Materials Science
Achieving Large Uniaxial and Homogeneous Strain in Two-Dimensional Materials
Yangchen He, Jessica Kienbaum, Wuzhang Fang et al. (+4 more)
Strain engineering is a powerful tool for tuning the electronic,
magnetic, and topological properties of two-dimensional (2D) materials and thin films - particularly at high values of strain (>3%) where many electronic,
magnetic, and structural transitions have been predicted. However, most approaches to tuning strain in 2D materials are limited below 1.5%, with poor repeatability when cycling strain and low strain transfer when cooling to cryogenic temperatures. Here, we report a high-yield sample preparation and device strain platform that overcomes these limitations, enabling precise, reversible strain tuning up to the intrinsic strain-to-failure of the materials tested herein. In addition, we show that this platform can be used to controllably design uniform linear strain gradients across of 10's of $\mu$m, providing a novel route to systematically investigate flexoelectric and flexomagnetic phenomena. Using CrSBr as a model system, we demonstrate uniform uniaxial strain, up to ~4%, with negligible slippage and linear strain gradients of up to 0.06%/$\mu$m. We further show that our strain approach is applicable to a broad class of 2D materials, validating its performance for three different phases of transition metal dichalcogenides: 2H-MoTe$_2$, 1T$^\prime$-MoTe$_2$ and T$_\mathrm{d}$-WTe$_2$. In T$_\mathrm{d}$-WTe$_2$, verified by theoretical calculations, we show a continuous
redshift of the A$_1^3$ mode, up to a record-breaking ~5.5% strain, with a clear separation of the A$_1^3$ and A$_1^2$ modes starting at 2% strain.
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All authors Yangchen He, Jessica Kienbaum, Wuzhang Fang, Hongrui Ma, Ying Wang, Ping Yuan, Daniel A. Rhodes
Materials Science
First-Principles Study of Structural, Electronic, Thermal, and Optical Properties of Quasi-2D C2 N2 O Using GGA and HSE06
Hemn. G. H, Nzar. R. Abdullah and Vidar Gudmundsson
DFT and AIMD are used to investigate the structural, stability, electronic, thermal, and optical properties of the quasi-2D C2N2O structure. The structure exhibits thermal and energy stability, signifying robustness under ambient conditions, however less dynamical stability is observed. The electronic structure investigation reveals that C2N2O displays semiconducting properties with a moderate indirect band gap resulting from the hybridisation of p-orbitals of N, C, and O atoms, with band gap values of 2.3 eV (GGA) and 3.9 eV (HSE06). The optical properties, including the dielectric function, optical conductivity, and refractive index, are thoroughly analyzed to clarify the electronic transitions. The material exhibits considerable optical absorption in the visible and ultraviolet spectrum, with notable anisotropy between in-plane and out-of-plane polarizations. Furthermore, plasmon resonance occurs at around 3.8 eV, relating to the collective oscillations of charge carriers. The thermal properties indicate a heat capacity of around 382 J/mol.K at 300 K, which is close to and slightly above the standard Dulong-Petit limit for this structure, indicating near-complete excitation of
lattice vibrational modes at room temperature. The
lattice thermal conductivity is extremely low, reaching approximately 0.017 W/m.K at 300 K, primarily attributed to significant
phonon scattering, evidenced by a scattering rate of roughly 3.2 1/ps in the
phonon frequency ranges. The findings demonstrate that the C2N2O structure maintains structural stability while allowing for tunable electronic, optical, and thermal properties, making it a promising candidate for nanoscale optoelectronic and thermal control applications.
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Materials Science · Cross-listed from physics.comp-ph
Mixture of Experts Framework in Machine Learning Interatomic Potentials for Atomistic Simulations
Gabriel de Miranda Nascimento, Marc L. Descoteaux, Laura Zichi et al. (+9 more)
First-principles atomistic simulations are essential for understanding complex material phenomena but are fundamentally limited by their computational cost. While Machine Learning Interatomic Potentials (MLIPs) have drastically improved cost for a given accuracy, their inference cost remains a bottleneck for massive systems or long timescales. To address this, we introduce a multifidelity "Mixture-of-Experts" framework based on the E(3)-equivariant Allegro architecture. Our method spatially partitions the simulation domain into a chemically complex region (e.g., reactive interfaces) and a simple region (e.g., bulk
lattice), assigning models of varying capacity to each. Among the challenges in such static domain decomposition, the mechanical mismatch between models at the interface is particularly critical, as it can generate artificial stress fields and instability. We address this challenge with a co-training strategy in which the loss function includes agreement constraints – penalties on per-atom energy and force discrepancies between models evaluated on shared bulk environments – forcing the independent models to learn a consistent physical description of the bulk material. We validate this approach on a realistic Pt+CO catalytic system, demonstrating that the co-trained models maintain exact energy conservation, align their bulk mechanical response (e.g., equation of state and bulk modulus), and achieve predictive accuracy comparable to a full high-fidelity simulation at more than twice the computational speed.
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All authors Gabriel de Miranda Nascimento, Marc L. Descoteaux, Laura Zichi, Chuin Wei Tan, William C. Witt, Nicola Molinari, Sriteja Mantha, Daniil Kitchaev, Mordechai Kornbluth, Karim Gadelrab, Charles Tuffile, Boris Kozinsky
Materials Science
Implementation of the hybrid exchange-correlation functionals in the SIESTA code
Yann Pouillon, Bill Clintone Oyomo, James Sifuna et al. (+6 more)
We present an efficient and accurate implementation of hybrid exchange-correlation (XC) functionals in the SIESTA code, enabling large-scale simulations based on Hartree-Fock-type exact exchange combined with strictly localized numerical atomic orbitals (NAOs). Our approach exploits a fitted representation of the NAOs in terms of Gaussian-type orbitals (GTOs), which allows for the analytical evaluation of four-center electron repulsion integrals (ERIs) via the LIBINT library. This framework is seamlessly integrated with SIESTA's real-space grid and sparse-
matrix infrastructure, and is combined with multiple screening techniques to control the computational complexity. We also introduce a fully analytical formulation of hybrid-functional forces and a dynamic parallel distribution scheme that ensures excellent scalability. We validate our implementation through
benchmark calculations on a broad set of systems (including
semiconductors,
insulators, and two-dimensional materials) and demonstrate that the HSE06 functional significantly improves the prediction of band gaps compared to PBE, in close agreement with G0W0 and experimental data. We analyze in detail the trade-offs between accuracy and computational efficiency as a function of the number of Gaussians, basis set range, and integral screening thresholds. Our results confirm that hybrid functional calculations in SIESTA are now feasible for large extended systems, making accurate first-principles predictions of electronic and structural properties accessible at scale.
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All authors Yann Pouillon, Bill Clintone Oyomo, James Sifuna, María Camarasa-Gómez, Xinming Qin, Carlos Beltrán, Fernando Gómez-Ortiz, Honghui Shang, Javier Junquera
Materials Science
Hidden Crossover and Relaxor-Like Response from Emerging Polar Skyrmion Correlations in Ferroelectric Superlattices
Zhiyang Wang, Fei Yang and Long-Qing Chen
Polar skyrmions in ferroelectric superlattices are nanoscale topological polarization textures typically regarded as weakly coupled objects confined to individual layers, with a role secondary to that of the underlying
symmetry-breaking order parameter. Here using large-scale phase-field simulations of ferroelectric superlattices, we uncover a hidden thermal crossover deep inside the ferroelectric phase, where polar skyrmions evolve from an uncorrelated, layer-resolved state into an interlayer-correlated ensemble. This crossover occurs without additional
symmetry breaking or a new order parameter, but produces a pronounced broad peak in the dielectric susceptibility. The anomaly originates from the competition between correlation-enhanced response, associated with the growth of interlayer skyrmion correlations, and polarization-induced stiffness, which suppresses dielectric fluctuations at low temperature. Under AC driving, the peak shifts with frequency, resembling relaxor ferroelectrics despite the absence of quenched disorder or polar nanoregions. Our results establish a disorder-free route to relaxor-like dielectric response and identify topological defect correlations as an organizing principle for thermodynamic anomalies, providing a mechanism distinct from conventional critical behavior associated with
symmetry breaking and divergent order-parameter fluctuations.
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Materials Science
Domain-induced control of latent heat in freestanding BaTiO$_3$ membranes
Tapas Bar, David Pesquera, Arnau Villalobos-Martin et al. (+11 more)
Thin ferroelectric BaTiO$_3$ films often exhibit continuous transitions instead of the first-order behavior of bulk
crystals, a discrepancy usually attributed to epitaxial strain or dimensionality. Using quasi-adiabatic nanocalorimetry on freestanding BaTiO$_3$ membranes-free of clamping and substrate heat sinking-we show that domain morphology, not thickness or boundary conditions, controls the transition order. Thick membranes with large, monodomain-like regions display clear latent heat, whereas thinner membranes with dense 180$^{\circ}$ domain patterns show a continuous transition despite undergoing the same tetragonal-cubic structural change confirmed by x-ray diffraction. Piezoresponse force microscopy links this behavior to domain-size
evolution, and a Ginzburg-Landau analysis demonstrates how reduced domain size lowers the free-energy barrier, rounding a nominally first-order instability. These results identify domain morphology as the key determinant of ferroelectric transition order in
oxide membranes and establish design guidelines for enhancing caloric effects through domain engineering.
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All authors Tapas Bar, David Pesquera, Arnau Villalobos-Martin, Cristian Rodriguez-Tinoco, Umair Saeed, Kumara Cordero-Edwards, Jessica Padilla, Jose Manuel Caicedo Roque, Jose Santiso, Pol Lloveras, Leo Boron, Igor Lukyanchuk, Gustau Catalan, Javier Rodriguez-Viejo
Materials Science · Cross-listed from physics.comp-ph
Accelerating finite-element-based projector augmented-wave DFT calculations with scalable GPU-centric computational methods
Kartick Ramakrishnan and Phani Motamarri
Accurate large-scale Kohn-Sham density functional theory (DFT) calculations are essential for modeling complex material systems, including interfaces, defects, nanoclusters, and twisted two-dimensional
heterostructures. Achieving chemical accuracy at scales of $10^4$-$10^5$ electrons with practical time-to-solution, however, remains challenging for existing DFT implementations. We present GPU-centric computational methods and algorithmic innovations within a finite-element (FE) discretized projector augmented-wave (PAW) formulation (PAW-FE) for accurate, efficient, and scalable electronic-structure calculations on modern exascale systems. The FE discretization, developed within a collinear
spin formalism, accommodates generic boundary conditions and employs multi-resolution quadrature for accurate evaluation of atom-centered PAW integrals on coarse grids. The resulting generalized Hermitian eigenproblem is solved using residual-based Chebyshev filtered subspace iteration (R-ChFSI). Exploiting R-ChFSI's tolerance to inexact
matrix-multivector products, we employ an approximate inverse PAW overlap
matrix, mixed-precision arithmetic (FP32/TF32), and low-precision nearest-neighbor communication (BF16) during filtered subspace construction, along with block-wise computation-communication overlap to reduce cost while preserving robustness. These strategies yield up to $8\times$ and $20\times$ CPU-GPU speedups on Intel and AMD GPU architectures, respectively. Compared to plane-wave PAW methods, PAW-FE achieves close to 8$\times$ reduction in time-to-solution for 10,000-electron systems on NVIDIA GPUs, with larger gains at scale, and around 6$\times$ over norm-conserving FE approaches. We demonstrate scalability to 130,000-electron systems, establishing PAW-FE as an exascale-ready method for chemically accurate first-principles simulations.
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Materials Science · Cross-listed from cond-mat.mes-hall
Magnetononlinear Hall effect from multigap topology in metal-organic frameworks
Chun Wang Chau, Wojciech J. Jankowski, Bo Peng et al. (+1 more)
We unveil that non-Abelian multigap band
topology characterized by nontrivial Euler class invariants induces observable magnetononlinear
Hall transport phenomena. We demonstrate these effects in a highly-tunable class of recently synthesized two-dimensional kagome N-heterocyclic carbene (NHC) metal-organic frameworks. We showcase the controllability of the nonlinear effect upon applying external voltage, changing temperature, and chemical substitutions that preserve the bulk
topology and associated edge states. Our findings therefore reveal an uncharted presence of Euler class
topology in metal-organic materials that can be experimentally deduced through measurable magnetotransport.
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All authors Chun Wang Chau, Wojciech J. Jankowski, Bo Peng, Robert-Jan Slager
Materials Science
Structure Prediction and Bonding Analysis of B$_{18}$Ag$_2$ Clusters Featuring Double-Ring Motifs
Peter Ludwig Rodríguez-Kessler
The structural stability, electronic structure, and bonding characteristics of the silver-doped boron cluster B18Ag2 were investigated using density functional theory (DFT) combined with global optimization techniques. Basin-hopping searches identify a bent double-ring structure as the global minimum, consisting of two stacked B9 rings symmetrically stabilized by Ag atoms located above and below the boron framework. The UV-Vis absorption spectrum exhibits weak transitions in the near-infrared region and intense bands in the visible and near-ultraviolet regions, reflecting delocalized electronic excitations within the boron framework. Charge analysis indicates moderate electron redistribution from Ag atoms to the boron scaffold. Real-space bonding analyses based on the electron localization function (ELF), reduced density gradient (RDG), and molecular electrostatic potential (MEP) reveal that bonding is dominated by {$\sigma$}-delocalization over the boron skeleton, while Ag-B interactions are weak, non-directional, and primarily electrostatic. The continuous annular electron delocalization within the double-ring structure suggests an aromatic-like character. These findings establish B18Ag2 as a silver-stabilized boron double-ring cluster in which global electron delocalization governs structural stability, while Ag atoms act as axial stabilizing centers that modulate the electronic structure. This work provides new insight into the role of coinage-metal doping in stabilizing extended boron nanostructures.
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Materials Science
Global DIC-based sample-detector geometry refinement for accurate EBSD indexing
Claire Griesbach and Dennis M. Kochmann
Electron backscatter diffraction is a powerful tool for mapping crystallographic microstructures. However, the primary crux to improving orientation accuracy and applying the technique to challenging materials lies in the correct calibration of the sample-detector geometry. Many approaches have aimed at overcoming this barrier through various pattern center calibration strategies, but the pattern center only defines part of the sample-detector geometry. Here, we present a DIC-based geometry refinement method that obtains a single map-consistent sample-detector geometry, refining both the pattern center and sample/detector angles. We effectively decouple the local orientation changes from the global geometry effects on the Kikuchi patterns by calculating the consistent map-wide simulated-to-experimental pattern shifts associated with global geometry parameter errors. Using single-
crystal silicon and barium titanate (a material possessing six pseudosymmetric variants) as model materials, we demonstrate improved map-wide orientation consistency and more robust discrimination of pseudosymmetric variants than the Nelder-Mead and Differential
Evolution optimization strategies.
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Materials Science · Cross-listed from cond-mat.supr-con
Bragg-Williams order competes with superconductivity
Xu Liu, Xu Chen, Chuizhen Chen et al. (+14 more)
Orderings in charge and
spin have been extensively studied to unravel their correlation to emergent superconductivity over the past decades. Bragg-Williams order (BWO), a classical structural order parameter describing site occupancy in
alloys, has long been speculated to influence superconducting behavior. Yet, its role still remains ambiguous, largely due to the difficulty of isolating BWO from concomitant charge doping or competing electronic instabilities. Here, we establish In2/3PSe3 as a platform wherein indium vacancies are reversibly configurable between ordered and disordered states via thermal treatment. We show that the disordered phase undergoes a pressure-induced superconducting transition with a Tc of 11 K, significantly higher than the 7 K observed in its ordered counterpart. This constitutes a rare instance in which pure BWO variation drives a substantial shift in Tc. By combining a Ginzburg-Landau phenomenological analysis with a BCS-McMillan microscopic description, we demonstrate that BWO naturally suppresses superconductivity through electron-
phonon interactions, a mechanism supported by ultra-low-wavenumber Raman measurements. Our findings support BWO as an independent order parameter that competes directly with superconductivity, extending the concept of competing orders beyond conventional electronic and
magnetic degrees of freedom.
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All authors Xu Liu, Xu Chen, Chuizhen Chen, Boqin Song, Jing Chen, Xijing Dai, Qinghua Zhang, Feng Jin, Xingya Wang, Weiwei Dong, Dongliang Yang, Gefei Li, Pengju Zhang, Jiangping Hu, Jian-gang Guo, Tianping Ying, Xiaolong Chen
Materials Science
Predicting challenging phase transitions with Bayesian active learning
Lorenzo Bastonero, Gabriel Joalland, Chiara Cignarella et al. (+2 more)
Materials underpin modern technologies, from energy harvesting, storage, and conversion to information and communication technologies. Their functionality is often governed by the interplay between competing phases, as thermodynamic behavior shapes microscopic properties and ultimately determines technological performance; for instance, the light absorption of inorganic metal-halide perovskites in
solar cells. Accurately predicting
crystal thermodynamics, however, remains a major challenge for computational approaches because strong anharmonic effects require extensive sampling of the potential energy surface. Here, we present an on-the-fly
Bayesian framework, combined with the
stochastic self-consistent harmonic approximation, for learning first-principles interatomic potentials. This approach enables the prediction of thermodynamic properties over a broad temperature range with first-principles accuracy while requiring training on only a few tens to a few hundreds of atomic configurations. To demonstrate its power, we investigate the thermodynamic and dynamical properties of Li$_2$O, $\alpha$-CsPbI$_3$, and $\delta$-CsPbI$_3$, requiring only 44, 256, and 50 total-energy calculations, respectively. Notably, we show that this framework accurately captures the phase diagram of CsPbI$_3$, which explains its spontaneous degradation into the non-absorbing yellow phase, predicting the transition temperature with remarkable accuracy and efficiency. More broadly, the method presented opens a novel route toward accelerated materials engineering under realistic conditions for a wide range of technologically relevant applications, including solid-state batteries, optoelectronic devices, and memristors.
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All authors Lorenzo Bastonero, Gabriel Joalland, Chiara Cignarella, Lorenzo Monacelli, Nicola Marzari
Materials Science
Chemical transformation of MgH2/V2O5 composite to Mg-V-O rock salt and its influence on the electrochemical Li conversion and hydrogen storage characteristics of MgH2
D. Pukazhselvan, Ihsan Caha, Francisco J.A. Loureiro et al. (+5 more)
This study investigates the lithium conversion behavior of a hydrogen storage material based on vanadium
oxide added magnesium hydride. To understand the chemical interaction between vanadium
oxide and magnesium hydride, detailed X ray diffraction and X ray photoelectron spectroscopy analyses were performed on ball milled composites with varying compositions. The results confirm the formation of a combined magnesium vanadium
oxide with a rock salt structure, indicating strong chemical interaction between the components. It is further shown that the presence of a small amount of this
oxide additive significantly influences the lithium reaction with magnesium hydride, leading to a high initial discharge capacity and limited recharge capacity in lithium ion coin
cells. Post use analyses confirm the presence of magnesium hydride, suggesting that volume expansion is not responsible for the observed irreversibility. Electrochemical impedance spectroscopy using differential function of relaxation times indicates that electrolyte degradation is not a major issue. Instead, slow charge transfer processes are identified as the limiting factor, and these are sensitive to the composition of the additive. These findings highlight that improving electrode and electrolyte compatibility is essential for enhancing performance in this system.
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All authors D. Pukazhselvan, Ihsan Caha, Francisco J.A. Loureiro, Francis Leonard Deepak, Catarina de Lemos, Aliaksandr L. Shaula, Sergey M. Mikhalev, Duncan Paul Fagg
Materials Science · Cross-listed from cond-mat.str-el
Validity of DFT+U band gaps in all its known functional forms
Andrew C. Burgess and David D. O'Regan
The Density Functional Theory plus Hubbard U (DFT+U) technique is one of the most widely used tools by condensed matter physicists and solid state chemists for the simulation of transition-metal and lanthanide bearing
crystals, and increasingly of much more diverse chemistries... Since the earliest days, the gap in the DFT+U single-particle eigenspectrum has been associated with the fundamental band gap, and the method has typically found more success for spectra than for total-energy derived properties. There has been some doubt, however, as to the conceptual validity of this association. Here, extending findings from recent years regarding local, semi-local, and hybrid functionals within the generalized Kohn-Sham framework, we prove and numerically demonstrate that the DFT+U eigenspectrum gap is conceptually valid, in the specific sense that it matches its own fundamental gap calculated using total-energy differences. We emphasize that this does not imply its agreement with experimental values, and indeed our argument is independent of the Hubbard U parameter. The result holds for pristine periodic systems with converged k-point sampling but not, however, for defective ones, isolated systems, or systems in which added charges exhibit spontaneous localization. We show that bandgap validity for pristine solids holds in the presence of pseudopotentials and PAW potentials, when using hybrid functionals, and in DFT+U(+J) irrespective of the level of subspace projection onto the band-edge states. We survey every collinear-
spin DFT+U-type functional known to have been published to date, within a unified notation... Returning to the related but different question of band-gap correction efficiency, we offer fresh analysis of DFT+U bandgap projection dependence, and each functional's effect on energies and gaps for the hydrogen
lattice in the Mott-Hubbard limit.
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Materials Science
Spin-Axis-Layer Locking for Intrinsic Bipolar Altermagnetic Semiconductors: Proof-of-Concept in Bilayer CuBr2
Wei Ma, Dengpan Ma, Zhiheng Lv et al. (+1 more)
Electrical control of
spin and
magnetic sublattice degrees of freedom is essential for multifunctional and low-power spintronic devices. Bipolar altermagnetic
semiconductors (BAMSs)-characterized by opposite
spin polarizations at the valence and conduction band edges-offer such control, yet known systems require external strain and sizable valley polarization for gate-tunable switching. Here, we propose a universal
spin-axis-layer locking (SALL) paradigm to overcome these limitations. By stacking two quasi-1D
ferromagnetic monolayers with a 90 degrees twist, the
bilayer reconstructs altermagnetic
symmetry, yielding an intrinsic BAMS state where carrier
spin is locked to specific layers and transport directions. Using synthesized CuBr2 monolayers as proof-of-concept, we demonstrate via first-principles calculations a robust BAMS state. Electrostatic gating enables simultaneous, reversible switching of carrier type,
spin, and active layer, generating fully
spin-polarized axial charge currents and directionally controllable pure
spin currents with near-unity charge-to-
spin conversion efficiency. This SALL model establishes a versatile, strain-independent strategy for advanced all-electrical altermagnetic devices.
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All authors Wei Ma, Dengpan Ma, Zhiheng Lv, Zhifeng Liu
Materials Science · Cross-listed from physics.optics
Thermo-optic dynamics of effective epsilon-near-zero media
Jiaye Wu, Xuanyi Liu, Marco Clementi et al. (+4 more)
Epsilon-near-zero (ENZ) photonic media exhibit extreme optical dispersion that enables unconventional light-matter interactions and enhanced optical nonlinearities. Recent studies suggested that thermo-optic effects, traditionally regarded as slow and secondary, can be strongly modified under the ENZ condition. Here we establish thermo-optic reconfiguration of effective media as a unified physical framework to describe both static and transient thermo-optic phenomena in ENZ systems. Using a CMOS-compatible effective medium operating in the visible spectral range, we experimentally demonstrate that temperature variation, whether under thermal
equilibrium or transient excitation, reconfigures the constitutive parameters defining the ENZ condition, giving rise to pronounced linear and nonlinear optical responses. At thermal
equilibrium, this reconfiguration manifests itself as static ENZ wavelength shift with an unprecedentedly large thermal-spectral modulation rate and an effective thermo-optic coefficient on the order of $10^{-1}$ K$^{-1}$. Under ultrafast excitation, we observe a picosecond-scale thermo-optic nonlinear response induced by transient heating. This response can be consistently interpreted as a time-dependent reconfiguration of the effective ENZ medium, corresponding to a transient
evolution of its optical parameters. By reframing thermo-optic effects as a process of static and dynamic reconfiguration of effective media, this work provides a unified perspective that bridges thermo-optic physics, effective-medium theory, and time-varying photonics.
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All authors Jiaye Wu, Xuanyi Liu, Marco Clementi, Shuang Qiu, Limin Lin, Zhang-Kai Zhou, Camille-Sophie Brès
Materials Science · Cross-listed from cond-mat.str-el
Collective and separate metal-insulator transitions in correlated vanadium dioxide
Xuanchi Zhou, Xiaohui Yao, Wentian Lu et al. (+2 more)
Deciphering the complicated interplay between collective and separate behaviors lies at the heart of first-order metal-
insulator transition (MIT) in correlated electron systems, enabling the rational design of exotic electronic states and functionalities. The critical balance between collective and separate behaviors defines a fundamental collective length scale, typically shorter than 5 nm, that governs emergent
quantum orders, yet active control over this dichotomy remains elusive. Here, we realize on-demand manipulation of the collective and separate MIT within the correlated VO2 system in a reversible fashion. Artificially designing the oxygen deficiency in VO2/VO2-x homojunction fosters a collective MIT with an extended collective length scale, whereas the introduction of a TiO2 interlayer drives a crossover from this collective to a two-step separate MIT via decoupling of the electronic order parameter. Incorporating mobile hydrogens into the VO2/TiO2/VO2-x trilayer enables reversible control over electronic phase modulations, transitioning a two-step MIT towards either a one-step MIT or collective electron localization. This ionic control over the electronic band structure of VO2 flexibly triggers multi-state MIT, a process governed by hydrogen-related band filling. Our findings transform the collective length scale from a passive threshold into a dynamic design parameter, establishing a viable handle for engineering collective and separate MIT for adaptive correlated electronics.
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All authors Xuanchi Zhou, Xiaohui Yao, Wentian Lu, Chunwei Yao, Xiaomei Qiao
Materials Science · Cross-listed from cond-mat.mes-hall
Binary topological logic gates in Kane-Mele nanostructures via local control of edge-state transport
K. Zberecki
Topological edge states offer a promising basis for post-CMOS device concepts. However, their use in elementary logic requires simple and physically transparent architectures. Here we study binary logic in Kane-Mele nanostructures with spatially localized control regions. Logical inputs are encoded by local electrostatic, exchange-like, and Rashba-type perturbations. The output is read from terminal transmission within the Landauer-Buttiker framework. We demonstrate working NOT and AND gates in multiterminal honeycomb geometries. Real-space current maps show that their operation is governed by controlled rerouting of edge currents rather than by finely tuned interference. Both gates reproduce the complete truth table in all 50 Anderson-disorder realizations at each tested disorder strength up to W/t=0.1. The NOT gate also remains correctly classified at all 441 points of a two-parameter control scan.
Geometric tests confirm stable operation for several patch lengths and branch widths. These results establish Kane-Mele nanostructures as a transparent and numerically robust platform for primitive topological binary logic.
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Materials Science
Physical properties of transition metal hydride superconductors Mg2TmH6 (Tm = Rh, Pd, Ir, Pt) by first-principles calculations
Md Ashraful Alam, Md Abdul Hadi Shah, F. Parvin et al. (+1 more)
In this work, a comprehensive first-principles investigation of the structural, hydrogen storage potential, electronic, elastic, mechanical, thermophysical, superconducting, and optical properties of Mg2TmH6 (Tm = Rh, Pd, Ir, Pt) hydrides is presented. Obtained results demonstrate that Mg2TmH6 hydrides combine favorable hydrogen storage, mechanical robustness, superconductivity, and multifunctional optical properties, making them promising candidates for energy storage, superconducting and advanced optoelectronic applications.
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All authors Md Ashraful Alam, Md Abdul Hadi Shah, F. Parvin, S. H. Naqib
Materials Science
Substitutional platinum as an efficient nonradiative recombination center in silicon
Zhenxing Dai, Menglin Huang, Xin-Gao Gong et al. (+1 more)
Platinum (Pt) is widely used for carrier-lifetime control in silicon power devices, yet the microscopic nonradiative recombination mechanism of the substitutional platinum ($\text{Pt}_\text{Si}$) dopant remains debated. Using first-principles calculations combined with nonradiative multiphonon theory, we systematically investigate the electronic structures and carrier capture dynamics of $\text{Pt}_\text{Si}$. Our results show that both the donor ($+/0$) and acceptor ($0/-$) levels of $\text{Pt}_\text{Si}$ exhibit large capture cross sections for electron and hole carriers, thereby making $\text{Pt}_\text{Si}$ an effective recombination center. Notably, the calculated capture cross sections are sensitive to the
symmetry-equivalent defect configurations with different Jahn-Teller distortions. By accounting for two different $D_{2d}$ configurations of neutral $\text{Pt}_\text{Si}$ during transitions properly, our calculated carrier capture cross sections align well with experimental values. This work provides a microscopic picture of the carrier capture processes induced by $\text{Pt}_\text{Si}$ and emphasizes the importance of
symmetry-equivalent configurations in defect-assisted nonradiative recombination.
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All authors Zhenxing Dai, Menglin Huang, Xin-Gao Gong, Shiyou Chen
Materials Science · Cross-listed from cond-mat.str-el
Observation and Control of Moiré-Tailored Topological Dirac States
R. Ganser, M. P. T. Masilamani, B. Geldiyev et al. (+6 more)
Moiré
heterostructures provide a powerful framework for tailoring electronic band structures via controlled long-range periodic superlattice potentials. Beyond widely studied moiré-tailored flat bands, folded band structures can host emergent Dirac states, which have recently attracted considerable interest. Direct momentum-resolved observation of gapless moiré-Dirac quasiparticles, however, is challenging and has so far remained elusive. By performing angle-resolved photoemission spectroscopy measurements on an epitaxial surface-moiré structure, we here provide direct spectroscopic evidence of moiré-dressed Dirac states with topological character. Driven by the one-dimensional superlattice potential, electrons propagate anisotropically with a weak but massless Dirac dispersion along the confinement direction. The observed band crossings belong to topological nodal lines pinned to the mini-Brillouin zone boundaries. As such, they are enforced and robustly protected by the non-symmorphic
symmetry of the superlattice. Finally, we demonstrate that the topological excitations can be almost continuously controlled by tuning the moiré
lattice periodicity, directly unveiling moiré
heterostructures as a promising platform for creating and controlling topological moiré-Dirac states.
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All authors R. Ganser, M. P. T. Masilamani, B. Geldiyev, M. M. Hirschmann, A. Consiglio, J. Schusser, D. Di Sante, M. Ünzelmann, F. Reinert
Materials Science · Cross-listed from cond-mat.mes-hall
Magnomechanical Coupling in Suspended 2D van der Waals Ferromagnets
Ritesh Das, Alvaro Bermejillo-Seco, Herre S. J. van der Zant et al. (+2 more)
Magnomechanical systems provide a promising route for exploring coherent hybrid
magnon-
phonon interactions and hybrid information processing, but their realization has so far been limited by weak
magnon-
phonon coupling in conventional bulk platforms. We show that a suspended membrane of a two-dimensional van der Waals ferromagnet with in-plane magnetization and out-of-plane mechanical oscillations exhibits large magnomechanical coupling dominated by magnetoelastic interactions. The parametric single
magnon-
phonon coupling rate scales linearly with pre-strain and can reach hundreds of Hertz to low kiloHertz in suspended membranes of van der Waals ferromagnets such as CrGeTe_3 under experimentally realistic conditions. This rate exceeds typical values reported for YIG spheres by more than three orders of magnitude. Our results demonstrate that suspended membranes of van der Waals magnets provide a robust and highly tunable platform for magnomechanics.
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All authors Ritesh Das, Alvaro Bermejillo-Seco, Herre S. J. van der Zant, Peter G. Steeneken, Yaroslav M. Blanter
Materials Science
Tuning magnitude and direction of lattice thermal conductivity in transition metal dichalcogenide heterobilayers
Elliot Perviz and Antonio Cammarata
We investigate the nanoscale mechanisms determining
lattice thermal conductivity (LTC) of pristine and W-doped MX$_2$-M$^\prime$X$^\prime_2$ transition metal dichalcogenide heterobilayers from first principles, using the exact solution of the linearised Boltzmann transport equation in both
phonon and relaxon bases. Pristine heterobilayers exhibit isotropic in-plane LTC with preserved ordering across temperature. Relaxon analysis identifies descriptors linking LTC to
phonon properties such as the
phonon group velocity and layer localisation. While systems with lighter atoms generally favour higher LTC, a sufficiently large mass contrast is required to induce layer localisation of the transport-relevant vibrational modes. Further, we show through the thermal viscosity that the relative distribution of vibrational states between metal/non-metal sublattices influences the balance between Normal and Umklapp scattering processes. On the other hand, doped systems exhibit reduced and anisotropic in-plane LTC, retain a well-defined layer character, but are strongly affected by enhanced
phonon-
phonon scattering due to mass disorder. Notably, we find that both configuration and temperature dictate the direction of maximum thermal transport, which opens the possibility to tune the direction of maximum (and minimum) conductivity via doping in novel 2D functional materials. Thanks to its general formulation, the analysis protocol can be readily extended to other van der Waals
heterostructures, and the descriptors may be implemented in high-throughput engines to identify promising layered materials with tailored thermal transport characteristics.
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Materials Science · Cross-listed from cond-mat.str-el
Topochemical Fluorination of La$_2$NiO$_{4+\delta}$ Single Crystals
Hasan Yilmaz, Masahiko Isobe, Oliver Clemens et al. (+1 more)
Topochemical fluorination offers a low–temperature route for modifying the anion chemistry and electronic ground states of layered transition-metal
oxides, providing access to metastable phases and functionalities that are not able to be achieved through conventional solid–state synthesis. Despite extensive work on polycrystalline samples and thin films, topochemical fluorination of bulk single
crystals has not been studied, limiting insights into intrinsic structure property relationships. Here, we investigate the topochemical fluorination of optical float zone grown (OFZ) La$_2$NiO$_{4+\delta}$ single
crystals using
polymer-based PTFE, PVDF and inorganic CuF$_{2}$ fluorination
agents and compare it to our topochemical pathways of reduction of LaNiO$_{3-x}$. By systematically investigating direct and indirect contact reaction pathways, we can understand fluorination mechanisms, quantify the degree of fluorine incorporation, and evaluate the resulting structural and
magnetic modifications in a detail that was not possible in powder and thin films. Powder and single–
crystal X-ray diffraction reveal that fluorination proceeds without destroying the Ruddlesden–Popper framework, while inducing
lattice parameter changes consistent with anion intercalation in the bulk and ion exchange on the surface. This even induces a clear superstructure, which was not reported before and extends the understanding of anion insertion reactions beyond what is known on stage ordering in nickelates. Energy-dispersive X–ray spectroscopy confirms strong fluorine incorporation on the surface and reduced homogeneity in the bulk.
Magnetic susceptibility measurements demonstrate a change in
antiferromagnetic ordering upon fluorination.
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All authors Hasan Yilmaz, Masahiko Isobe, Oliver Clemens, Pascal Puphal
Materials Science
Benchmarking bandgap prediction in semiconductors under experimental and realistic evaluation settings
Haolin Wang, Xianyuan Liu, Anna Jungbluth et al. (+3 more)
Accurate bandgap prediction is crucial for
semiconductor applications, yet machine learning models trained on computational data often struggle to generalize to experimental bandgap measurements. Challenges related to data fidelity, domain generalization, and model interpretability remain insufficiently addressed in existing evaluation frameworks. To bridge this gap, we introduce RealMat-BaG, a
benchmark for assessing model reliability under experimentally relevant conditions. We curate an open-access
dataset of experimental bandgaps with aligned
crystal structures and compare graph neural networks as well as classical machine learning baselines. Our framework evaluates performance across statistical and domain-based splits, examines transfer from DFT-computed to experimental bandgaps, and analyzes interpretability at both elemental-property and structural levels. Our results reveal the fundamental generalization limitations of current bandgap prediction models and establish a
benchmark aligned with experimental measurements for developing more reliable learning strategies for materials discovery.
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All authors Haolin Wang, Xianyuan Liu, Anna Jungbluth, Alexandra J. Ramadan, Robert D. J. Oliver, Haiping Lu
Materials Science · Cross-listed from cond-mat.mes-hall
Doping-Induced Brightening of Dark Excitons and Trions in a WSe$_2$ Monolayer
Grzegorz Krasucki, Artur O. Slobodeniuk, Kacper Walczyk et al. (+5 more)
Optically dark excitonic states play a critical role in the valleytronic, electronic, and optical properties of monolayer semiconducting transition metal dichalcogenides. Here, we investigate how electrostatic doping affects the in-plane
magnetic-field-induced activation of dark excitonic complexes in a gated WSe$_2$ monolayer. By continuously tuning the carrier density via gate voltage, we access $n$-type, charge-neutral, and $p$-type regimes and track the corresponding brightening dynamics. We find that the brightening rates of the dark negative trion ($T^{D-}$), dark neutral
exciton ($X^{D}$), and dark positive trion ($T^{D+}$) exhibit a strong and nontrivial dependence on doping. In particular, the pronounced asymmetry in the brightening behaviour of the neutral $X^{D}$ complex and the charged $T^{D-}$ and $T^{D+}$ trions reveals distinct underlying carrier interactions, which we describe using a rate-equation model for their steady-state populations. These findings highlight the key role of dark excitonic complexes in governing the optical response and carrier dynamics of doped S-TMD monolayers.
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All authors Grzegorz Krasucki, Artur O. Slobodeniuk, Kacper Walczyk, Katarzyna Olkowska-Pucko, Kenji Watanabe, Takashi Taniguchi, Adam Babiński, Maciej R. Molas
Materials Science
Electronic structures of spin-orbit-coupled metal candidate PbRe$_2$O$_6$: one dimensionality and molecular orbital formation
Yuki Yanagi and Michi-To Suzuki
We present a first-principles investigation of the electronic structure of the inversion-
symmetry-broken
spin-orbit-coupled metal candidate PbRe$_2$O$_6$. Our calculations reveal that the
Fermi surfaces derived from the $d_{yz}$ and $d_{zx}$ orbitals exhibit pronounced one-dimensional characteristics, which naturally account for the highly anisotropic charge transport observed experimentally. In addition, the $d_{x^2-y^2}$ orbitals on each Re haxagon form molecular orbitals, where the resulting $E_g$ molecular states generate nearly dispersionless bands in close proximity to the
Fermi level. The coexistence of these quasi-1D
Fermi surfaces and molecular-orbital-induced flat bands provides a possible microscopic origin for the successive phase transitions observed in PbRe$_2$O$_6$.
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Materials Science · Cross-listed from cond-mat.soft
Fundamental picture of the conduction mechanism in solid-state polymer electrolytes revealed by terahertz spectroscopy
Johanna Weidelt, Jijeesh Ravi Nair, Diddo Diddens et al. (+9 more)
Solid
polymer electrolytes (SPEs) based on cross-linked poly(ethylene
oxide) (PEO) encompassing lithium salts have gained significant
attention as separators in solid-state lithium metal batteries. Here, we employ terahertz time-domain spectroscopy (THz-TDS), as a noninvasive contact-free technique, to investigate the conduction properties of these cross-linked SPEs and unravel their dependencies on the added lithium salt and the sample temperature. The obtained THz conductivity spectra are dominated by THz absorption bands, which we attribute to resonant vibrations within the
polymer matrix of the electrolyte. By careful application of Lorentz model, the conductivity spectra have been analyzed, and the relevant
polymer vibration modes have been quantitatively assessed. Calculations based on the density functional theory (DFT) were performed to elucidate the possible microscopic mechanisms of these resonant vibrations. This study sheds light on the relevance of
polymer matrix vibrations validating the hopping transport of lithium ions in SPEs which ultimately leads to the technologically relevant ionic conduction in the solid-state
polymer-based electrolytes.
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All authors Johanna Weidelt, Jijeesh Ravi Nair, Diddo Diddens, Wentao Zhang, Felix Pfeiffer, Tiago de Oliveira Schneider, Markus Meinert, Tomoki Hiraoka, Linda Nesterov, Masoud Baghernejad, Dmitry Turchinovich, Hassan A. Hafez
Materials Science
Probing sliding ferroelectricity in bilayer T$_\mathrm{d}$-WTe$_2$ with high-harmonic generation
Elias Greil, Alba de las Heras, Angel Rubio et al. (+1 more)
High-harmonic generation is a sensitive all-optical probe of
symmetry and electron dynamics in solids. Here, we use first-principles time-dependent density functional theory (TDDFT) to study high-harmonic generation in T$_d$-WTe$_2$, a two-dimensional semimetal with switchable out-of-plane ferroelectric polarization driven by interlayer sliding. We show that the mirror-
symmetry breaking underlying the ferroelectric state produces robust signatures in polarization-resolved high-harmonic spectra, enabling optical identification of the polarization state. By incorporating interlayer shear motion in coupled electron-
lattice TDDFT simulations, we further show that the 0.24 THz shear mode is slow enough to remain effectively decoupled from the ultrafast electronic response responsible for harmonic emission. Our results establish high-harmonic spectroscopy as a non-invasive probe of sliding ferroelectricity and
lattice symmetry in two-dimensional
quantum materials.
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All authors Elias Greil, Alba de las Heras, Angel Rubio, Anna Galler
Materials Science
Rethinking the Role of Homogeneous Surface Models in High-Entropy Alloy Catalyst Screening
Jin-Soo Kim, Taegyeong Kim, Youngtak Kim et al. (+2 more)
High-
entropy alloy (HEA) catalysts are commonly modeled as homogeneously mixed surfaces, although thermodynamic driving forces can produce surface segregation and chemical ordering. Here, we test the validity and practical limits of this approximation by comparing random homogeneous slabs with surfaces annealed using cluster-expansion Monte Carlo (CEMC) against three published high-throughput composition-activity
datasets for the oxygen reduction and hydrogen
evolution reactions. Monte Carlo-based uncertainty quantification simulations propagated uncertainties in catalyst composition and predicted binding energies through 10,000 trials. CEMC generally improved agreement with experiment, but the advantage is not robust, and neither model reliably reproduces experimental composition-activity map. Structural analysis revealed surface segregation, rather than short-range ordering, is the primary origin of the difference between the models. Nevertheless, the element-conditioned binding-energy ranges of the two models largely overlapped, supporting the use of homogeneous slabs for rapid screening of elemental combinations.
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All authors Jin-Soo Kim, Taegyeong Kim, Youngtak Kim, Sathya Sheela Subramanian, Geun Ho Gu