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Physics Condensed Matter Materials Science

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Friday 27 March

Materials Science · Cross-listed from cond-mat.soft

Liquid-state structural asymmetry governs species-selective crystallization in multicomponent systems

Rikuya Ishikawa, Kyohei Takae, Daisuke Takegami et al. (+2 more)

Multicomponent crystals are often assumed to form nearly random solid solutions when thermodynamically stable. However, crystal growth proceeds from structurally heterogeneous liquids, raising the possibility that the liquid state may influence which species are incorporated into the growing crystal. Here we demonstrate that liquid-state structural asymmetry can induce species-selective crystallization in multicomponent systems. Using molecular dynamics simulations of a multivalent rocksalt-type model (AgPbBiTe$_3$), we find that cations with higher valence readily form locally crystal-compatible coordination environments in the liquid and are efficiently incorporated into the growing lattice, whereas lower-valence cations exhibit more disordered liquid coordination and attach less efficiently at the crystal-liquid interface. This asymmetry leads to species-selective incorporation and slower crystal growth. Depth-resolved photoelectron spectroscopy measurements on AgPbBiTe$_3$ further reveal enhanced Ag concentration near grain-boundary and surface regions, consistent with the selective incorporation predicted by the simulations. These results demonstrate that structural compatibility between liquid-state structure and the target crystal motif governs selective incorporation during crystallization, providing a general kinetic mechanism by which compositional heterogeneity can emerge during growth of multicomponent crystals.
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All authors Rikuya Ishikawa, Kyohei Takae, Daisuke Takegami, Yoshikazu Mizuguchi, Rei Kurita

Materials Science · Cross-listed from cond-mat.soft

Evolution of Linear Viscoelasticity across the Critical Gelation Transition

Yogesh M Joshi

In this work, we develop a rigorous theoretical framework for the evolution of linear viscoelastic properties across the sol-gel transition. More specifically, we derive general admissible expressions for the relaxation modulus and dynamic moduli as the critical gel state is approached from the pre-gel or the post-gel side. These expressions possess a generalized multi-mode series representation and recover the critical gel power law spectrum in the limit of vanishing distance from the gel point. We validate these expressions against the experimental data for various polymeric and colloidal systems. A central finding of the present work is the requirement of continuity of the dynamic moduli and their derivatives at the critical gel point, which imposes a profound physical constraint, necessitating the relaxation dynamics on both sides of the transition to be symmetric. This, in turn, leads to the hyper-scaling relation, which is a theoretical requirement rather than an empirical proposal. We further show that the critical relaxation exponent (n) always remains above the relaxation scaling exponent (\kappa), establishing a previously unrecognized lower bound on n. We also analytically estimate, for the first time, the parameter C that characterizes the relative evolution of the storage modulus with respect to the loss modulus as the critical state is approached. These results reveal that the symmetry, scaling, and hyperscaling properties of the sol-gel transition are all consequences of a single unifying physical requirement originating from the continuity of the linear viscoelastic properties at the critical gel point.
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Materials Science

Composition-dependent bulk properties of intercalated transition metal dichalcogenides $Co_{1/3(1\pm\delta)}NbS_{2}$

Woonghee Cho, Kiwan Nam, Yeochan An et al. (+4 more)

We report a systematic study of the composition-dependent bulk properties in $Co_{1/3(1\pm\delta)}NbS_{2}$ single crystals across a series of precisely controlled cobalt compositions with -4%<$\delta$<8%. By tuning the cobalt stoichiometry, we find that the topological Hall effect is critically sensitive to the intercalant cobalt composition and is completely suppressed when the cobalt composition exceeds $\delta$=+4%. We observe that the longitudinal conductivity is also strongly influenced by the cobalt composition, reaching its maximum value just before the disappearance of the topological Hall effect. Furthermore, heat capacity measurements reveal distinct Sommerfeld coefficients ($\gamma$) across different compositions, which exhibit a clear linear scaling with the inverse of the ordinary Hall coefficient ($R_H^{-1}$). These results demonstrate that composition tuning in $Co_{1/3(1\pm\delta)}NbS_{2}$ systematically modifies the low-energy electronic degree of freedom, moving beyond a simple dilute impurity picture. Finally, we use the microscopic spin Hamiltonian to explain the stability of experimentally observed M-point modulation vector and the corresponding triple-Q magnetic order. Our findings highlight that the topological properties of this system are highly tunable through precise control of the intercalant concentration, offering a new perspective on the competition between electronic and magnetic orders in intercalated transition-metal dichalcogenides.
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All authors Woonghee Cho, Kiwan Nam, Yeochan An, You Young Kim, Myung-Hwa Jung, Kee Hoon Kim, Je-Geun Park

Materials Science

ZEBRA-Prop: A Zero-Shot Embedding-Based Rapid and Accessible Regression Model for Materials Properties

Ryoma Yamamoto, Akira Takahashi, Kei Terayama et al. (+2 more)

Large language models (LLMs) exhibit substantial potential across diverse scientific disciplines, including materials science. A property prediction framework, ZEBRA-Prop (Zero-Shot Embedding-Based Rapid and Accessible Regression Model for Materials Properties), is presented here as an extension of LLM-Prop. In contrast to LLM-Prop, which requires task-specific fine-tuning of the LLM, ZEBRA-Prop eliminates fine-tuning, thereby reducing computational cost and enabling rapid model training. The framework employs MatTPUSciBERT, an LLM specialized for materials science, to enhance predictive capability. Multiple textual embeddings are incorporated through a learnable weighting mechanism, which alleviates the context-length constraints inherent in LLM-Prop and facilitates effective integration of diverse textual representations. Evaluation is conducted using two datasets: the TextEdge dataset (approximately 140,000 entries) and an in-house dataset (approximately 2,000 entries) derived from the Materials Project database, with physical properties obtained from first-principles calculations. The predictive performance of ZEBRA-Prop is close to that of LLM-Prop, while the training time is reduced by approximately 95%. The performance improvements are attributable to three principal factors: domain-specific LLM utilization, diversified textual descriptions, and systematic text preprocessing. ZEBRA-Prop constitutes a scalable and computationally efficient framework for materials property prediction and supports accelerated materials discovery, particularly under limited computational resources.
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All authors Ryoma Yamamoto, Akira Takahashi, Kei Terayama, Yu Kumagai, Fumiyasu Oba

Materials Science

Computational Insights into PEMFC Durability: Degradation Mechanisms, Interfacial Chemistry, and the Emerging Role of Machine Learning Potentials

Jack Jon Hinsch and Kazushi Fujimoto

Proton exchange membrane fuel cells (PEMFCs) are a promising clean energy technology, offering high efficiency and near-zero operational emissions for stationery and automotive applications. However, their widespread adoption remains limited by insufficient durability, driven by the degradation of the catalyst layer and proton exchange membrane under realistic operating conditions. While the macroscopic consequences of degradation are well established experimentally, the atomistic and molecular mechanisms that initiate and propagate failure remain incompletely understood. This review synthesizes recent advances in computational modelling, spanning density functional theory, molecular dynamics, and emerging machine learning potentials, to examine how chemical, mechanical, electrochemical, and contamination driven degradation mechanisms operate across multiple length and time scales. Key topics include radical-induced membrane degradation, platinum dissolution and carbon support corrosion, mechanical fatigue under electrical and hygrothermal cycling, and the impact of ionic and gaseous contaminants. A central finding is that these degradation pathways are not independent, but form strongly coupled feedback loops that no existing computational framework has been designed to capture this coupling simultaneously. Future directions are proposed, with emphasis on multiscale modelling frameworks and the application of machine learning interatomic potentials to the electrified interface.
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Thursday 26 March

Materials Science · Cross-listed from eess.SP

Inference-Sufficient Representations for High-Throughput Measurement: Lessons from Lossless Compression Benchmarks in 4D-STEM

Ondrej Dyck, Andrew R. Lupini, Albina Borisevich et al. (+3 more)

Four-dimensional scanning transmission electron microscopy (4D-STEM) generates multi-gigabyte datasets, creating a growing mismatch between acquisition rates and practical storage, transfer, and interactive visualization capabilities. We systematically benchmark 13 lossless compression implementations across 5 representative datasets (8~MiB to 8~GiB, 49.5–92.8% sparsity), with 10 independent runs per method. HDF5 provides built-in gzip compression, of which gzip-9 typically achieves the highest compression ratio but is slow. We therefore evaluate widely available alternatives (via hdf5plugin), including the Blosc family. As a representative comparison, blosc\_zstd achieves compression comparable to gzip-9 (mean 13.5$\times$ vs 12.3$\times$) while compressing 19–69$\times$ faster and reading 1.9–2.6$\times$ faster across datasets. Compression ratios are deterministic, and timing measurements are highly reproducible (CV $<$2%). Compression performance follows a power law with sparsity ($R^2 = 0.99$), ranging from 5$\times$ for moderately sparse data to 35$\times$ for highly sparse data. We identify six top-performing implementations optimized for different use cases and demonstrate that 4D-STEM data can be routinely compressed by $>$10$\times$. While these results provide practical guidance for lossless compression selection, the broader conclusion is that lossless compression preserves measurements but does not by itself guarantee sustainable high-throughput workflows. As detector rates rise, data handling will increasingly require inference-driven representations – i.e., deciding what must be preserved to support a scientific inference, rather than defaulting to storing fully dense raw measurements.
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All authors Ondrej Dyck, Andrew R. Lupini, Albina Borisevich, Miaofang Chi, Rama K. Vasudevan, Stephen Jesse

Materials Science · Cross-listed from cs.MS

Multi-GPU fast Fourier transforms in MATLAB (for large-scale phase-field crystal simulations)

Maik Punke and Marco Salvalaglio

We present a MATLAB-based framework for two- and three-dimensional fast Fourier transforms on multiple GPUs for large-scale numerical simulations using the pseudo-spectral Fourier method. The software implements two complementary multi-GPU strategies that overcome single-GPU memory limitations and accelerate spectral solvers. This approach is motivated by and applied to phase-field crystal (PFC) models, which are governed by tenth-order partial differential equations, require fine spatial resolution, and are typically formulated in periodic domains. Our resulting numerical framework achieves significant speedups, approximately sixfold for standard PFC simulations and up to sixtyfold for multiphysics extensions, compared to a purely CPU-based implementation running on hundreds of cores.
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Materials Science · Cross-listed from cond-mat.soft

Entanglement by design: Symmetry-guided periodic helical assemblies

Myfanwy E. Evans

In this paper, a selection of elegant, highly symmetric examples of three-periodic tangled nets and filaments are presented. They are constructed via familiar crystal nets using edges as geometric scaffolds for n-fold helical windings. Rather than providing a complete classification, this gallery of examples highlights recurring geometric motifs, offering insight into how periodic tangles are organised in crystalline, molecular, and biological systems.
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Materials Science

Modeling key characteristics of high-efficiency gallium arsenide solar cells

A.V. Sachenko, V.P. Kostylyov, I.O. Sokolovskyi et al. (+1 more)

The paper proposes a theoretical approach to modeling the key characteristics of highly efficient gallium arsenide-based solar cells (SCs), using a one-dimensional SC model. The following recombination mechanisms are considered in the modeling: radiative recombination, interband Auger recombination, Shockley-Reed-Hall (SRH) recombination, surface recombination, recombination in the space charge region (SCR), and recombination along the perimeter of the structure. A simple empirical formula is proposed to describe the recombination along the perimeter of the SC structure. The GaAs band-gap narrowing effect is also taken into consideration. The main results are obtained under the assumption that the times of Shockley-Reed-Hall recombination and recombination in the SCR are the same. The effect of photon recycling (re-emission and re-absorption) is taken into account in a model similar to the one we used previously to simulate key characteristics of high-efficiency single-crystal silicon SCs. The model additionally uses absorption analysis at different doping levels of gallium arsenide. A good agreement was achieved between the experimental and theoretical dependencies. The results obtained in this work can be used to optimize the characteristics of highly efficient SCs based on direct-band semiconductors, particularly gallium arsenide (GaAs). Keywords: solar cell, high efficiency, modeling, gallium arsenide, recombination mechanisms, external quantum efficiency, parameter optimization.
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All authors A.V. Sachenko, V.P. Kostylyov, I.O. Sokolovskyi, A.I. Shkrebtii

Materials Science

Exciton dynamics and high-temperature excitonic superfluidity in S-doped graphyne

Enesio Marinho Jr., Alexandre C. Dias, Luiz A. Ribeiro Jr. et al. (+2 more)

S-doped graphyne (S-GY) is a recently synthesized two-dimensional graphyne-based carbon allotrope that provides a promising platform for exciton engineering and coherent many-body phases. Here, we investigate the quasiparticle electronic structure, optical response, and exciton dynamics of monolayer S-GY using the G$_0$W$_0$ approximation and the Bethe–Salpeter equation (BSE). Quasiparticle corrections increase the fundamental band gap from $0.88\,\text{eV}$ (PBE) to $1.95\,\text{eV}$, while slightly reducing the carrier effective masses. The BSE optical response reveals strongly bound excitons, with the lowest bright exciton exhibiting a binding energy of $0.72\,\text{eV}$, as well as a nearly degenerate dark exciton within the thermal energy scale. Analysis of exciton wavefunctions in reciprocal space confirms a hydrogenic Rydberg series with well-defined angular-momentum character, and radiative lifetimes in the nanosecond range at room temperature, comparable to those in transition-metal dichalcogenide monolayers. Finally, we construct the excitonic phase diagram and estimate a crossover density of $\sim6 \times10^{12}~\text{cm}^{-2}$, below which the exciton gas behaves as a dilute Bose system, and the Berezinskii–Kosterlitz–Thouless (BKT) superfluid phase becomes accessible. We estimate a maximum BKT transition temperature of $\sim 143\,\text{K}$ in the freestanding limit for the 1s exciton, indicating that monolayer S-GY may provide favorable conditions for high-temperature excitonic superfluidity in graphyne-based materials.
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All authors Enesio Marinho Jr., Alexandre C. Dias, Luiz A. Ribeiro Jr., Maurizia Palummo, Cesar E. P. Villegas

Materials Science

Room-temperature antiferromagnetic resonance in NaMnAs

Jan Dzian, Stáňa Tázlarů, Ivan Mohelský et al. (+16 more)

We report on antiferromagnetic resonance experiments in bulk tetragonal NaMnAs – a room-temperature antiferromagnetic semiconductor. Our results corroborate previous ab initio studies, which propose that NaMnAs is an easy-axis antiferromagnet with the Néel vector oriented along the tetragonal axis. At $ B = 0 $, we find a single antiferromagnetic resonance line at 7 meV and associate it with a doubly degenerate ($ k = 0 $) magnon mode. Its energy softens considerably with increasing $ T $, but remains clearly visible in the data up to room temperature. From the experimental data, we estimate the single-ion anisotropy of the Mn ions in NaMnAs in the range 0.1-0.2 meV, a value that is relatively large compared to other manganese-based antiferromagnets.
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All authors Jan Dzian, Stáňa Tázlarů, Ivan Mohelský, Florian Le Mardelé, Filip Chudoba, Jiří Volný, Jan Wyzula, Amit Pawbake, Simone Ritarossi, Riccardo Mazzarello, Philipp Ritzinger, Jakub Železný, Karel Výborný, Klára Uhlířová, Benoît Grémaud, Andrés Saúl, Clément Faugeras, Martin Veis, Milan Orlita

Materials Science

Cluster glass behavior and magnetocaloric effect in the hexagonal polymorph of disordered Ce$_2$PdGe$_3$

Leszek S. Litzbarski, Kamil Balcarek, Anna Bajorek et al. (+3 more)

In this work, we study the hexagonal variant of the $\text{Ce}_2\text{PdGe}_3$ system that crystallizes in the $\text{AlB}_2$-type structure (space group $P6/mmm$, $hP3$) and exhibits cluster spin glass type behavior. The physical properties were studied by magnetization, heat capacity and electric resistivity, which showed that $\text{AlB}_2$-type $\text{Ce}_2\text{PdGe}_3$ ($h\text{-Ce}_2\text{PdGe}_3$) can be classified as a cluster glass material with the freezing temperature $T_f = 3.44 \text{ K}$ in contrast to the behavior of the previously described tetragonal variant, which shows a double antiferromagnetic transition at $T_{N1} = 11 \text{ K}$ and $T_{N2} = 2.3 \text{ K}$. The X-ray photoelectron spectroscopy measurements reveal that the $\text{Ce } 4f$ states are well localized. In addition, we examine the magnetocaloric effect in this compound. The maximum values of magnetocaloric parameters appear in the vicinity of $7\text{--}9 \text{ K}$. For a magnetic field change of $50 \text{ kOe}$, the value of the change in magnetic entropy is $2.6(1) \text{ J kg}^{-1} \text{ K}^{-1}$ and the adiabatic temperature change is $\sim 8 \text{ K}$.
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All authors Leszek S. Litzbarski, Kamil Balcarek, Anna Bajorek, Tomasz Klimczuk, Michał J. Winiarski, Karol Synoradzki

Materials Science

Compositional Complexity-Induced Ultralow Friction in Medium-Entropy MXenes

Jiaoli Li, Yuwei Zhang, Congjie Wei et al. (+11 more)

Two-dimensional MXenes are promising solid lubricants, but the roles of compositional complexity and surface chemistry in governing interfacial friction remain unclear. Here, we systematically investigate the adhesion and friction behaviors of medium-entropy (ME) MXenes, TiVNbMoC3 and TiVCrMoC3, and compare them with conventional titanium carbide MXenes, Ti2C and Ti3C2, using a SiO2 colloidal atomic force microscopy probe. Thermal annealing at 200 C converts OH surface terminations to O terminations, leading to pronounced reductions in adhesion energy and friction force across all MXenes studied. ME MXenes exhibit larger adhesion reductions because of their higher initial OH contents and more extensive OH-to-O conversion. In addition, their intrinsically higher out-of-plane bending stiffness suppresses energy dissipation during sliding, enabling ultralow friction. Notably, superlubricity is achieved in ME MXenes, with annealed TiVCrMoC3 exhibiting a coefficient of friction as low as 0.0022, outperforming graphene, MoSe2, and other MXenes evaluated using the same experimental approach. These findings identify compositional complexity as a powerful strategy for engineering MXenes with exceptional tribological performance and establish ME MXenes as a new class of solid lubricants.
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All authors Jiaoli Li, Yuwei Zhang, Congjie Wei, Yanxiao Li, Shuo He, Risheng Wang, Brian Wyatt, Reza Namakian, Babak Anasori, Kelvin Xie, Tobin Filleter, Ali Erdemir, Wei Gao, Chenglin Wu

Materials Science

Decoupling dislocation multiplication and velocity effects in metals at extreme strain rates

Daniyar Syrlybayev, Lavanya Raman, Niraj Pramod Atale et al. (+4 more)

The dynamic behavior of metals is governed by collective dislocation motion and interactions that strongly depend on the applied strain rate. Metals exhibit weak strain rate sensitivity (SRS) below a certain threshold, followed by a distinct SRS upturn at higher loading rates. While this upturn is typically attributed to increased glide resistance at high dislocation velocity due to mechanisms such as phonon drag, the role of strain-rate-dependent dislocation multiplication and microstructural evolution under these extreme conditions remains elusive. Here, we decouple these two strengthening effects and show that, while dislocation velocity primarily governs the SRS upturn, the hardening due to microstructure evolution depends strongly on the initial dislocation density. Our investigation of hardness evolution across ten decades of strain rates in a quenched and tempered martensitic low-carbon steel (LCS) using laser-induced projectile impact tests (LIPIT) and nanoindentation reveals SRS upturn around 10^7 1/s. By performing in situ re-indentation of the formed craters, we probe the contribution of dislocations generated during initial deformation at different strain rates. We show that while dislocation multiplication plays a negligible role in fine-grained LCS with high dislocation density, a pronounced dislocation multiplication contributes to the hardness increase in pure iron with lower initial dislocation density. Our results show that, depending on the initial microstructure of metals, dislocation multiplication significantly governs high-strain-rate plasticity, in addition to dislocation velocity effects.
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All authors Daniyar Syrlybayev, Lavanya Raman, Niraj Pramod Atale, Bhanugoban Maheswaran, Siddhartha Pathak, Curt A. Bronkhorst, Ramathasan Thevamaran

Materials Science

Universal effect of ammonia pressure on synthesis of colloidal metal nitrides in molten salts

Ruiming Lin, Vikash Khokhar, Ningxin Jiang et al. (+11 more)

Metal nitrides represent a large class of materials with extensive applications in optoelectronics, energy, and healthcare technologies. For example, GaN and related nitride semiconductors are key materials for solid-state lighting and high-power electronics, TiN and other early transition metal nitrides (TMNs) are widely used in wear-resistant alloys, tool coatings, catalysts and medical implants. Strong metal-nitrogen bonds grant nitrides structural rigidity as well as chemical and thermal stability. However, the covalency of metal-nitrogen bonds necessitates high temperatures to synthesize crystalline metal nitrides. Common synthetic routes include high-temperature solid-state nitridation, crystal growth in supercritical ammonia, molecular-beam epitaxy (MBE), reactive sputtering, and chemical vapor deposition (CVD). The solution synthesis of colloidal nitride nanocrystals (NCs) is rare and particularly challenging because commonly used solvents and surfactants decompose at temperatures far below those required for crystallization of most metal nitrides. Here we report a general approach to solution synthesis of colloidal metal nitride NCs by reacting metal halides and ammonia dissolved in molten inorganic salts at elevated pressures. Successful syntheses of colloidal TiN, VN, GaN, NbN, Mo2N, Ta3N5, W2N, as well as ternary Ti1-xVxN NCs, are demonstrated. These NCs expand the scope of solution-processable technologically important materials.
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All authors Ruiming Lin, Vikash Khokhar, Ningxin Jiang, Wooje Cho, Zirui Zhou, Di Wang, Justin C. Ondry, Zehan Mi, James Cassidy, Alex M. Hinkle, John S. Anderson, Richard D. Schaller, De-en Jiang, Dmitri V. Talapin

Materials Science

Electrical and thermal magnetotransport in altermagnetic CrSb

Sajal Naduvile Thadathil, Christoph Müller, Reza Firouzmandi et al. (+20 more)

Chromium antimonide has emerged as a key material platform for studying altermagnetism because of its simple binary composition, high Néel temperature, and semimetallic electronic structure. Here, we investigate electrical and thermal magnetotransport in single-crystalline CrSb using steady-and pulsed-magnetic fields up to 65 T, and complement these measurements with neutron diffraction and magnetization data. We confirm the compensated magnetic structure and observe a large nonsaturating magnetoresistance together with a pronounced nonlinear Hall response at low temperatures. Multicarrier modeling, supported by mobility-spectrum analysis, reveals coexisting electron- and hole-like charge carriers with mobilities up to ~3000 cm2/Vs and shows that the number of transport channels that can be resolved strongly depends on the accessible magnetic-field range. Thermal-transport measurements further reveal a nonlinear thermal Hall response and a thermal conductivity substantially exceeding a simple Wiedemann-Franz law. The broadly similar field and temperature evolution of electrical and thermal transport point to a dominant electronic contribution, while the remaining deviations indicate additional heat-carrying channels.
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All authors Sajal Naduvile Thadathil, Christoph Müller, Reza Firouzmandi, Lorenz Farin, Srikanta Goswami, Antonin Badura, Pascal Manuel, Fabio Orlandi, Philipp Ritzinger, Václav Petříček, Marc Uhlarz, Tommy Kotte, Michal Baj, Marein C. Rahn, Thanassis Speliotis, Markéta Žáčková, Jiří Pospíšil, Bernd Büchner, Jochen Wosnitza, Helena Reichlová, Vilmos Kocsis, Toni Helm, Dominik Kriegner

Materials Science · Cross-listed from cond-mat.str-el

Magnetism and magnetoelastic effect in 2D van der Waals multiferroic CuCrP2S6

Jiasen Guo, Ryan P. Siebenaller, Michael A. Susner et al. (+3 more)

We report a magnetic and neutron diffraction study on the ground state magnetism and field evolution of single crystal van der Waals multiferroic CuCrP2S6. The ordered moments align along the b axis in the A-type antiferromagnetic configuration with a spin-flop transition along the same direction. Field application along a introduces a smooth transition to a fully-polarized ferromagnetic state via in-plane spin rotation. These findings resolve the ambiguity of the ground state magnetization direction in CuCrP2S6 and uncover its field responses, providing a firm basis for future magnetoelectric study. A magnetoelastic coupling effect connecting the interlayer spacing and the magnetic order was further revealed, highlighting the out-of-plane strain as an effective control knob for tuning magnetism both in this system and in related van der Waals magnets.
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All authors Jiasen Guo, Ryan P. Siebenaller, Michael A. Susner, Jiaqiang Yan, Zachary Morgan, Feng Ye

Materials Science

Suppressed excitonic effects enable high mobility, high-yield photoconductivity in a two-dimensional polymer crystal with axial pyridine coordination

Shuai Fu, Ye Yang, Guoquan Gao et al. (+8 more)

Two-dimensional polymers (2DPs) and their layer-stacked covalent organic frameworks (2D COFs) offer modular, atomically precise platforms for organic optoelectronics, yet their photoconductive responses remain fundamentally constrained by strong excitonic effects and localized charge transport. Here, we demonstrate that a diyne-linked 2DP crystal with axial pyridine coordination overcomes this limitation, enabling simultaneous efficient free-carrier generation and band-like transport. Introducing pyridine ligands that axially coordinate to Cu-porphyrin nodes transforms weak van der Waals stacking into a pyridine-bridged architecture with pronounced interlayer band dispersion and substantially reduced carrier effective masses. The resulting strong interlayer electronic coupling suppresses the exciton binding energy to well below thermal energy, such that optical excitation directly populates delocalized electronic states. Time-resolved terahertz spectroscopy reveals Drude-type photoconductivity with room-temperature mobilities approaching 500 cm^2 V^-1 s^-1 and a photon-to-free-carrier conversion ratio of ~0.4, yielding a photoconductive response that exceeds that of state-of-the-art organic and many inorganic photoactive materials. These results establish interlayer coordination as a powerful strategy for mitigating excitonic effects and accessing inorganic-like charge transport in organic 2D crystals, opening a pathway toward highly efficient photo-to-electricity conversion in organic-based systems.
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All authors Shuai Fu, Ye Yang, Guoquan Gao, Shuangjie Zhao, Miroslav Položij, Tong Zhu, Lei Gao, Thomas Heine, Zhiyong Wang, Mischa Bonn, Xinliang Feng

Materials Science · Cross-listed from cs.CV

Evaluating Synthetic Images as Effective Substitutes for Experimental Data in Surface Roughness Classification

Binwei Chen, Huachao Leng, Chi Yeung Mang et al. (+5 more)

Hard coatings play a critical role in industry, with ceramic materials offering outstanding hardness and thermal stability for applications that demand superior mechanical performance. However, deploying artificial intelligence (AI) for surface roughness classification is often constrained by the need for large labeled datasets and costly high-resolution imaging equipment. In this study, we explore the use of synthetic images, generated with Stable Diffusion XL, as an efficient alternative or supplement to experimentally acquired data for classifying ceramic surface roughness. We show that augmenting authentic datasets with generative images yields test accuracies comparable to those obtained using exclusively experimental images, demonstrating that synthetic images effectively reproduce the structural features necessary for classification. We further assess method robustness by systematically varying key training hyperparameters (epoch count, batch size, and learning rate), and identify configurations that preserve performance while reducing data requirements. Our results indicate that generative AI can substantially improve data efficiency and reliability in materials-image classification workflows, offering a practical route to lower experimental cost, accelerate model development, and expand AI applicability in materials engineering.
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All authors Binwei Chen, Huachao Leng, Chi Yeung Mang, Tsz Wai Cheung, Yanhua Chen, Wai Keung Anthony Loh, Chi Ho Wong, Chak Yin Tang

Materials Science

Electrostatic Photoluminescence Tuning in All-Solid-State Perovskite Transistors

Vladimir Bruevich, Dmitry Maslennikov, Beier Hu et al. (+2 more)

We demonstrate an all solid state semiconductor device, based on epitaxial single crystalline metal halide perovskites, enabling reversible control of a perovskite photoluminescence with a gate voltage. Fundamentally distinct from electroluminescent diodes, such a photoluminescence field effect transistor uses the gate electric field to electrostatically modulate the interfacial density of mobile charges, thereby affecting the radiative and nonradiative recombination channels of photocarriers. Varying the gate voltage in such transistors efficiently changes the rate of nonradiative interfacial recombination and modulates the photoluminescence intensity by 65 to 98 percent (depending on temperature). At favorable gating, nearly complete elimination of non-radiative losses can be achieved. This functionality, coupled with the strong visible-range absorption and emission, possible due to the high absorption coefficient, as well as controllable thickness and macroscopically homogeneous morphology of epitaxial perovskite films, leads to high external photoluminescence quantum efficiencies realized in large-area, thin-film devices. Such high-efficiency, scalable, electrostatically tunable optoelectronic switches broaden the potential applications of metal-halide perovskites in photonics and optoelectronics.
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All authors Vladimir Bruevich, Dmitry Maslennikov, Beier Hu, Artem A. Bakulin, Vitaly Podzorov

Materials Science · Cross-listed from math.NA

A Quasicontinuum Method with Optimized Local Maximum-Entropy Interpolation and Heaviside Enrichment for Heterogeneous Lattices

Benjamin Werner, Ondřej Rokoš and Jan Zeman

Lattice systems are effective for modeling heterogeneous materials, but their computational cost is often prohibitive. The QuasiContinuum (QC) method reduces this cost by interpolating the lattice response over a coarse finite-element mesh, yet material interfaces in heterogeneous systems still require fine discretizations. Enrichment strategies from the eXtended Finite Element Method (XFEM) address this by representing interfaces on nonconforming meshes. In this work, we combine Heaviside enrichment with meshless Local Maximum Entropy (LME) interpolation in the QC framework for heterogeneous lattice systems. We systematically investigate the role of the LME locality parameter and its optimization. The results show that optimized LME interpolation improves displacement accuracy by about one order of magnitude over QC with linear interpolation at the same number of degrees of freedom. In addition, the optimal locality-parameter fields are nonuniform near interfaces and exhibit systematic spatial structure. Based on these observations, we derive simple pattern-based rules that retain much of the benefit of full optimization at a fraction of the computational cost. The approach is demonstrated on three numerical examples.
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Materials Science

Interfacial Polytype Engineering of Polymer-Derived SiC via Compositionally Complex MXene Templating

Yuxiang Gan, Jianyu Dai, Laxmi Sai Viswanadha et al. (+5 more)

Controlling polytype selection in polymer-derived silicon carbide (SiC) remains challenging since stacking sequences are determined locally at the nucleation front. Here, we demonstrate an interface-driven strategy to bias SiC polytype evolution by introducing compositionally complex TiVCrMoC3 MXene nanosheets at the preceramic stage. Under spark plasma sintering (1900 C, 70 MPa), which typically stabilizes cubic beta-SiC, the MXene partially transforms into multicomponent carbide structures and generates two distinct heterogeneous interfacial states: reconstructed carbide/SiC interfaces that locally disrupt stacking sequences and promote hexagonal ordering, driving the emergence of alpha-SiC; and coherent MXene/SiC interfaces that preserve cubic stacking. Mechanical testing further reveals peak performance at an optimal MXene loading where interfacial reconstruction is most pronounced, with an around 82% increase in Young's modulus and 42% improvement in fracture toughness. These findings highlight interfacial polytype engineering via two-dimensional carbide templates as a promising route for directing crystal structure evolution in polymer-derived ceramics.
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All authors Yuxiang Gan, Jianyu Dai, Laxmi Sai Viswanadha, Congjie Wei, Kelvin Y. Xie, Jeremy Watts, Mohammad Naraghi, Chenglin Wu

Materials Science · Cross-listed from cond-mat.supr-con

Prediction of new superconducting bilayers heterostructures using quantum confinement and proximity effects

Giovanni A. Ummarino and Alessio Zaccone

A central challenge in nanoscale superconductivity is to understand and exploit the combined action of quantum confinement and proximity effects in experimentally realistic metallic heterostructures. We theoretically investigate superconducting bilayer heterostructures in which these two effects coexist. Using a generalized Eliashberg framework that incorporates both quantum confinement and proximity coupling, we show that their interplay can substantially enhance the superconducting critical temperature. In particular, the theory predicts superconductivity in selected bilayers whose constituent materials are nonsuperconducting or only weakly superconducting in the bulk. These results identify quantum-confined bilayers as a promising route to engineering emergent superconductivity in metallic heterostructures.
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Materials Science · Cross-listed from physics.flu-dyn

Converting vertical heat supply into horizontal motion for microtechnological pumping and autonomous waste heat recovery

Jan-Niklas Schäfer, Tillmann Carl, Kristin Kühl et al. (+4 more)

The rapid advancement of high-performance computing infrastructure and its extended application produce an increasing amount of waste heat. This heat constitutes an unsustainable loss of energy as well as requires cooling solutions that transcend conventional thermal management. Here, we demonstrate a novel mechanism that converts vertical waste heat supply directly into horizontal fluid motion, enabling autonomous, self-powered pumping in microenvironments. Our approach is based on a concept that combines geometric symmetry breaking with heterogeneous thermal conductivities to induce local thermocapillary Marangoni flows. We provide an implementation of the concept as well as an experimental and numerical proof-of-concept, showing good agreement between the respective flow fields. The approach is scalable and operates under realistic areal heating conditions. It enables versatile pumping designs for microtechnological applications, lab-on-a-chip architectures, passive thermal management and heat-driven microfluidic systems.
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All authors Jan-Niklas Schäfer, Tillmann Carl, Kristin Kühl, Sonja Kiehren-Ehses, Jan Aurich, Georg von Freymann, Clarissa Schönecker

Materials Science

Growth and Kerr magnetometry of Mn2Au on a gold-capped Nb(001) substrate

Jendrik Gördes, Christian Janzen, Arne J. Vereijken et al. (+4 more)

We report on the epitaxial growth of antiferromagnetic Mn2Au on a Nb(001) substrate capped with a pseudomorphic layer of gold. We observe a layer-by-layer growth by means of medium-energy electron diffraction and confirm stoichiometry and surface structure by Auger electron spectroscopy and low-energy electron diffraction. Evaporation of 15 ML of ferromagnetic Fe on 12–17 ML of Mn2Au results in an exchange-coupled bilayer system with an exchange-bias shift that can be set by field-cooling from 400 K. Areas with and without exchange bias, with domain sizes in the range of tens of {\mu}m, are identified by Kerr microscopy. Postannealing the sample at or above 450 K after Mn2Au layer growth decreases the amount of areas where Fe magnetically couples to Mn2Au. We conclude that exchange coupling to an interfacial Fe layer depends on the interface termination of Mn2Au. Our findings provide insight into the growth process of Mn2Au and the coupling to an Fe layer. Our results point out the importance of growth, interface quality and termination on the magnetic properties of a Mn2Au/Fe bilayer which may help to improve material properties for spintronic applications.
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All authors Jendrik Gördes, Christian Janzen, Arne J. Vereijken, Tingwei Li, Tauqir Shinwari, Arno Ehresmann, Wolfgang Kuch

Materials Science

Molecular dynamics study of the role of anisotropy in radiation-driven embrittlement

Hojjat Mousavi, Stanisław Stupkiewicz and Aneta Ustrzycka

This study investigates the influence of crystallographic orientation on fracture behavior and the resulting mechanical anisotropy in a Fe55Ni19Cr26 alloy crystal containing radiation-induced defects, using molecular dynamics (MD) simulations. Crack propagation is analyzed in irradiated samples with three selected high-symmetry crystallographic orientations to show how radiation-induced defects modify local deformation mechanisms and amplify mechanical anisotropy. The investigation focuses on the anisotropic nature of the ductile-to-brittle transition (DBT) driven by radiation-induced defects by simulating fracture behavior under tensile loading. Fracture resistance is quantitatively evaluated using a traction-separation (T-S) approach to extract the atomic-scale fracture energy under realistic defect conditions. The results reveal a strong crystallographic orientation dependence in the evolution of deformation and fracture behavior during DBT. The crystal lattice orientation governs dislocation activity and defect interactions, which in turn regulate local plasticity mechanisms, strain localization, slip system activation, and fracture resistance, thereby driving the development and enhancement of mechanical anisotropy in irradiated materials. It is further shown that radiation-induced embrittlement cannot be explained solely by defect accumulation, but rather by orientation-sensitive interactions among dislocations, defects, and fracture process zones. A key novelty of this work lies in integrating radiation-induced defect evolution with orientation-dependent fracture within an atomistic T-S analysis, enabling quantitative assessment of atomic-scale fracture resistance under realistic defect conditions.
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Materials Science

General-Purpose Machine-Learned Potential for CrCoNi Alloys Enabling Large-Scale Atomistic Simulations with First-Principles Accuracy

Yong-Chao Wu, Tero Mäkinen, Mikko Alava et al. (+1 more)

CrCoNi medium-entropy alloys exhibit exceptional mechanical properties arising from pronounced chemical complexity, including short-range order (SRO), and low stacking fault energy, posing challenges for large-scale atomistic simulations. While most models focus on equimolar compositions, deviations from equimolarity provide an effective route to tuning properties, requiring transferable interatomic potentials that capture composition-dependent behavior. Here we develop a general-purpose machine-learned interatomic potential for the CrCoNi system within the neuroevolution potential (NEP) framework, achieving near first-principles accuracy with high computational efficiency. Trained on a comprehensive dataset spanning pure elements, binary and ternary alloys across a wide compositional range, diverse crystal structures and thermodynamic conditions, and based on spin-polarized ab initio data, the model accurately reproduces equations of state, phonons, elastic constants, dislocation dissociation, surface and defect energies, melting temperatures and strain-induced phase transformations. It further captures SRO and its effect on stacking fault energies across both equimolar and non-equimolar compositions, in agreement with first-principles and experiments. In contrast to existing potentials, typically limited to equimolar alloys and less accurate for pure elements, the present model delivers consistent accuracy across the full compositional space while retaining superior efficiency. These results enable reliable atomistic simulations of composition-dependent behaviour and provide a framework for the design of non-equimolar CrCoNi alloys.
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All authors Yong-Chao Wu, Tero Mäkinen, Mikko Alava, Amin Esfandiarpour

Materials Science

Single Atom Magnets on Thermally Stable Adsorption Sites: Dy on NaCl(100)

M. Pivetta, M. Blanco-Rey, S. Reynaud et al. (+14 more)

We report magnetic bistability in single Dy atoms on NaCl(100) thin films. Individual Dy atoms substituting Na at the surface of the NaCl layer are thermally stable up to at least 300 K, display $4f^{9}$ occupancy, out-of-plane easy magnetization axis, and long spin relaxation time $T_1$ of about 10 s at 2.5 K; thereby they are the first single atom magnet on a thermally stable adsorption site. Dy atoms adsorbed onto the Cl and bridge sites display $4f^{10}$ occupancy. Dy on top-Cl exhibit magnetic hysteresis and a $T_1$ of 550 s at 0.3 T and 2.5 K. The observed slow magnetic relaxation of Dy on both adsorption sites introduces NaCl as an effective platform for single atom magnets.
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All authors M. Pivetta, M. Blanco-Rey, S. Reynaud, R. Baltic, A. Rary-Zinque, S. Toda Cosi, F. Patthey, B. V. Sorokin, A. Singha, F. Donati, A. Barla, L. Persichetti, P. Gambardella, A. Arnau, F. Delgado, S. Rusponi, H. Brune

Materials Science

Revealing the Atomic-Scale Structure of the Copper Sulfuric Acid Interface

Lalith Kumar Bhaskar, Sung-Gyu Kang, Oliver R. Waszkiewicz et al. (+7 more)

Corrosion originates from atomistic reactions occurring at dynamic solid liquid interfaces however, direct experimental observation of these reactions has remained elusive due to the inability to preserve transient interfacial states during characterization. To refine corrosion models, advanced techniques capable of analyzing corrosion interfaces at the atomic scale are essential. Recent advancements in cryogenic atom probe tomography (cryoAPT) enabled 3D nanoscale analysis of frozen liquid metal interfaces. However, challenges remain in sample preparation for cryoAPT on metals undergoing corrosion. This study introduces a microcorrosion cell fabricated using localized electrodeposition in liquid (LEL), enabling atomic scale capture of liquid metal reactions by integrating picoliterscale electrolytes encapsulated within sealed metallic microvessels, subsequently analyzed using cryoAPT.This approach enables 3D, nanoscale mapping of corrosion reactions with simultaneous spatial, chemical, and temporal resolution. As a model system, copper exposed to aerated dilute sulphuric acid reveals temperature and time dependent interfacial evolution, including nanoscale clustering of copper sulphate species, enhanced ion pairing at elevated temperature, and the emergence of transient carbon based interfacial complexes inaccessible to conventional characterization methods.Beyond copper corrosion, the presented microcorrosion cell architecture establishes a strategy for interrogating confined electrochemical and degradation processes across a wide range of material liquid systems, using a combination of microfabrication and cryoAPT.
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All authors Lalith Kumar Bhaskar, Sung-Gyu Kang, Oliver R. Waszkiewicz, Finn Giuliani, Baptiste Gault, Mary P. Ryan, Roger C. Newman, Gerhard Dehm, Rajaprakash Ramachandramoorthy, Ayman A. El-Zoka

Materials Science

Anisotropic light-electron-phonon coupling and ultrafast carrier separation in ferroelectric BaTiO$_3$

Atal Bihari Swain, Somnath Kale, Rohit Soni et al. (+1 more)

Ferroelectric materials with built-in electric fields are useful for ultrafast electronics and conversion of light into electrical energy, yet the interaction of carrier motion with ultrafast relaxation processes remains nontrivial. Combining ultrafast electron diffraction with electron microscopy of electromagnetic fields, we capture ultrafast lattice dynamics and nanometer-scale carrier transport in ferroelectric BaTiO$_3$. We discover that BaTiO$_3$ reacts to light with an anisotropic electron-phonon coupling that depends on the optical polarization of the excitation light. Excited electrons relax two times faster into phonons when the optical electric field aligns to the ferroelectric symmetry break. Furthermore, ultrafast electron electrometry captures the motion and separation of photo-excited electron-hole pairs in the presence of the ferroelectric field. These combined results provide insight into the tangled and anisotropic interaction of photons with phonons and the ferroelectric field, producing phonons and voltages in a stepwise reaction path.
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All authors Atal Bihari Swain, Somnath Kale, Rohit Soni, Peter Baum