Materials Science · Cross-listed from cs.LG
Unraveling the Size Determination Mechanism of Nanocrystal Synthesis via Interpretable Neural Networks
Kai Gu and Haizheng Zhong
Deep learning models of nanocrystal synthesis enable the prediction of size and shape by encoding precursors and reaction conditions. However, their black-box nature hinders gaining deep insights into the underlying synthetic mechanisms. Here, we develop the Nanocrystal Equation Learner (NanoEQL), a fully white-box neural network to unravel the size determination mechanisms of nanocrystal synthesis. Building on the EQL architecture, eight operators are introduced to replace standard activation functions to fit the mathematical equations in nanocrystal synthesis. Among these operators, three smoothed operators address the gradient explosion of singular operators at zero. To evaluate the weights of different precursors, we develop a temperature-gated
attention pooling strategy that encodes concentration-driven and reactivity-driven chemical synthesis mechanisms into the temperature gate. The NanoEQL model illustrates that the final nanocrystal size can be described by a linear equation composed of three scalars representing nanocrystallization capability (-Zp), growth capability (Zrea), and external input potential (-Zops). These interpretable scalars not only advance the rational design of nanocrystal synthesis but also establish a generalizable paradigm for deciphering chemical reaction mechanisms through white-box machine learning.
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Materials Science
Autferroics-based true random number generators with enhanced performance
Jun-Jie Zhang, Shuai Dong and Boris I. Yakobson
Physical
entropy-driven true random number generators are essential for emerging probabilistic computing paradigms, but conventional implementations based on
magnetic tunneling junctions have reached their performance plateaus limited by inherent tradeoffs and weak tunability. Here, autferroics, a sister branch of multiferroics, is proposed to construct true random number generators. Benefiting from its unique energy landscape due to strong seesaw-type magnetoelectricity, the performance of true random number generation can be significantly enhanced in autferroic tunneling junctions, verified by passing standard statistical tests. Furthermore, autferroics-based random number generators can exhibit multi-field tunability and intrinsic multi-state randomness, opening an avenue for efficient hardware realization of the complex-number arithmetic and simulation of probability distributions of
quantum mixed states within
stochastic circuits.
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Materials Science
Realizing record-high transverse thermoelectric figure of merit at room temperature in artificially tilted multilayers based on high power factor NiFe alloy
Yebin Lee, Fuyuki Ando, Takamasa Hirai et al. (+3 more)
Transverse thermoelectric conversion using artificially tilted multilayers (ATMLs) offers a versatile device architecture that circumvents the structural limitations of conventional longitudinal thermoelectrics. However, achieving competitive room-temperature thermoelectric performance without an external
magnetic field remains a critical challenge. Here, we report a record-high transverse thermoelectric figure of merit $z_{yx}T$ of 0.36 in Ni$_{50}$Fe$_{50}$/Bi$_{0.2}$Sb$_{1.8}$Te$_{3}$-based ATML at room temperature without an external
magnetic field. Leveraging the longitudinal high power factor in a Ni$_{50}$Fe$_{50}$
alloy and the sharp contrast in electrical and thermal transport properties between $n$-type Ni$_{50}$Fe$_{50}$ and $p$-type Bi$_{0.2}$Sb$_{1.8}$Te$_{3}$, we engineer an anisotropic structure that simultaneously exploits high electrical conductivity, large transverse thermopower, and low thermal conductivity to maximize $z_{yx}T$ in ATML. Through the direct measurements of these thermoelectric transport parameters, we obtained $z_{yx}T$ of 0.36 in Ni$_{50}$Fe$_{50}$/Bi$_{0.2}$Sb$_{1.8}$Te$_{3}$-based ATML, which is in excellent agreement with the analytical prediction of 0.36 owing to the low interfacial electrical and thermal resistances at the Ni$_{50}$Fe$_{50}$/Bi$_{0.2}$Sb$_{1.8}$Te$_{3}$ junctions. These results pave the way for the practical implementation of transverse thermoelectric materials around room temperature.
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All authors Yebin Lee, Fuyuki Ando, Takamasa Hirai, Keisuke Hirata, Kota Hasegawa, Ken-ichi Uchida
Materials Science
SPEAR: Structure Property Explainability with Attention Regularization
Aditya Raghavan, Utkarsh Pratiush, Dalton A. Pearl et al. (+4 more)
Machine learning is increasingly used to learn structure property relationships from spectroscopic and diffraction data, yet its adoption in materials discovery is often limited by poor interpretability of model predictions. Although
attention mechanisms are frequently treated as inherently explainable, unregularized
attention can yield unstable, fragmented, or intensity driven attribution patterns that obscure the physical origin of these relationships. Here we introduce SPEAR (Structure Property Explainability with
Attention Regularization), a framework that constrains
attention distributions during training to improve their stability, selectivity, and physical interpretability. SPEAR augments
attention based regression with a learnable temperature that controls
attention concentration and a smoothness penalty that enforces coherence across neighboring spectral positions, treating
attention as a learnable explanatory object rather than a post hoc visualization. Using synthetic spectral
benchmarks with known generative structure, we show that
attention regularization produces smooth, contiguous attribution profiles aligned with causal features while preserving predictive accuracy. Applied to experimental X ray diffraction data from a combinatorial rare earth zirconate thin film library, the regularized model selectively emphasizes physically relevant diffraction features and decouples feature importance from raw peak intensity. The reflection it identified prompted a reassessment of our earlier structural analysis, revealing a correlation between the 220 peak position, the tetragonal distortion that accommodates cation size disorder, and the local thermal conductivity.
Attention regularization therefore provides a principled training constraint for explainable structure property regression, yielding mechanistically meaningful explanations without sacrificing predictive performance.
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All authors Aditya Raghavan, Utkarsh Pratiush, Dalton A. Pearl, Jade Holliman Jr, Katharine Page, Philip D Rack, Sergei V Kalinin
Materials Science
Multiscale Correlation of Morphological, Chemical, and Optical Properties in p-Type Porous Silicon
Arturo Ramírez-Porras and Isaac Prado-Bermúdez
We report a systematic study of the correlations among electrochemical processing conditions and the morphological, chemical, and optical properties of porous silicon (pSi). Twenty pSi samples were fabricated from boron-doped (100) crystalline silicon by varying current density, etching time, and hydrofluoric-acid concentration. Scanning electron microscopy,
Fourier-transform infrared spectroscopy, and photoluminescence were used to characterize the resulting structures. The two-dimensional porosity varied only moderately, whereas porous-layer thickness increased with etching time and current density. The silicon oxide to silicon hydride ratio showed comparatively small variations. Corrected photoluminescence spectra were fitted with a four-component
quantum-wire/
quantum-dot model including localized surface-state transitions. The extracted
quantum-wire and
quantum-dot dimensions decreased systematically with increasing current density, while the photoluminescence maximum under 375 nm excitation showed no clear monotonic dependence on processing conditions. The results demonstrate that no single descriptor adequately captures the multiscale behavior of porous silicon.
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Materials Science
Defect-controlled twin activation in crystallographically equivalent magnesium micropillars
Hexin Wang, Fatim Zahra Mouhib, Chunhua Tian et al. (+6 more)
Tensile twinning plays a central role in accommodating <c>-axis plasticity in Mg. In bulk Mg, it typically shows a relatively deterministic response with a low critical stress, whereas in confined volumes it exhibits broad yield-stress distributions that complicate the prediction of small-scale mechanical behavior. Here, site-specific compression tests are performed on 4 $\mu$m-diameter pillars fabricated in a parent Mg
crystal and an adjacent {10-12} twin. The two regions share the same [11-20] compression axis but experienced different prior deformation histories, allowing the influence of the residual microstructural state to be examined at fixed crystallographic orientation. Among 27 pillars, most parent-region pillars yield near 300 MPa, whereas pillars from the twin region span approximately 30 to 300 MPa. Interrupted tests combined with cross-sectional EBSD link individual load drops to discrete twin formation and further show that a pillar containing a pre-existing twin yields at approximately 80 MPa through the migration of the existing twin boundary. Molecular dynamics simulations of 30 nm-diameter pillars resolve possible atomistic pathways at the nanoscale. The simulations illustrate how contact geometry and pre-existing twin embryos alter event selection, and how an activated twin advances rapidly, while coherent twin boundary migration proceeds through disconnection motion accompanied by crystallographically required atomic shuffles. The results attribute the experimental scatter to the local availability of embryos and mobile interfaces, such that the first plastic event is governed by the twinning pathway accessible from the local microstructural state rather than by a single characteristic critical stress. Deformation history can therefore strongly modify the distribution of first plastic events even when the loading orientation is fixed.
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All authors Hexin Wang, Fatim Zahra Mouhib, Chunhua Tian, Sang-Hyeok Lee, Henry Ovri, Julien Guénolé, Sandra Korte-Kerzel, Talal Al-Samman, Zhuocheng Xie
Materials Science
Thickness-dependent secondary-electron emission from suspended MoS$_2$ membranes in the helium ion microscope
Cyan Kim, David Lister, Philip Jackle et al. (+1 more)
Secondary-electron (SE) emission in the helium ion microscope (HIM) becomes sensitive to membrane thickness when the sample is thin enough for He-ion transmission and when the SEs emitted from the bottom surface are collected. We correlated the total SE intensity of suspended, nanometer-thick MoS$_2$ flakes on lacey carbon with thickness measured independently by electron energy-loss spectroscopy. The response peaks at 40-55 nm, with an apparent back-to-front SE signal ratio reaching 4.7. The peaked, thickness-dependent component is attributed primarily to SE emission at the bottom surface of the flake, rather than to transmitted ions striking instrument surfaces. Applying SRIM ionization profiles, an asymmetric SE-escape model with a longer escape depth on the exit side reproduces the response. We find an effective exit-side escape depth of approximately 10 nm, five times the assumed 2 nm entrance value, suggesting that deposited energy reaches the exit surface far more efficiently than the entrance surface or that the SRIM model's energy deposition profile is shifted by an effect such as channeling. The correlation provides a rapid thickness screen for suspended membranes and a route to testing low-energy ion-solid interaction models in thin materials.
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All authors Cyan Kim, David Lister, Philip Jackle, Karen L. Kavanagh
Materials Science · Cross-listed from physics.optics
All-optical switching of nonlinear structured light in crystal-engineered van der Waals materials
Paolo Valisa, Marc Richstaetter, Bianca Sanfilippo et al. (+9 more)
The orbital angular momentum (OAM) of light is a discrete, unbounded degree of freedom that underpins mode-multiplexed communications and high-dimensional
quantum photonics. Yet, dynamic OAM control remains dependent on bulky free-space optics or cascaded architectures that separate switching from wavefront shaping, hindering nanoscale integration. Here, we engineer artificial van der Waals
crystals from rhombohedrally stacked (3R) MoS$_2$, in which spatial control of the local
crystal orientation imprints a nonlinear
geometric phase onto the second-harmonic (SH) field, enabling background-free generation of SH
vortex beams in an ultrathin (46 nm) van der Waals platform. Leveraging the C$_{3v}$
symmetry of 3R-MoS$_2$, we demonstrate monolithic, all-optical switching with sub-optical-cycle precision between Hermite-Gauss-like and Laguerre-Gaussian
vortex SH beams with opposite topological charges ($l=\pm1$). Our results establish artificial 3R-MoS$_2$
crystals as a monolithic platform for the generation and all-optical reconfiguration of nonlinear structured light at the nanoscale, advancing active nanophotonic sources for integrated classical and
quantum photonic technologies.
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All authors Paolo Valisa, Marc Richstaetter, Bianca Sanfilippo, Benedikt Ursprung, Zhi Hao Peng, Victoria Quiros-Cordero, Francesco Gucci, Xiaoyang Zhu, P. James Schuck, Giulio Cerullo, Luca Carletti, Chiara Trovatello
Materials Science · Cross-listed from cond-mat.supr-con
Insight into SRF cavity performance from simulations of Nb's surface oxide dissolution and diffusion
Ryan M. L. McFadden, Rowan Becker and Tobias Junginger
We report simulations of the dissolution and
diffusion of Nb's surface oxide layer in
vacuum. While this chemical doping process is important for the surface preparation of Nb superconducting
radio frequency (SRF) cavities - common components of particle accelerators - quantitatively linking the resulting oxygen distributions to superconducting performance remains challenging. In this work, we simulate the reaction-
diffusion process numerically for treatment temperatures $T = 50^{\circ}$C to $200^{\circ}$C and times $t = 0.5$ h to $120$ h, and calculate the effect of the spatially inhomogeneous oxygen doping on Nb's superconducting properties. We find that oxygen doping redistributes the Meissner screening current, reducing its value at the surface and shifting its maximum several nanometres into the material. These results provide a microscopic link between oxygen
diffusion profiles and the electromagnetic response of Nb relevant for SRF cavity operation. This work provides a quantitative framework linking oxygen
diffusion profiles to superconducting performance and establishes a foundation for future studies involving time-dependent and multi-step heat treatment protocols.
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Materials Science
Landau theory and exchange instabilities in Mn$_5$Si$_3$: A case against strain-induced altermagnetism
K. D. Belashchenko
Thin-film Mn$_5$Si$_3$ is a prominent altermagnetic candidate owing to its
metallicity, demonstrated anisotropic anomalous transport, and proposed $d$-wave exchange splitting that could enable
spin-polarized transport. Its postulated altermagnetic structure has zero propagation vector, unlike the bulk collinear antiferromagnetic AFM2 phase, which orders at the $M$
star. We analyze both phases using Landau theory, first-principles paramagnetic-instability calculations, and Monte Carlo simulations. AFM2 appears in Landau theory as a
symmetry-protected inversion-even, permutation-odd mode at a single arm of the $M$
star. At $\Gamma$, the same intracell pattern belongs to the collinear sector of an $E_{2g}$ order parameter; both phases require higher-order terms for their selection. Disordered-local-moment calculations identify the leading exchange instability at $M$, and the resulting classical Heisenberg model orders at the bulk experimental temperature scale into the orthogonal $3M$ phase favored by single-site
entropy. Magnetostructural coupling to $E_{2g}$ deformations favors single-$M$ AFM2 ordering. The estimated homogeneous-strain contribution to the relevant quartic coefficient is about a quarter of the competing entropic term near the bulk transition, while internal $E_{2g}$ relaxations are expected to provide additional stabilization. The $\Gamma$-point $E_{2g}$ mode, whose Landau theory contains the altermagnetic sector, is substantially weaker and further suppressed by epitaxial strain comparable to that reported for Mn$_5$Si$_3$/Si(111) films exhibiting anomalous transport. The same strain reduces the leading
magnetic exchange scale. These results explain the bulk $M$-point instability but strongly disfavor relocating the propagation vector from $M$ to $\Gamma$ in a moderately strained bulklike Mn$_5$Si$_3$ film, leaving the identity of the Hall-active phase unresolved.
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Materials Science
Comparison of mechanical properties of Ag/W1-xTixB2.5 and pure silver coatings deposited by PLD/HIPIMS method
Katarzyna Zielińska, Mateusz Włoczewski, Rafał Psiuk et al. (+4 more)
Transition metal borides are attracting increasing interest due to their unique properties. They are not only characterised by very high hardness, but also considerable chemical and thermal stability. Silver, on the other hand, is a good material for increasing electrical and thermal conductivity, wear resistance and has antibacterial properties due to its biological characteristics. Combining these two materials can provide superhard bilayers with increased functional properties. In this study, it was decided to synthesise Ag/WB2.5, Ag/W0.76Ti0.24B2.5 coatings and compare their properties to the individual components. The silver coating was produced by pulsed
laser deposition (PLD), while the WB2.5 and W0.76Ti0.24B2.5 coatings were formed by high-power pulsed magnetron sputtering (HiPIMS). To determine the mechanical properties, nanoindentation tests, adhesion of the coatings by scratch -test and wear resistance by abrasion in reciprocating motion were tested. In all cases, the silver film contributed to an increase in the wear resistance of the materials without major changes in the hardness results of the materials. In addition, the Ag/W0.76Ti0.24B2.5 film showed very good adhesion to the substrate. Human hand wiping simulator was also carried out using - Tribotouch. After 36 000 cycles Ag/W0.76Ti0.24B2.5 coating was slightly deformed, which was not visible macroscopically. This result is more than three times greater than for the pure silver film. It was also decided to carry out corrosion tests in an environment of 0.9% NaCl. The Ag/W0.76Ti0.24B2.5 bilayer has very good corrosion resistance, similar to pure silver.
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All authors Katarzyna Zielińska, Mateusz Włoczewski, Rafał Psiuk, Jacek Hoffman, Ewa Wojtiuk, Piotr Bazarnik, Tomasz Mościcki
Materials Science
Thermal transport in crystals: from the quantum Dyson equation to mesoscopic phonon hydrodynamics
Enrico Di Lucente, Michele Simoncelli and Nicola Marzari
Thermal transport in dielectric, non-
magnetic crystals is mediated by quantized
lattice vibrations, which drift and interact when driven out of
equilibrium by a temperature gradient. This phenomenon can be described at multiple theoretical levels, ranging from fully
quantum descriptions to semiclassical and mesoscopic continuum approaches. This review rigorously discusses the theoretical steps and approximations connecting these levels, bridging
quantum phonon Dyson and Kadanoff-Baym equations and semiclassical Boltzmann transport formalism, and discussing the coarse-graining procedures that yield mesoscopic viscous heat equations for non-diffusive, hydrodynamic heat transport in devices. We show how the Guyer-Krumhansl and dual-phase-lag equations emerge as special linear-isotropic-band and inviscid limits of the viscous heat equations, respectively; most importantly, we demonstrate that these equations predict not only Poiseuille flow and second sound, but also more exotic effects such as negative thermal resistance, steady-state thermal backflow and
vortices. We highlight how combining these frameworks with first-principles simulations connects microscopic
phonon physics to observable non-diffusive heat-transport phenomena and guides their detection, amplification, and control. We recast the viscous heat equations in terms of Helmholtz and biharmonic equations solved analytically, and use this to discuss similarities and differences between the macroscopic behavior of the
phonon fluid and other hydrodynamic systems, such as classical and electron fluids, focusing on compressibility, vorticity, and their influence on
phonon hydrodynamics. We conclude with a roadmap to generalize the tools used to describe
phonon hydrodynamics to other quasiparticles, motivating future advances in collective
quantum transport phenomena in solids.
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Materials Science · Cross-listed from physics.app-ph
Origin of effective non-Fourier heat conduction phenomena in heterogeneous materials
Róbert Kovács
Phenomenological models of non-
Fourier heat conduction often lack a strict microstructural foundation, leading to ambiguities when modeling complex heterogeneous materials. In this study, we derive a continuum heat equation beyond
Fourier's law using spatial volume averaging for a two-component system. We analytically prove that the experimentally observed static and dynamic thermal diffusivity arise directly from the distinct material properties, concluding that heterogeneous media are inherently over-diffusive. The resulting heat equation is thermodynamically compatible, and the microstructural origin allows the calculation of non-
Fourier transport coefficients. Furthermore, we demonstrate that finite-sample boundaries introduce higher-order spatial non-localities, thereby explaining the size dependence of over-
diffusion. We validate the model against experimental data across metal and carbon foams, rocks, and metal-organic frameworks.
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Materials Science · Cross-listed from cond-mat.str-el
Magnetism in antiperovskite (Li$_2$M)ChO (M = Fe, Mn, Co; Ch = S, Se) diluted magnets with fixed 1/3 filling: the key role of magnetic anisotropy
Jieyuan Zheng, Frederik L. Carstens, Lennart Singer et al. (+7 more)
We report the
magnetic properties of a series of lithium-rich antiperovskites (Li$_2M$)$Ch$O ($M$ = Fe, Co, Mn and $Ch$ = Se, S) where transition metal and lithium ions are randomly distributed on the X-sites of the X$_3$BA structure, thereby forming a strongly diluted
magnetic sublattice. Our study hence enables us to investigate the
evolution of
magnetic order at fixed 1/3-filling – which is in the vicinity but slightly above the percolation threshold – upon variation of the
spin size, the
magnetic anisotropy, and the orbital configuration. The data imply the absence of a distinct Curie-Weiss behavior up to 350~K but show rather large and weakly temperature-dependent
magnetic susceptibility. We observe clear signatures of long-range antiferromagnetic order evolving in the 1/3-filled and strongly diluted
magnetic X-site
lattice with increasing Néel temperatures from $T_{\rm{N}}\simeq 30$~K in (Li$_2$Mn)$Ch$O to $\simeq 50$~K in (Li$_2$Fe)$Ch$O and $70-90$~K in (Li$_2$Co)$Ch$O. Except for $M$ = Co, the chalcogenide has no sizable effect on $T_{\rm N}$. We conclude significant
magnetic coupling and short-range
magnetic correlations at well above $T_{\rm N}$ which is in line with the observation of a broad electron
spin resonance signal at room temperature. The actual ordering temperatures are strongly diminished by
magnetic dilution. While structural parameters such as the tolerance factor and bonding angles do not strongly affect $T_{\rm N}$, a key parameter is the
magnetic anisotropy of the transition metals.
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All authors Jieyuan Zheng, Frederik L. Carstens, Lennart Singer, Mohammed A.A. Mohamed, Luca Bischof, Alexey Alfonsov, Jan Arneth, Silke Hampel, Nico Gräßler, Rüdiger Klingeler
Materials Science
Giant exciton effects and magneto-excitonic coupling in V4S9X4 2D magnetic semiconductors
Yingjie Wei, Fan Zhang, Ying Zhao et al. (+4 more)
Room-temperature
spin-optoelectronic devices require a combination of robust ferromagnetism and giant
exciton binding, a pairing mutually exclusive in conventional
semiconductors due to
magnetic localization that screens
excitons. Cluster-assembled V4S9X4 (X = F, Cl, Br and I) monolayers overcome this bottleneck via a hierarchical design, that is, intra-cluster localized states host both local
magnetic moments and strong electron-hole interactions, while inter-cluster coupling mediates long-range ferromagnetism. Remarkably, these two-dimensional
semiconductors exhibit intrinsic ferromagnetism with Curie temperature up to 507.6 K. As a prototype, V4S9Br4 monolayer possesses a giant
exciton binding energy of 1.85 eV. Its lowest
exciton is a dark state (DI) with a radiative lifetime of 1.20 ns, whereas the first bright
exciton (BI) exhibits an ultrafast radiative decay of 86.87 ps. This stark lifetime contrast enables simultaneous ultrafast optical response and long-lived
spin information storage. Most notably, switching between ferromagnetic and antiferromagnetic order allows for wide-range tuning of
exciton lifetime, with the giant binding energy remaining nearly intact. Our findings establish cluster assembly as a powerful paradigm for designing next-generation
spin-photonic and
quantum information devices operating at room temperature.
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All authors Yingjie Wei, Fan Zhang, Ying Zhao, Lixin Zhou, Yan Su, Yu Guo, Jijun Zhao
Materials Science
Engineering Chirality in Halide Perovskites
Juan Delgado-Alvarez, Javier Castillo-Seoane, Jorge Budagosky et al. (+8 more)
The ability to control chirality in halide perovskites offers new opportunities for circularly polarized photonics,
spin-selective electronics, and
quantum information technologies. Chirality in halide perovskites is commonly achieved through chiral molecular building blocks or externally imposed photonic architectures. Although both approaches can generate strong chiroptical responses, many
spin-dependent functionalities require structural
symmetry breaking embedded within the material itself. Here we show that chirality can emerge directly during
crystal growth. By combining glancing angle deposition with controlled substrate rotation, we generate highly textured PbI2 nanostructures with growth-controlled crystallographic torsion. X-ray texture analysis reveals that substrate rotation progressively rotates the
crystal orientation during growth while preserving the c-axis orientation, resulting in a twisted texture with giant and tuneable chiroptical responses, including ellipticities of 19{\deg} and absorption dissymmetry factors approaching 0.6. The chirality programmed during growth is transferred through vapour-phase conversion into multiple halide perovskite compositions, resulting in circularly polarized luminescence with glum values up to 0.23. These findings establish growth-controlled crystallographic torsion as a previously unexplored origin of chirality in halide perovskites.
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All authors Juan Delgado-Alvarez, Javier Castillo-Seoane, Jorge Budagosky, Lidia Contreras-Bernal, Maria Alcaire, Xabier Garcia-Casas, Jose Feria, Vanda Godinho, Ana Borras, Angel Barranco, Juan R. Sanchez-Valencia
Materials Science
Machine-learned interatomic potential for sputtering of tungsten-boron surfaces
Alexandre Bergero, Jesper Byggmästar and Fredric Granberg
Boronization, where boron is deposited onto tungsten surfaces, is a key technique to reduce
plasma contamination, such as oxygen in Tokamak fusion reactors. The exact interaction between the boron atoms and the tungsten surface, and the effect of the harsh environment on these surfaces are however not fully understood, partially due to the lack of accurate atomistic simulations and interatomic potentials. Here, we develop a machine-learned interatomic potential for sputtering studies of W-B structures and deposition of boron onto tungsten surfaces. The machine-learned potential is trained to density functional theory data and allows accurate large-scale molecular dynamics simulations. Our aim is to understand how boron behaves when deposited on tungsten and how tungsten and boron are sputtered under irradiation. We observe that both the surface configuration/orientation and the surface composition affect the sputtering, and that depositing boron onto tungsten surfaces produces a dense boron layer. The developed potential shows good accuracy for both surface and bulk properties and can be used for simulations of mixed W and B systems.
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Materials Science
From Molecular Design to Optical Anisotropy: Orientation Control in BODIPY Langmuir-Blodgett Films
Lilia Huynh, Jason Bessonnet, Lucas Frédéric et al. (+7 more)
Molecular orientation within ultrathin films is a critical factor in controlling their optical and electronic properties for surface-based photonics and optoelectronics. In this study, we examine two amphiphilic boron-dipyrromethene (BODIPY) derivatives, distinguished by the number of hydrophobic alkyl chains, and investigate their organization and optical response using Langmuir–Blodgett deposition. The spatial and orientational distribution of molecules at the nanoscale is determined by combining hyperspectral imaging, photoluminescence radiation pattern analysis, and incidence-angle-resolved absorption spectroscopy. We evidence, both experimentally and based on a new and original theoretical model, the formation of organized monolayers exhibiting either in-plane or perpendicular transition dipole
alignment, depending on the molecular
symmetry. These results underscore the deep impact of molecular engineering on supramolecular order and anisotropic optical properties at interfaces, providing a robust strategy for the design of functional thin films down to the monolayer level for advanced optical devices.
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All authors Lilia Huynh, Jason Bessonnet, Lucas Frédéric, Céline Fiorini-Debuisschert, Simon Vassant, Hélène Fensterbank, Emmanuel Allard, David Kreher, Fabrice Charra, Nicolas Fabre
Materials Science
Dissipationless Photovoltaic Spin Hall Effect from Spin-current Vorticity
Longjun Xiang and Jian Wang
Spin-current vorticity (SCV) can generate the linear
magnetic spin Hall effect [\href{https://doi.org/10.1038/s41586-018-0853-0}{Nature 565, 627 (2019)}], yet its role in nonlinear
spin Hall transport has been much less explored. Here, we show that, under a dc electric field, SCV can deflect optically excited electrons to drive a dissipationless photovoltaic
spin Hall effect (PSHE), in which optical excitation by circularly and linearly polarized light is governed by the Berry
curvature and
quantum metric, respectively. Because the Berry
curvature is $\mathcal{T}$-odd whereas the
quantum metric is $\mathcal{T}$-even, their respective combinations with the $\mathcal{T}$-odd SCV give rise to $\mathcal{T}$-even and $\mathcal{T}$-odd PSHEs, where $\mathcal{T}$ denotes time-reversal
symmetry. Remarkably, we find that the
spin current of the $\mathcal{T}$-even PSHE can be reversed by switching the light helicity, as illustrated in monolayer WTe$_2$. By contrast, the $\mathcal{T}$-odd PSHE in altermagnets changes sign upon Néel-vector reversal, as demonstrated in a $d$-wave altermagnetic model. Beyond the PSHE, we show that the SCV dipole governs both the Drude and intrinsic nonlinear
spin Hall effects proposed recently. Our results reveal two switchable
spin Hall mechanisms and establish SCV as a unifying concept for understanding dissipationless nonlinear
spin Hall transport.
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Materials Science
Elastic properties of cubic silicon carbide with Si vacancies
Carlos P. Herrero, Eduardo R. Hernandez and Gabriela Herrero-Saboya
We investigate how silicon vacancies modify the elastic response and mechanical stability of cubic 3C-SiC. Our approach employs path-integral molecular dynamics simulations, including the classical-
nuclei limit, based on an efficient tight-binding
Hamiltonian, whose accuracy is validated against density-functional-theory calculations. This framework enables a quantitative assessment of nuclear
quantum effects arising from zero-point motion. Across a broad range of temperatures and hydrostatic pressures, spanning both tensile and compressive regimes, silicon vacancies are found to substantially renormalize the elastic constants $C_{11}$, $C_{12}$, and $C_{44}$, as well as the bulk modulus, relative to the defect-free
crystal. Inclusion of nuclear
quantum motion produces an additional softening of these elastic properties, particularly at low temperatures, demonstrating that
quantum fluctuations make a measurable contribution to the mechanical response of defective SiC. Vacancies also affect the mechanical stability domain of 3C-SiC, lowering the maximum sustainable tensile pressure by approximately 4 GPa for a defect concentration of 0.016 per
lattice site. These results reveal an interplay between point defects and
quantum lattice fluctuations in determining the elastic behavior of SiC, providing microscopic insight relevant for both extreme-environment structural applications and defect-based
quantum technologies.
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Materials Science
Magnetic reconstruction of the altermagnet {\alpha}-MnTe(0001) surface driven by ligand holes
Tomonori Tanaka and Yoshihiro Gohda
We show from first principles that the altermagnet {\alpha}-MnTe reconstructs its
magnetic order at the Te-terminated (0001) surface. The ground state has a ferromagnetic outermost Mn bilayer in place of the bulk-continued stacking. The driver is the holes that the surface leaves on the Te mediating the exchange within that bilayer. The computed constant-energy contours agree with photoemission maps of the surface metal. Filling the holes restores the bulk order: the carrier density can control the strength of the surface coupling and, by reversing its sign, the surface
magnetic order itself.
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Materials Science
Unraveling Lithium Storage and Defect-Modulated Transport in 2D Copper Boride: From First Principles to Machine-Learned Molecular Dynamics
Subhasis Sarkar, Rajnendra Singh, Brahmananda Chakraborty et al. (+1 more)
In this work, we combine first-principles calculations, ab initio molecular dynamics (AIMD), and machine-learning-interatomic-potential molecular dynamics (MLIP-MD) to investigate lithium storage and transport in two-dimensional Cu$_8$B$_{14}$, including an experimentally identified line-defect configuration. Pristine Cu$_8$B$_{14}$ remains metallic upon lithiation and exhibits favourable Li adsorption, a single-surface theoretical capacity of 427~mAh~g$^{-1}$, and an average open-
circuit voltage of approximately 0.53~V. The lowest Li migration barrier on the pristine surface is 0.32~eV. The line-defected structure retains a capacity of approximately 400~mAh~g$^{-1}$ while reducing the local migration barrier to 0.21~eV. To access Li dynamics beyond the picosecond time scale of AIMD, a pretrained MACE-MP-0 model was fine-tuned against system-specific DFT energies and forces and employed in nanosecond-scale simulations from 400 to 600~K. Both pristine and line-defected lithiated monolayers remain structurally stable over this temperature range. At 400~K, the line-defected system exhibits a higher in-plane Li tracer diffusivity ($3.97\times10^{-5}$~cm$^{2}$~s$^{-1}$) than the pristine monolayer ($2.50\times10^{-5}$~cm$^{2}$~s$^{-1}$), whereas the pristine system becomes more diffusive at 500 and 600~K. Arrhenius analysis yields effective activation energies of 0.147 and 0.225~eV for the line-defected and pristine systems, respectively. These results show that the line defect modifies the Li-transport landscape and its temperature dependence rather than uniformly enhancing long-range
diffusion, while preserving competitive Li-storage capacity and structural stability.
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All authors Subhasis Sarkar, Rajnendra Singh, Brahmananda Chakraborty, Sridhar Sahu
Materials Science
Finite-Temperature Thermodynamics of Cu(100) Oxidation: Missing-Row Reconstruction, Defect States, and Order-Disorder Transition from Nested Sampling
Felix Riccius, Karsten Reuter, Hendrik H. Heenen et al. (+1 more)
Metal surfaces undergo structural, compositional, and morphological changes in response to their chemical environment. Tuning the surfaces' function and stability for a given application correspondingly necessitates an understanding of how this surface
evolution couples to external conditions. Here, we demonstrate the feasibility of nested sampling simulations to obtain this coupling at first-principles predictive quality. By exploring the full configuration space, nested sampling estimates the partition function and gives direct access to desired thermodynamic ensemble averages at any temperature without prior knowledge. Computational feasibility is achieved through machine-learned interatomic potentials, an efficient GPU implementation of the sampling
algorithm and bespoke sampling moves. Applied to the early oxidation of Cu(100), the approach successfully predicts the experimentally observed, complex $(2\sqrt{2}\times\sqrt{2})$R45$^\circ$-O missing-row reconstruction. The full access to the partition function enables a detailed characterization of the temperature-dependent surface
evolution, mapping the emergence of defect states and the order-disorder transition of the reconstructed surface.
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All authors Felix Riccius, Karsten Reuter, Hendrik H. Heenen, Jutta Rogal
Materials Science
A Unified Description of Electron-Phonon Coupling and Ion Migration in Metal Halide Perovskites
Bo Cai, Yan Yang, Yoshiki Sugai et al. (+11 more)
The remarkable optoelectronic properties of metal halide perovskites are closely linked to their unusually soft and polar chemical bonds that enable both strong electron-
phonon interactions and ion migration. Yet these two defining characteristics have largely been treated as independent consequences of the same underlying chemical bonding. Here we show that they originate from a common electronic-structure framework by developing a general description linking
lattice dynamics, electron-
phonon coupling, and halide ion migration across representative Pb-based, Sn-based, and double perovskites. Spectrally resolved
phonon-mode contributions demonstrate that the low-frequency shearing modes dominate halide migration, whereas high-frequency stretching modes govern carrier scattering through the Fröhlich interaction in all three compositions. We introduce an orbital hybridization descriptor to unify these findings, which connects metal-halide bonding characteristics with the migration barrier energies and Fröhlich coupling strengths, indicating a cooperative
evolution of these two properties. These findings provide a generalized microscopic mechanism for simultaneously optimizing charge and ionic transport in soft
semiconductors.
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All authors Bo Cai, Yan Yang, Yoshiki Sugai, Maddison Wiles, Dongxu He, Yang Yang, Junmin Xia, Shufen Chen, Carla Verdi, Siyu Chen, Nan Zhang, Ming-Gang Ju, Chao Liang, Julian A. Steele
Materials Science · Cross-listed from cond-mat.mes-hall
Quantum Divergence and Topological Edge Diagnostics via Levitov Full Counting Statistics
Maolin Bo, Xiang Chen, Siyu Liu et al. (+4 more)
We propose a differential full counting statistics protocol for mesoscopic transport. Additionally, we compare terminal Fano factors and noise cumulants between gate configurations at matched k1, instead of inferring a bulk divergence sensor from a single absolute F. it is illustrated analytically for a two channel factorization via a zero temperature geometry scan. Secondary
benchmarks show that a two dimensional
lattice non
equilibrium Greens function calculation yields sub Poissonian Fano factors, whereas Kumars low temperature
quantum point contact calibration validates the numerical implementation.
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All authors Maolin Bo, Xiang Chen, Siyu Liu, Han Lu, Yunhu Zhu, Zhongkai Huang, Chuang Yao