Materials Science
Leveraging mechanical resonances for the selection of promising materials in complex phase spaces
Christopher A. Mizzi, Osman El-Atwani, Tannor T.J. Munroe et al. (+2 more)
The "high-
entropy" paradigm has been applied to a central challenge in materials science, the design of new functional materials with enhanced performance for targeted applications, with some notable successes over the last twenty years. However, the immensity of the high-
entropy design space remains a major impediment to discovering optimal compositions with tailored microstructures. Suites of high-throughput computational tools have been developed to address this problem, but there is a compelling need to inform these models with fast, economical, non-destructive, and versatile experimental guidance. In this work, we demonstrate mechanical resonance measurements can fulfill this need. Mechanical resonance measurements enable the rapid, non-destructive assessment of materials created by novel syntheses and/or processes and provide high-accuracy determinations of elastic constants to directly
benchmark models. We exemplify these capabilities on W-Ta-Cr-V-Hf and Mo-Nb-Ti-V-Zr refractory high-
entropy alloys and suggest methodologies for the wider adoption and application of mechanical resonance measurements.
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All authors Christopher A. Mizzi, Osman El-Atwani, Tannor T.J. Munroe, Saryu Fensin, Boris Maiorov
Materials Science
Precise Determination of the Long-Time Asymptotics of the Diffusion Spreadability of Two-Phase Media
Shaobing Yuan and Salvatore Torquato
The time-dependent
diffusion spreadability $\mathcal{S}(t)$ is a powerful dynamical probe of the microstructure of two-phase heterogeneous media across length scales [Torquato, S., Phys. Rev. E., 104 054102 (2021)]. It has been shown that when the spectral density takes the power-law form $\tilde{\chi}_{_V}(\mathbf{k})\sim |\mathbf{k}|^\alpha$ as the wavenumber $|\mathbf{k}|$ tends to zero, the normalized excess spreadability $\mathscr{s}^{ex}(t)$ [proportional to $\mathcal{S}(\infty)-\mathcal{S}(t)$] scales as $\mathscr{s}^{ex}(t)\sim t^{-\frac{d+\alpha}{2}}$ in the long-time limit $t\to\infty$, enabling one to determine the infinite-wavelength scaling exponent $\alpha$. An
algorithm that allows one to reliably extract the exponent $\alpha$ from long-time spreadability data was previously devised [Wang, H., Torquato, S., Phys. Rev. Appl., 17 034022 (2022)]. In this paper, we further improve this procedure to obtain $\alpha$ even more accurately by incorporating higher-order correction terms to the long-time asymptotics and by utilizing analyticity properties of $\tilde{\chi}_{_V}(k)$ at the origin. We illustrate our procedure by analyzing hyperuniform ($\alpha> 0$), typical nonhyperuniform ($\alpha=0$), and antihyperuniform ($-d < \alpha <0$) models of two-phase media. In addition, by combining the large-$t$ asymptotic expansion of $\mathscr{s}^{ex}(t)$ with the small-$t$ expansion, we have devised a two-point Padé approximant to approximate $\mathscr{s}^{ex}(t)$ for all $t$ with just a few parameters. Our findings facilitate the characterization of the microstructure of two-phase media across length scales as obtained from numerical spreadability data or experimental data obtained from NMR relaxation measurements. Our work can also be applied in the inverse design of two-phase microstructures with targeted spreadability behaviors.
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Materials Science
Inelastic Constitutive Kolmogorov-Arnold Networks: A generalized framework for automated discovery of interpretable inelastic material models
Chenyi Ji, Kian P. Abdolazizi, Hagen Holthusen et al. (+2 more)
A key problem of solid mechanics is the identification of the constitutive law of a material, that is, the relation between strain history and stress. Machine learning has lead to considerable advances in this field lately. Here we introduce inelastic Constitutive Kolmogorov-Arnold Networks (iCKANs). This novel artificial neural network architecture can discover in an automated manner symbolic constitutive laws describing both the elastic and inelastic behavior of materials. That is, it can translate data from material testing into corresponding elastic and inelastic potential functions in closed mathematical form. We demonstrate the advantages of iCKANs using both synthetic data and experimental data of the viscoelastic
polymer materials VHB 4910 and VHB 4905. The results demonstrate that iCKANs accurately capture complex viscoelastic behavior while preserving physical interpretability. It is a particular strength of iCKANs that they can process not only mechanical data but also arbitrary additional information available about a material (e.g., about temperature-dependent behavior). This makes iCKANs a powerful tool to discover in the future also how specific processing or service conditions affect the properties of materials.
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All authors Chenyi Ji, Kian P. Abdolazizi, Hagen Holthusen, Christian J. Cyron, Kevin Linka
Materials Science
Fracture Properties of Green Nano Fibrous Network with Random and Aligned Fibre Distribution: A Hierarchical Molecular Dynamics and Peridynamics Approach
Razie Izadi, Raj Das, Nicholas Fantuzzi et al. (+1 more)
Polylactic acid (PLA) nanofibrous networks have gained substantial interest across various engineering and scientific disciplines, such as tissue engineering, drug delivery, and filtration, due to their unique and multifunctional attributes, including biodegradability, tunable mechanical properties, and surface functionality. However, predicting their mechanical behaviour remains challenging due to their structural complexity, multiscale features, and variability in material properties. This study presents a hierarchical approach to investigate fracture phenomena in both aligned and randomly oriented nanofibrous networks by integrating atomistic modelling and nonlocal continuum mechanics, namely peridynamics. At the nanoscale, all-atom molecular dynamics simulations are employed to apply tensile loads to freestanding pristine and silver-doped PLA nanofibres, where key mechanical properties such as Young's modulus, Poisson's ratio, and critical energy release rate are determined. A new method is introduced to transfer data from molecular dynamics to peridynamics by ensuring convergence of the tensile response of a single fiber in both frameworks. This nano-to-micro coupling technique is then used to examine the Young's modulus, fracture toughness in modes I and II, and crack propagation in PLA nanofibrous networks. The proposed framework can also incorporate the effects of surface coating and fiber arrangements on the measured properties. This research paves the way for the development of stronger and more durable eco-friendly nanofibrous networks with optimised performance.
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All authors Razie Izadi, Raj Das, Nicholas Fantuzzi, Patrizia Trovalusci
Materials Science
First-principles Newns-Anderson Hamiltonian Construction for Chemisorbed Hydrogen at Metal Surfaces
Nils Hertl, Zsuszanna Koczor-Benda and Reinhard J. Maurer
The Newns-Anderson
Hamiltonian is widely used to describe adsorption at gas-solid interfaces, yet its construction typically relies on simplifying assumptions such as constant coupling and the wideband limit approximation. Here, we present a first-principles approach to construct Newns-Anderson
Hamiltonians by applying projection operator diabatisation to
Hamiltonian matrices obtained from Kohn-Sham density functional theory calculations. We demonstrate this method for chemisorbed hydrogen on three fcc metal(111) surfaces: Al, Cu, and Pt. To validate the electronic coupling between adsorbed hydrogen and the metal surface, we compute the projected density of states, electronic tunnelling lifetimes, and vibrational lifetimes from the constructed Newns-Anderson
Hamiltonians and find good agreement with reference calculations. Analysis of the chemisorption function reveals that the wideband limit approximation is valid for H/Al(111) but has limited applicability for H/Cu(111) and H/Pt(111).
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Materials Science
Discovery of Polymer Electrolytes with Bayesian Optimization and High-Throughput Molecular Dynamics simulations
Antonia S. Kuhn, Jurğis Ruža, KyuJung Jun et al. (+2 more)
Polymer electrolytes are critical for safe, high-energy-density solid-state batteries, yet discovering candidates that balance high ionic conductivity with high transference numbers remains a significant challenge. In this work, we develop a high-throughput screening platform that utilizes molecular dynamics simulations to navigate a chemical space of 1.7 million hypothetical
polymer electrolyte candidates. Data from previous literature is used to warm-start batch
Bayesian optimization for iteratively selecting new
polymer electrolytes to evaluate. We iteratively identified, evaluated and analyzed 767 homopolymers as potential candidates. Our results reveal several candidates with transport properties exceeding the
benchmark polyethylene
oxide (PEO)/LiTFSI system. Crucially, our optimization campaigns for ionic conductivity and Li-diffusivity demonstrate that branched architectures and ketone functional groups significantly enhance ion-hopping mechanisms within the
polymer matrix. We provide an in-depth mechanistic comparison of Li vs. Na cation transport and offer our open-source framework to accelerate the discovery of
liquid, gel, and multi-cation electrolyte systems.
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All authors Antonia S. Kuhn, Jurğis Ruža, KyuJung Jun, Pablo Leon, Rafael Gómez-Bombarelli
Materials Science
The influence of Y content on grain structure evolution in Mg-Y alloys
Qianying Shi, Vaidehi Menon, Liang Qi et al. (+1 more)
To advance the understanding of microstructural
evolution behavior in Mg-rare earth
alloys, the effect of yttrium (Y) addition on static recrystallization and grain growth in Mg
alloys was systematically investigated in extruded Mg-1wt.%Y and Mg-7wt.%Y
alloys. Y addition was found to significantly retard the microstructural
evolution, primarily due to its solute drag effect arising from Y segregation at grain boundaries. The relative intensity of solute drag effects from different alloying elements in Mg
alloys was further assessed from both thermodynamic and kinetic perspectives, considering their grain boundary segregation tendencies and diffusivities. Additionally, static recrystallization in Mg-Y
alloys was observed to proceed via a two-stage behavior characterized with two distinct JMAK exponents, indicating the heterogeneous nucleation of recrystallized grains. Abnormal grain growth (AGG) behavior was observed in these Mg-Y
alloys. Overall, this study highlights the critical role of Y segregation at grain boundaries in controlling recrystallization and grain growth kinetics in Mg-Y
alloys. This provides new insights into the design of thermally stable Mg
alloys with refined microstructures.
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All authors Qianying Shi, Vaidehi Menon, Liang Qi, John Allison
Materials Science
Interpretable Machine Learning of Nanoparticle Stability through Topological Layer Embeddings
Felipe Hawthorne, Leandro Seixas, James M. Almeida et al. (+2 more)
The stability of chemically complex nanoparticles is governed by an immense configurational space arising from heterogeneous local atomic environments across surface and interior regions. Efficiently identifying low-energy configurations within this space remains a central challenge for first-principles-based materials discovery, particularly when the available reference data are limited. Here, we introduce a data-efficient and physically interpretable machine-learning framework based on a fragmented, layer-resolved descriptor that explicitly decomposes nanoparticles into surface, intermediate, and core environments using a
topology-driven definition. This representation preserves a compact and fixed feature dimensionality while retaining spatial resolution, enabling controlled emphasis on different regions of the nanoparticle through physically motivated weighting schemes. Coupled with gradient-boosted decision tree models and a ranking-based learning strategy, the proposed framework enables accurate identification of the most stable nanoparticle configurations using only a few hundred density functional theory reference calculations. Ranking performance metrics demonstrate near-saturation of correlation, high top-k recall, and rapidly vanishing regret at moderate training-set sizes, highlighting the strong data efficiency of the approach. Beyond predictive performance, layer-weighting and SHAP-based interpretability analyses reveal how surface segregation, coordination
topology, and local chemical disorder contribute differently to stability across spatial regions of the nanoparticle. These insights provide a transparent physical interpretation of the learned models and establish a natural pathway toward active learning-driven exploration of complex nanoparticle configurational spaces.
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All authors Felipe Hawthorne, Leandro Seixas, James M. Almeida, Cristiano F. Woellner, Raphael M. Tromer
Materials Science · Cross-listed from cond-mat.mes-hall
Prediction of two-dimensional $\pi$-electron half-metallic ferrimagnets
J. Phillips, J. C. G. Henriques, J. Fernández-Rossier et al. (+1 more)
We propose a strategy to obtain conducting organic materials with fully
spin-polarized
Fermi surface, lying at a singular flat band, with antiferromagnetically coupled
magnetic moments that reside in pi-orbitals of nanographenes. We consider a honeycomb
crystal whose unit
cell combines two different molecules with $S=1/2$: an Aza-3-Triangulene, a molecule with orbital degeneracy, and a 2-Triangulene. The analyzed system is half-metallic with a ferrimagnetic order, presenting a zero net total
magnetic moment per unit
cell. We combine density functional theory calculations with a Hubbard model
Hamiltonian to compute the
magnetic interactions, the bands, the intrinsic Anomalous
Hall effect, and the collective
spin excitations. We obtain very large intermolecular exchange couplings, in the range of 59 meV. Based on the
spin excitation dispersion, we estimate thermal stability in the range of 100 Kelvin. When the magnetization is off-plane, intrinsic
spin orbit coupling in
graphene opens up a topological gap that, despite being very small, leads to a quantized
Hall conductance in the tens of mK range, but is thermally smeared above 1 Kelvin.
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All authors J. Phillips, J. C. G. Henriques, J. Fernández-Rossier, A. T. Costa
Materials Science
Multi-Method Li Plating Characterization of a Commercial 26 Ah Li-Ion Pouch-Cell
Christiane Rahe, Heinrich Ditler, Thorsten Tegetmeyer-Kleine et al. (+21 more)
Lithium (Li) plating on graphite is a significant degradation mechanism in Li-ion batteries. While numerous experimental techniques have been used to study Li plating in laboratory
cells, investigations of commercial high-energy
cells often rely on electrochemical methods. Here we present and classify various methods for detecting Li plating on a commercial A123 pouch
cell. In a round robin study across multiple battery research laboratories, Li-plated graphitic electrode material was analyzed using electrochemical, microscopic, and spectroscopic methods capable of detecting metallic Li deposits. After
cell opening, their overall distribution on the anode surface was examined using a flatbed scanner to ensure comparability of the samples. Optical and electron microscopy provided detailed surface and, in combination with a focused ion beam, subsurface structure and morphology. Spectroscopic methods confirmed the presence and onset of plated Li with varying sensitivity. Moreover, spectroscopic and imaging techniques were combined correlatively where possible. Availability and measurement duration of each technique was compared. Optical methods are fast and easy to use; thus, they are recommended for most samples, with spectroscopic confirmation reserved for reference samples. This
multimodal study demonstrates a range of methods that can be used alone or in combination to qualitatively or quantitatively detect Li-plating.
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All authors Christiane Rahe, Heinrich Ditler, Thorsten Tegetmeyer-Kleine, Marius Flügel, Thomas Waldmann, Margret Wohlfahrt Mehrens, Philipp Schleker, Peter Jakes, Beatrice Wolff, Josef Granwehr, Rüdiger-A. Eichel, Jiří Vacík, Giovanni Ceccio, Antonino Cannavo, Ivana Pivarníková, Ralph Gilles, Peter Müller-Buschbaum, Adrian Mikitisin, Joachim Mayer, Michael Noyong, Ulrich Simon, Marius Bolsinger, Volker Knoblauch, Dirk Uwe Sauer
Materials Science · Cross-listed from cond-mat.mes-hall
Charge and energy transport in graphene with smooth finite-range disorder
Juan A. Cañas, Daniel A. Bonilla, J. C. Pérez-Pedraza et al. (+1 more)
We investigate charge and energy transport in monolayer
graphene with smooth finite-range disorder, modeled by soft
impurity potentials. Using a continuum Dirac model, we go beyond the Born approximation by computing the exact scattering
matrix for individual
impurities. This captures the full nonperturbative physics of smooth disorder. From the exact scattering data, we evaluate transport coefficients by solving the Boltzmann equation with energy-resolved phase shifts. We analyze electrical and electronic thermal conductivities versus carrier density and temperature, including deviations from the Wiedemann-Franz law. Our results reveal that finite-range disorder nontrivially modifies charge and heat currents, especially at low energies where perturbative methods fail. These findings provide a more accurate transport characterization for disordered Dirac materials and clarify how smooth disorder governs energy flow in
graphene.
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All authors Juan A. Cañas, Daniel A. Bonilla, J. C. Pérez-Pedraza, A. Martín-Ruiz
Materials Science
Atomic-Scale Surface Imaging of bulk Epitaxial CsPbBr3 Perovskite Single Crystals on Mica using Light Assisted Scanning Tunneling Microscopy at Low-Temperature (80 K)
Eric Duverger, Vladimir Bruevich, Vitaly Podzorov et al. (+1 more)
Epitaxial single-crystalline CsPbBr3 perovskite films on mica, prepared ex-situ, are explored using a low-temperature scanning tunneling microscope (STM) by probing the unoccupied electronic states of their surface in ultra-high
vacuum (UHV) at 80 K. Light-assisted STM measurements under a broadband illumination with visible light were employed to enhance and stabilize surface conductivity. STM imaging across the surface of macroscopic bulk CsPbBr3 films reveals large flat terraces characterized by a specific type of surface reconstruction, consisting of parallel rows of U-shaped atomic nanostructures. These structures are spaced by 12 angstroms and exhibit an internal periodicity of 5.1 angstroms. Density functional theory (DFT) calculations reproduce the experimental observations and reveal a competition between different orthorhombic CsPbBr3(110) surface reconstructions: a Cs-rich structure, identified as the most energetically stable, and three alternative PbBr rich reconstructions, which are slightly higher in energy yet remain consistent with the STM data. Additional analyses that explicitly account for the mica substrate exclude the cubic CsPbBr3 phase and other orthorhombic surface orientations, while showing that variations in the mica surface termination do not alter the preferred CsPbBr3(110) reconstruction. This combined approach thereby confirms our assignment and resolves previous STM interpretations of CsPbBr3.
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All authors Eric Duverger, Vladimir Bruevich, Vitaly Podzorov, Damien Riedel
Materials Science
Chiral phonons in sixfold chiral CrSi$_2$: Raman spectroscopy and first-principles calculations
Gakuto Kusuno, Shingo Kisanuki, Yusuke Kousaka et al. (+2 more)
Chiral phonons have been identified in several
chiral crystals, primarily in those with trigonal
symmetry and threefold screw axes. In this study,
chiral phonons in CrSi$_2$, a
chiral crystal with a sixfold helical structure, were investigated. Circularly polarized Raman spectroscopy revealed a subtle splitting of doubly degenerate $E_2$
phonon modes between cross-circular polarization configurations. These observations, supported by first-principles
phonon calculations, indicate the presence of
chiral phonons in CrSi$_2$, expanding the scope of materials that exhibit
chiral vibrational modes beyond the conventional trigonal class.
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All authors Gakuto Kusuno, Shingo Kisanuki, Yusuke Kousaka, Yoshihiko Togawa, Takuya Satoh
Materials Science · Cross-listed from physics.app-ph
g4chargeit: Geant4-based kinetic Monte Carlo simulations of charging in dielectric materials
Kush P. Gandhi, Advik D. Vira, William M. Farrell et al. (+5 more)
We present g4chargeit, a kinetic Monte Carlo framework built on Geant4 for self-consistent simulation of time-dependent electrostatic charging in dielectric materials. The model explicitly incorporates
stochastic particle transport and scattering processes using validated Geant4 cross-sections, while self-consistently evolving the electric potential and field. As a representative application, we simulate the charging of regolith grains under average dayside conditions on the Moon. The surface of the Moon, in addition to other airless planetary bodies, are regularly exposed to
solar ultraviolet
photons and
solar-wind
plasma, creating a radiation environment in which electrostatic interactions among regolith grains become significant. Until now, simulations of regolith charging have often relied on analytical approximations that oversimplify grain geometry and interaction mechanisms. Our Geant4-based simulations reveal charge accumulation within intergrain micro-cavities, leading to repulsive electrostatic forces consistent with experimental observations. The framework establishes a multiscale approach that links microscopic scattering events to the continuity equation of surface charge density and to the formation of macroscopic surface charge patches in complex grain geometries. Although demonstrated here for planetary regolith, the method is general and applicable to a broad range of dielectric charging problems. The code is openly available at https://github.com/kgandhi63/g4chargeit.git.
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All authors Kush P. Gandhi, Advik D. Vira, William M. Farrell, Nikolai Simonov, Alvaro Romero-Calvo, Thomas M. Orlando, Phillip N. First, Zhigang Jiang
Materials Science
Unveiling Photoluminescence Signatures of Magneto-Optical Coupling in Layered Hybrid Manganese Chloride Perovskites
Yaiza Asensio, Samuele Mattioni, Daniel Vaquero et al. (+9 more)
Understanding the interplay between
magnetic ordering and light emission is crucial for developing magneto-optical technologies. However, this phenomenon is poorly understood since observations of this coupling vary significantly across materials. In this context, hybrid organic-inorganic metal halide perovskites (HOIPs) that incorporate Mn2+ ions are a chemically and structurally tunable platform for exploring this phenomenon, since they exhibit
magnetic ordering and photoluminescence (PL) emission. Here, we study two
antiferromagnetic Mn-based HOIPs with different organic cations that result in distinct
lattice stiffness, Mn2+-Mn2+ distance and octahedral distortion. Temperature-dependent PL excitation spectroscopy reveals changes in
crystal field splitting energy and Racah parameters well above the Néel temperature (TN), indicating the emergence of Mn2+-Mn2+
magnetic interactions prior to reach long-range
magnetic ordering. These variations align with the observed changes in temperature-PL
evolution. The compound with a more rigid
lattice shows stronger changes closer to TN, suggesting combined effects of
magnetic polarons and
spin-canting. In contrast,
magnetic polaron-induced
magnetic modifications prevail in the HOIP with a softer
lattice. These results reveal the complexity of the magneto-optical coupling in Mn-based HOIPs and provide new insights into this field extensible to other 2D materials that exhibit this phenomenon with potential for advanced magneto-optical applications.
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All authors Yaiza Asensio, Samuele Mattioni, Daniel Vaquero, Cédric A. Cordero-Silis, Houman Bahmani Jalali, Dorwal Marchelli, Marco Gobbi, Fèlix Casanova, Francesco Di Stasio, Marcos H.D. Guimarães, Luis E. Hueso, Beatriz Martín-García
Materials Science
Effect of oxygen content on optical, structural, and dielectric properties of Al$_x$Ta$_y$O$_z$$ thin films
Pavel Ondračka, Richard Drevet, Daniel Franta et al. (+3 more)
This study reports on the optical, structural, and dielectric properties of aluminum tantalum
oxide (Al$_x$Ta$_y$O$_z$) thin films deposited at low temperature on silicon and steel substrates by pulsed direct current reactive magnetron sputtering of a target containing 80 at.% aluminum and 20 at.% tantalum in Ar/O$_2$ atmosphere. Oxygen flow rates ranging from 5.0 to 20 sccm corresponded to O content changes from 57.7 to 69.6 at.% and resulted in large differences in dielectric behavior, from films with no measurable dielectric strength to a dielectric strength of 231 V$\mu$m$^{-1}$, respectively. Ab initio calculations were employed to explain the large property changes, and we show that a decrease in the dielectric strength can be linked to the formation of metal-metal bonds in the material, when the O content is less than what would correspond to a stoichiometric Ta$_2$O$_5$ and Al$_2$O$_3$ mixture. The electronic states corresponding to the metal–metal bonds are located in the band gap close to the top of the valence band, leading to an effective band gap reduction, which is directly supported by X-ray photoelectron spectroscopy valence band measurements and by a broad optical absorption in the visible region.
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All authors Pavel Ondračka, Richard Drevet, Daniel Franta, Jan Dvořák, Ivan Ohlídal, Petr Vašina
Materials Science
Low-Field Ferroelectric Switching realised by Forced Harmonic Oscillation of Domain Walls
Niyorjyoti Sharma, Nathan Black, Joseph G. M. Guy et al. (+6 more)
Conventionally, dc fields are used for switching dipole orientations in ferroelectrics. Such fields tilt the potential surface experienced by domain walls and thereby lower activation energies for their movement: escape from tilted potential wells is then realised by thermal excitation, allowing a "creep" process of pinning and depinning to develop. Borrowing ideas of domain wall resonance from the
magnetic racetrack community, we show that ac fields, applied at the right frequency, can cause switching at much lower field magnitudes than dc ones (by factors of 4-5). Ferroelectric wall motion appears to be overdamped in the system studied (relaxor strontium barium niobate) and so the maximum in switching efficacy observed, at ~100 kHz, cannot be associated with resonant amplification, which needs an underdamped environment. Instead, in this high viscosity system, the frequency at which the maximum switching efficacy occurs seems to represent a compromise between the attempt frequency for wall depinning (which increases with frequency) and the extent to which energy is transferred to the wall within each field cycle (which decreases with frequency). Notwithstanding the absence of true resonance, the observation that ac excitation can dramatically reduce the bias levels needed for ferroelectric switching could still have significant ramifications for low energy
memory technology.
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All authors Niyorjyoti Sharma, Nathan Black, Joseph G. M. Guy, Eftihia Barnes, Kristina M. Holsgrove, Brian J. Rodriguez, Raymond G.P. McQuaid, J. Marty Gregg, Amit Kumar
Materials Science · Cross-listed from quant-ph
Near-single-domain superconducting aluminum films on GaAs(111)A with exceptional crystalline quality for scalable quantum circuits
Hsien-Wen Wan, Yi-Ting Cheng, Chao-Kai Cheng et al. (+6 more)
We have reproducibly grown near-single-domain superconducting aluminum (Al) films on GaAs(111)A wafers using molecular beam epitaxy. Synchrotron X-ray diffraction revealed twin-domain ratios of 0.00005 and 0.0003 for 19.4-nm- and 9.6-nm-thick films, respectively-the lowest reported for Al on any substrate and long considered unattainable for practical device platforms. Azimuthal scans across off-normal Al{$11\bar{1}$} reflections exhibit narrow full width at half maximum (FWHM) values down to $0.55^\circ$, unmatched by epi-Al grown by any other method. Normal scans showed a well-defined (111) orientation with pronounced Pendellösung fringes, and $\theta$-rocking-curve FWHM values down to $0.018^\circ$; the former indicates abrupt film-substrate and
oxide-film interfaces. Electron backscatter diffraction mapping confirms macroscopic in-plane uniformity and the absence of $\Sigma$3 twin domains. Atomic force microscopy and scanning transmission electron microscopy confirmed atomically smooth surfaces and abrupt heterointerfaces. The films exhibit critical temperatures approaching bulk values, establishing a materials platform for scalable, high-coherence superconducting
qubits.
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All authors Hsien-Wen Wan, Yi-Ting Cheng, Chao-Kai Cheng, Jui-Min Chia, Chien-Ting Wu, Sheng-Shiuan Yeh, Chia-Hung Hsu, Jueinai Kwo, Minghwei Hong
Materials Science
Photocatalytic methanol dehydrogenation promoted synergistically by atomically dispersed Pd and clustered Pd
Zhuyan Gao, Tiziano Montini, Junju Mu et al. (+4 more)
Supported metal in the form of single atoms, clusters, and particles can individually or jointly affect the activity of supported heterogeneous catalysts. While the individual contribution of supported metal to the overall activity of supported photocatalysts has been identified, the joint activity of mixed metal species is overlooked because of their different photoelectric properties. Here, atomically dispersed Pd (Pd1) and Pd clusters are loaded onto CdS, serving as oxidation and reduction sites, respectively, for methanol dehydrogenation. The Pd1 substitutes Cd2+, forming hole-trapping states for methanol oxidation and assisting the dispersion of photo-deposited Pd clusters. Therefore, methanol dehydrogenation on CdS with supported Pd1 and Pd clusters exhibits the highest turnover frequency of 1.14 s-1 based on Pd content, and affords H2 and HCHO with a similar apparent
quantum yield of 87 +/- 1% at 452 nm under optimized reaction conditions. This work highlights the synergistic catalysis of supported metal for improved photocatalytic activity.
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All authors Zhuyan Gao, Tiziano Montini, Junju Mu, Nengchao Luo, Emiliano Fonda, Paolo Fornasiero, Feng Wang
Materials Science
Wide-Surface Furnace for In Situ X-Ray Diffraction of Combinatorial Samples using a High-Throughput Approach
Giulio Cordaro, Juande Sirvent, Cristian Mocuta et al. (+7 more)
The combinatorial approach applied to functional
oxides has enabled the production of material libraries that formally contain infinite compositions. A complete ternary diagram can be obtained by pulsed
laser deposition (PLD) on 100 mm silicon wafers. However, interest in such materials libraries is only meaningful if high-throughput characterization enables the information extraction from the as-deposited library in a reasonable time. While much commercial equipment allows for XY-resolved characterization at room temperature, very few sample holders have been made available to investigate structural, chemical, and functional properties at high temperatures in controlled atmospheres. In the present work, we present a furnace that enables the study of 100 mm wafers as a function of temperature. This furnace has a dome to control the atmosphere, typically varying from nitrogen gas to pure oxygen atmosphere with external control. We present the design of such a furnace and an example of X-ray diffraction (XRD) and fluorescence (XRF) measurements performed at the DiffAbs beamline of the SOLEIL synchrotron. We apply this high-throughput approach to a combinatorial library up to 735 {\textdegree}C in nitrogen and calculate the thermal expansion coefficients (TEC) of the ternary system using custom-made MATLAB codes. The TEC analysis revealed the potential limitations of Vegard's law in predicting
lattice variations for high-
entropy materials.
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All authors Giulio Cordaro, Juande Sirvent, Cristian Mocuta, Fjorelo Buzi, Thierry Martin, Federico Baiutti, Alex Morata, Albert Tarancòn, Dominique Thiaudière, Guilhem Dezanneau
Materials Science
Dielectric Screening in Electromagnetic Dressing of Semiconductors
Quentin Courtade, Umberto Dellasette, Sotirios Fragkos et al. (+4 more)
Nonequilibrium manipulation of
quantum materials via electromagnetic dressing provides an on-demand route to tailoring electronic band structures through Floquet engineering. Time- and angle-resolved photoemission spectroscopy offers a direct means to probe these light-dressed electronic states. In such photoemission experiments, dressing can also occur for quasi-free electrons outside the material, giving rise to Volkov states. In certain cases, strong surface screening reduces the penetration of the driving field into the solid, resulting in Volkov contributions that dominate over Floquet ones. In this work, we systematically investigate the influence of materials' dielectric properties on Floquet-Volkov dressing of
semiconductors, focusing on bulk layered van der Waals materials GeS, SnS, and 2H-WSe$_2$. First, by combining a simple model based on Fresnel equations with an electron-scattering description of Volkov amplitudes, we use polarization-dependent Volkov sideband intensities to extract a lower bound for the real part of the materials' dielectric functions, which typically lie between the reported dielectric constants for monolayer and bulk
crystals. We demonstrate that increasing the fluence of the pump
laser enables the generation of high-order Volkov sidebands which exhibit clear signatures of nonlinear light-matter interactions. Finally, we show that for our experimental geometry, the quasi-transparent nature of
semiconductors in below-band-gap driving regime allows the optical pump to propagate within the sample and undergo multiple total internal reflections, producing temporally delayed Volkov replicas in pump-probe measurements via dressing of photoelectrons by evanescent fields. These systematic studies uncover previously unexplored aspects of Floquet-Volkov dressing in solids, highlighting the role of dielectric screening of the driving field.
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All authors Quentin Courtade, Umberto Dellasette, Sotirios Fragkos, Stéphane Petit, Dominique Descamps, Yann Mairesse, Samuel Beaulieu
Materials Science
Why are there so few non-altermagnetic antiferromagnets?
Nicola A. Spaldin, Sang-Wook Cheong and Sinead Griffin
We review the conditions that cause or prohibit non-relativistic
spin splitting of the energy bands in antiferromagnets. We propose that the existence of
spin splitting in magnetically ordered systems is the default scenario and outline the criteria that must be met to avoid it. We discuss some of the properties of those special antiferromagnets that succeed in preserving their
spin degeneracy.
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Materials Science
NextCrystal: a Symmetry-Driven Generative Framework for Crystal Structure Prediction
Jinming Mu, Lixin He, Xudong Zhu et al. (+1 more)
Crystal structure prediction (CSP), which aims to predict the 3D atomic arrangement of a
crystal from its composition, is central to materials discovery and mechanistic understanding.
Crystal symmetry plays a crucial role in CSP, but given the composition in a unit
cell, existing methods either struggle with the NP-hard combinatorial challenge of enforcing
symmetry rigorously or rely on retrieving known templates, inherently limiting both physical fidelity and the discovery of genuinely new materials. To address this challenge, we introduce NextCrystal, a
symmetry-driven generative framework that employs large
language models to encode chemical semantics and directly generate fine-grained Wyckoff site patterns from atomic stoichiometry, eliminating reliance on database lookups. To overcome the combinatorial complexity of site assignments, we incorporate domain knowledge via an efficient, linear-complexity heuristic beam search, rigorously enforcing algebraic consistency between site multiplicities and atomic stoichiometry. By integrating this
symmetry-consistent template into a
diffusion backbone, the framework constrains the
stochastic generative trajectory to a physically plausible
geometric manifold. NextCrystal achieves state-of-the-art performance on stability, uniqueness, and novelty (SUN)
benchmarks, as well as superior structural matching, establishing a rigorous paradigm for exploring previously unexplored crystallographic space without relying on prior structural templates. As a representative application, first-principles screening of HfO2 candidates generated by NextCrystal identifies a previously unreported dynamically stable Pnma phase, 0.056~eV/atom lower in energy than the conventional high-pressure Pnma phase.
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All authors Jinming Mu, Lixin He, Xudong Zhu, Shi Yin
Materials Science
Rotational Soft Modes and Octahedral Distortion as Design Principles for Ultralow Thermal Conductivity in Halide Materials
Yu Wu, Luman Shang, Yufan Liu et al. (+4 more)
We establish that ultralow
lattice thermal conductivity in halide perovskites and related octahedral framework materials arises from two distinct and complementary mechanisms: (i) halogen-halogen-enabled rotational soft modes that reshape the low-frequency spectrum and intensify
phonon scattering, and (ii) static octahedral distortions that further enhance anharmonicity and reduce
phonon lifetimes. Using first-principles calculations on CsPbBr3, we demonstrate that Br-Br interactions induce rotational soft modes that decongest the
phonon spectrum and enhance three- and four-
phonon scattering, strongly suppressing particle-like thermal conductivity (kappa_p). Independently, static octahedral distortions further reduce kappa_p by amplifying anharmonicity while leaving wave-like conductivity (kappa_c) intact. Based on these mechanistic insights, we introduce a
geometric distortion factor rho and perform a high-throughput screening that first selects materials with halogen-coordinated octahedral building blocks-ensuring the presence of rotational soft modes-and then identifies those with pronounced distortion. This strategy uncovers TaGaI8 with an ultralow kappa_L = 0.11 W/mK at room temperature. This work establishes halogen-halogen-enabled rotational soft modes and octahedral distortions as transferable design principles for octahedra-containing halides, spanning both extended frameworks and molecular-cluster motifs, for discovering ultralow-kappa_L materials.
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All authors Yu Wu, Luman Shang, Yufan Liu, Shuming Zeng, Liujiang Zhou, Hao Zhang, Chenhan Liu
Materials Science
Elucidating Na$_2$KSb band structure: near-band-gap photoemission spectroscopy and DFT calculations
S. A. Rozhkov, V. V. Bakin, S. V. Eremeev et al. (+7 more)
The electronic band structure of Na$_{2}$KSb was studied by a combination of low-energy photoemission spectroscopy and density functional theory (DFT) calculations. The optical and photoemission
quantum efficiency (QE) spectra, along with longitudinal energy distribution curves (EDCs) of multialkali Na$_{2}$KSb(Cs,Sb) photocathodes were measured in the temperature range of 80–295 K. The thresholds of various band-to-band transition in Na$_{2}$KSb were observed in the optical and QE spectra of Na$_{2}$KSb(Cs,Sb) photocathodes. The
evolution of EDC derivatives with varying
photon energy reveals a fine structure related to the emission of two types of electrons: (i) ballistic electrons, which are excited from heavy hole, light hole and split-off valence bands, and (ii) photoelectrons, that are captured in the side valleys of Na$_{2}$KSb conduction band. The analysis of EDCs and QE spectra allowed us to determine the band structure parameters of Na$_{2}$KSb at $T = 80$ K, including the band gap $E_{\text{g}} = 1.52 \pm 0.02$ eV,
spin-orbit splitting $\Delta_{\text{SO}} = 0.59 \pm 0.04$ eV and the energy separations between $\Gamma$ and side valleys of the conduction band: $\Delta_{\Gamma-\text{X}1} = 0.41 \pm 0.05$ eV and $\Delta_{\Gamma-\text{X}2} = 0.65 \pm 0.05$ eV. The experimentally determined band gaps and side valley positions, as well as the energies of the final electronic states of optical transitions are in good agreement with the DFT calculations. The obtained data on the hot electron dynamics and electronic band structure of Na$_{2}$KSb are crucial to improve the understanding of the photoemission processes in this material and will contribute to the development of the robust
spin-polarized electron sources with multialkali photocathodes.
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All authors S. A. Rozhkov, V. V. Bakin, S. V. Eremeev, V. S. Rusetsky, V. A. Golyashov, D. A. Kustov, D. K. Orekhov, H. E. Scheibler, V. L. Alperovich, O. E. Tereshchenko
Materials Science
Role of atomic vacancies and second-neighbor antiferromagnetic-exchange coupling in a ferromagnetic nanoparticle
Harun Al Rashid, Muskan Sharma, Shruti et al. (+1 more)
Several factors may be responsible for disorder and frustration in a
magnetic nanoparticle, including atomic vacancies on the surface and inside,
impurity atoms, long-range
magnetic exchange coupling, etc. We use Monte-Carlo simulations within the Heisenberg model to examine the role of randomly distributed atomic vacancies and long-range
magnetic-exchange coupling on the temperature-dependent
magnetic properties of
ferromagnetic nanoparticles. In particular, we study the role of the second-neighbor
antiferromagnetic exchange coupling and missing atoms inside the particle resulting in broken nearby bonds. We find that both factors may enhance the superparamagnetic behaviors of such particles.
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All authors Harun Al Rashid, Muskan Sharma, Shruti, Dheeraj Kumar Singh
Materials Science
Finite-size effects and energy alignment in molecular XANES under periodic boundary conditions: A systematic comparison of core-hole treatments
Yu Fujikata, Yasuji Muramatsu and Teruyasu Mizoguchi
X-ray absorption near-edge structure (XANES) provides element-specific insight into local electronic and structural environments, but quantitative interpretation of molecular XANES under periodic boundary conditions (PBC) remains challenging due to finite-size effects and core-hole treatments. In this work, we systematically investigate how core-hole approximations and charge compensation schemes affect transition energies, energy
alignment, and chemical-shift reproducibility in PBC-DFT-based molecular XANES calculations. Using ethane as a model system, we show that the full core-hole (FCH) approach exhibits pronounced supercell-size dependence originating from interactions between background charge and charged molecules, with transition energies largely changed by leading-order finite-size terms. In contrast, the excited core-hole (XCH) method rapidly converges owing to its neutral final state. We further demonstrate that most finite-size effects in FCH can be removed by Makov-Payne corrections based on multipole expansion of the electrostatic energy of charged supercells under PBC. Furthermore, we propose a simple
Fermi-level-based energy correction (EF/2) that provides comparable improvement using only a single supercell. Extending the analysis to an n-alkane series reveals that while intrinsic electronic-structure changes govern peak shifts for small molecules, systematic energy drifts persist in FCH for larger molecules, whereas XCH and FCH+EF/2 remain stable. Finally, for small molecules at the C and N K-edges, XCH and FCH+EF/2 accurately reproduce experimental chemical shifts, whereas uncorrected FCH fails. These results provide practical guidelines for reliable energy
alignment and chemical-shift analysis in molecular XANES under PBC, supporting robust applications to molecular, adsorption, and interfacial systems.
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