Achieving magnetically switchable chiral light emission is an important goal for 2D opto-spintronics. However, conventional strategies face a fundamental trade-off between dynamic tunability and polarization contrast. Nonlinear optics, particularly the emerging mechanism of chiral second-harmonic generation (SHG), offers a distinct strategy to bypass this restriction, yet its experimental realization remains elusive due to stringent
symmetry requirements. Here, we report giant nonlinear optical magnetochirality in a centrosymmetric 2D ferrotoroid, bilayer (2L) CrSBr. We reveal that a field-induced
spin-canting state breaks the parity-time (PT)
symmetry of the unperturbed antiferromagnetic (AFM) ground state, activating a
spin-chirality-driven i-type susceptibility. The coherent interference between this emergent i-type and intrinsic c-type SHG susceptibilities generates a macroscopic circularly polarized SHG signal whose helicity is magnetically switchable. Leveraging this sensitive mechanism, we uncover remanent
magnetic states after field saturation that evade conventional linear probes. By exploiting the non-
volatility of these states, we demonstrate magneto-optical
memory and logic operations. Our work establishes a general
symmetry-driven strategy for tailoring nonlinear magnetochirality, while providing a sensitive optical probe for subtle
spin textures in the 2D limit.
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All authors Shian Xia, Sheng Liu, Wenhe Jia, Fanglu Qin, Xuanji Wang, Haixiang Luo, Yue Sun, Vanessa Li Zhang, Wenduo Chen, Jiazheng Qin, Cheng-Wei Qiu, Ting Yu
Materials Science · Cross-listed from cond-mat.str-el
Many-Body Amplification of Ligand Instabilities Driving Verwey-Type Transitions in Altermagnet CsCr$_2$S$_2$O
Xiuhua Chen and Yilin Wang
Altermagnet CsCr$_2$S$_2$O undergoes a Verwey-type metal-to-
insulator transition (MIT), accompanied by a
lattice distortion and stripe charge order on the Cr sublattice. Intriguingly, the atomic distortions occur exclusively at the ligand sites rather than the Cr sites, leaving the origin of the pronounced Cr charge disproportionation unresolved. Using density functional theory plus dynamical mean-field theory (DFT+DMFT) calculations, we identify an orbital-selective Mott state in which the correlated metallic $d_{yz}$ orbital governs the low-energy physics. We show that S-site distortions produces only a small bare charge asymmetry between the Cr sublattices through Cr-$d_{yz}$–S-$p$ hybridization. Dynamical electronic correlations, however, dramatically amplify this asymmetry, producing pronounced differentiation in both the charge occupancy and correlation strength of the $d_{yz}$ orbitals. The resulting site-dependent
spin polarization ultimately drives the MIT. In contrast, replacing S with Te substantially weakens this correlation-amplification effect and preserves a metallic state. Our work reveals a hidden, correlation-amplified feedback loop between ligand instabilities and electronic
symmetry breaking in this altermagnetic family, highlighting ligand engineering as an effective route toward robust metallic altermagnetism.
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Materials Science
Mapping the influence of symmetry breaking in structure-property relationships of ABO$_3$ perovskites
Panupol Untarabut, Sylvian Cadars, Fabien Pascale et al. (+5 more)
Perovskite oxides have emerged as an important class of material with promising energy applications owing to their compositional and structural flexibility, which enables stabilization of both low- and high-
symmetry phases and gives rise to diverse physical properties. Under ambient conditions, most perovskites adopt low-
symmetry structures characterized by octahedral tilting and B-site displacements. Despite their importance, computational studies have largely focused on the ideal cubic phase as modeling these distortions remains challenging. The difficulty stems from the absence of a quantitative framework capable of capturing composition-dependent distortions that can occur through multiple non-equivalent atomic displacement modes, often requiring computationally expensive large supercells to explore the structural landscape. Consequently, the influence of distortions on the stability and properties of low-
symmetry perovskites remains insufficiently understood. In this work, we develop an efficient computational framework for the rapid construction and exploration of composition-dependent structural models across both low- and high-
symmetry phases. Using $\textit{symmetry constrained templates}$ and $\textit{unconstrained supercell templates}$, we systematically investigate 15 representative compositions to uncover relationships between composition, supercell size and shape, and distortion patterns. Based on these insights, we propose a robust and computationally inexpensive protocol for rapid structural exploration and assess the influence of different distortion modes on key physical properties.
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All authors Panupol Untarabut, Sylvian Cadars, Fabien Pascale, Sébastien Lebègue, Olivier Masson, Samuel Bernard, Assil Bouzid, Santanu Saha
Materials Science
PASS: Perturbation augmented space group structure sampling for transferable Fe-O machine learning interatomic potential
Zixiong Wei, Fei Shuang and Poulumi Dey
Accurate atomistic modelling of iron (Fe) oxidation requires a reliable interatomic potential, which necessitates an extensive and representative first-principles
dataset for training the interatomic potential. However, Fe-oxygen (O) system is known for its structural and
magnetic complexity, rendering the generation of high-quality
dataset challenging. In this work, we propose the Perturbation Augmented Space group structure Sampling (PASS) method to generate extensive and representative
dataset consisting of small-
cell structures with less than 10 atoms. We present a systematic approach to developing a first of its kind transferable machine learning interatomic potential (MLIP) for Fe-O system based on the atomic cluster expansion (ACE) framework. We thoroughly validate the accuracy and capability of the ACE MLIP across both pure Fe and Fe-O systems through bulk, surface, and interface properties. We showcase the formation of FeO-like structure in large-scale Fe oxidation simulation using the ACE MLIP. This work demonstrates that the PASS method yields an accurate and transferable MLIP which is capable of capturing the reactive complexity of oxide growth while remaining computationally practical for extended systems.
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Materials Science
Tunable Conformal Graphene Growth on Oxide Nanotube scaffolds: Towards Superwettable Hierarchical 2D-3D Architectures
Fernando Nunez Galvez, Muhammad Hamza, Johannes Berndt et al. (+7 more)
Hierarchical hybrid nanoarchitectures that integrate vertically oriented
graphene nanowalls, GNWs, with metal oxide, MeOx, nanotube scaffolds offer versatile platform for smart surfaces, nanoelectronics, and electrochemical technologies. Herein we present rapid, dry,
plasma-assisted fabrication route that enables direct and conformal growth of GNWs on mechanically robust MeOx nanoforests. The method combines supported single-crystalline organic nanowires as a 1D soft template with sequential
plasma-enabled oxide deposition and GNW growth, all performed under mild temperature, power, and
vacuum conditions. This approach yields an unprecedented 2D-3D hierarchical architecture consisting of tunable-thickness MeOx nanotubes uniformly decorated with radially oriented
graphene nanosheets, forming re-entrant, multiscale surface. Resulting hierarchical roughness imparts fluorine-free, long-term omniphobicity, with contact angles exceeding 170 degree for water, bovine serum, and other complex fluids. GNWs dominate the wetting response across TiO2, Al2O3, and SiO2 nanotube scaffolds, effectively decoupling surface behavior from intrinsic oxide chemistry and maintaining robust repellency under UV irradiation and water condensation. Comprehensive SEM, TEM, XPS, angle-resolved NEXAFS, and Raman analyses elucidate growth mechanism and confirm preservation of the sp2 graphitic framework, together with controlled degree of edge functionalization. Overall, this work establishes universal, substrate-compatible, low-temperature, and scalable route for the fabrication of tunable
graphene-metal oxide nano-microstructured multifunctional surfaces.
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All authors Fernando Nunez Galvez, Muhammad Hamza, Johannes Berndt, Thomas Strunskus, Franziska Traeger, Nicolo di Novo, Juan R. Sanchez-Valencia, Carmen Lopez-Santos, Ana Borras, Eva Kovacevic
Materials Science
STM study of single phosphorus incorporation into silicon by heating PBr3 on Si(100)
Tatiana V. Pavlova and Vladimir M. Shevlyuga
The objective of miniaturizing doped areas in silicon, with the ultimate goal of achieving atomic-precision doping, requires a fundamental understanding of the dopant incorporation process at the atomic level. We present a combined scanning tunneling microscopy (STM) and density functional theory (DFT) investigation of single phosphorus atom incorporation into the Si(100) surface. Phosphorus was supplied via PBr3 molecules, which completely dissociate on Si(100) at room temperature. By performing in situ annealing within the STM, we directly tracked the same phosphorus atom before and after heating. Upon annealing, the P atom undergoes an exchange with a nearby Si atom, forming a stable P-Si-Br complex with a Br atom located atop the Si atom of the heterodimer. The activation barrier calculated using DFT is consistent with our observation of doping starting at temperatures as low as 175 C. These results provide detailed atomic-scale insight into the phosphorus incorporation pathway and offer a foundation for improving methods of precise, single-atom doping in silicon.
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