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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Tuesday 14 October

Materials Science

Spectroscopic Determination of Site-Selective Ligand Binding on Single Anisotropic Nanocrystals

Dong Le, Wade Shipley, Alexandria Do et al. (+17 more)

Organic surface ligands are integral components of nanocrystals and nanoparticles that have a strong influence on their physicochemical properties, their interaction with the environment, and their ability to self-assemble and order into higher-order structures. These hybrid nanomaterials are tunable with applications in catalysis, directed self-assembly, next-generation optoelectronics, and chemical and quantum sensing. Critically, future advances depend on our ability to rationally engineer their surface chemistry. However, fundamental knowledge of ligand-nanoparticle behavior is limited by uncertainty in where and how these ligands bind to surfaces. For nanoparticles, in particular, few characterization techniques offer both the high spatial resolution and the precise chemical mapping needed to identify specific ligand binding sites. In this study, we utilized synchrotron infrared nanospectroscopy (SINS), atomic force microscopy (AFM), and scanning tunneling microscopy (STM) together with first-principles computer simulations to validate the site-selective adsorption of organic ligands on a shaped nanocrystal surface. Specifically, we demonstrate that the sterically encumbered isocyanide ligands (CNAr^{Mes2}) preferentially bind to the high curvature features of Ag nanocubes (NCs), where low-coordinate Ag atoms are present. In contrast, isocyanide ligands that do not exhibit these steric properties show no surface selectivity. SINS serves as an effective tool to validate these surface binding interactions at the near-single molecule level. These results indicate that steric effects can be successfully harnessed to design bespoke organic ligands for fine-tuning nanocrystal surface chemistry and the properties of the nanocrystal ligand shell.
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All authors Dong Le, Wade Shipley, Alexandria Do, Liya Bi, Yufei Wang, Krista P. Balto, Rourav Basak, Hans A. Bechtel, Stephanie N. Gilbert Corder, Ilya Mazalov, Tesa Manto, Reno Sammons, Yutong She, Fiona Liang, Ganesh Raghavendran, Joshua S. Figueroa, Shaowei Li, Tod A. Pascal, Andrea R. Tao, Alex Frano

Materials Science · Cross-listed from cond-mat.mes-hall

Trembling motion of electrons driven by Larmor spin precession

I. Stepanov, M. Ersfeld, A. V. Poshakinskiy et al. (+4 more)

We show that the initialization of an ensemble of electrons in the same spin state in strained n-InGaAs subject to a perpendicular magnetic field triggers an AC electric current at GHz frequencies. The AC current emerges in the absence of any driving force and survives until the coherent precession of the electron spins is lost. The current amplitude increases linearly with both the spin-orbit coupling strength and the external magnetic field. The generation mechanism of the observed oscillatory charge motion can be fruitfully described in terms of the periodic trembling motion of spin-polarized electrons, which is a solid-state analog to the Zitterbewegung of free Dirac electrons. Our results demonstrate that the hidden consequence of relativistic quantum mechanics is realized and can be studied in a rather simple solid-state system at moderate temperatures. Furthermore, the large amplitude of the AC current at high magnetic fields enables ultra-fast spin sensitive electric read-out in solids.
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All authors I. Stepanov, M. Ersfeld, A. V. Poshakinskiy, M. Lepsa, E. L. Ivchenko, S. A. Tarasenko, B. Beschoten

Materials Science

Nanoscale surface morphology controls charge storage at stepped Pt-water interfaces

Matthew T. Darby, Muhammad Saleh, Marialore Sulpizi et al. (+1 more)

Platinum step edges dominate electrocatalytic activity in fuel cells and electrolysers, yet their atomistic electrochemical behaviour remains poorly understood. Here, we employ ab initio molecular dynamics under controlled electrode potentials to model a realistic stepped Pt–water interface incorporating experimentally observed (111)$\times$(111) and (111)$\times$(100) edge motifs. This allows us to resolve, for the first time, the site-specific structure, charge distribution, and electrostatics of the electric double layer at a nanostructured Pt surface. We find that differential capacitance near the potential of zero charge (PZC) arises almost entirely from potential-dependent chemisorption of water on flat (111) terraces. In contrast, step edges are saturated with chemisorbed water even below the PZC and thus do not contribute to the capacitance. Instead, edges accumulate excess positive charge and exhibit a locally elevated electrostatic potential, as revealed by spatially resolved macroscopic potential profiles. This electrostatic asymmetry implies a greater barrier for electron accumulation at step sites compared to terraces, consistent with enhanced charge localisation and reactivity. Finally, the higher-in-energy d-band centre and sharper projected density of states at edge atoms further support their role as active, positively charged centres. Together, these results provide a mechanistic explanation for the observed experimental shift of the PZC with step density and establish a predictive framework for understanding and optimising interfacial charging in nanostructured Pt electrocatalysts.
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All authors Matthew T. Darby, Muhammad Saleh, Marialore Sulpizi, Clotilde S. Cucinotta

Materials Science

Chern-Selective multi-valley Flat Bands in Twisted Mono-Bilayer and Mono-Trilayer MoTe$_2$

Ziyue Qi, Hanqi Pi, Yan Zhang et al. (+6 more)

The interplay between moiré flat bands originating from different valleys can give rise to a variety of exotic quantum phases. In this work, we investigate the electronic properties of twisted mono-bilayer (A-AB) and mono-trilayer (A-ABA) MoTe$_2$ using first-principles calculations and continuum models. Unlike previous studies on twisted bilayer systems, in which low-energy flat bands originate solely from the $K/K'$ valleys, in A-AB and A-ABA twisted MoTe$_2$ (\tmt) the moiré bands at low energies arise from both the $\Gamma$ and $K/K'$ valleys, with spin Chern numbers $C_s=0$ (for $\Gamma$) and $C_{\uparrow/\downarrow}=\pm1$ (for $K/K'$), respectively. We show that the multi-valley moiré flat bands are governed by interlayer-hybridization effects, and that different stacking configurations and thicknesses tune the relative energy alignment between the $\Gamma$ and $K$ valley moiré flat bands. By constructing valley-resolved continuum models and performing Wannierization for the low-energy moiré bands, we further uncover that the Berry curvature and quantum metric distributions can be effectively tuned by the layer number and stacking configuration. Unlike other moiré systems, where only one kind of valley influenced the low energy physics, the simultaneous appearance of two distinct types of valleys, with different symmetries, establish A-AB and A-ABA \tmt\ as ideal platforms for studying layer-controlled multi-valley physics.
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All authors Ziyue Qi, Hanqi Pi, Yan Zhang, Jiaxuan Liu, Nicolas Regnault, Hongming Weng, B. Andrei Bernevig, Jiabin Yu, Quansheng Wu

Materials Science · Cross-listed from cs.AI

ToPolyAgent: AI Agents for Coarse-Grained Topological Polymer Simulations

Lijie Ding, Jan-Michael Carrillo and Changwoo Do

We introduce ToPolyAgent, a multi-agent AI framework for performing coarse-grained molecular dynamics (MD) simulations of topological polymers through natural language instructions. By integrating large language models (LLMs) with domain-specific computational tools, ToPolyAgent supports both interactive and autonomous simulation workflows across diverse polymer architectures, including linear, ring, brush, and star polymers, as well as dendrimers. The system consists of four LLM-powered agents: a Config Agent for generating initial polymer-solvent configurations, a Simulation Agent for executing LAMMPS-based MD simulations and conformational analyses, a Report Agent for compiling markdown reports, and a Workflow Agent for streamlined autonomous operations. Interactive mode incorporates user feedback loops for iterative refinements, while autonomous mode enables end-to-end task execution from detailed prompts. We demonstrate ToPolyAgent's versatility through case studies involving diverse polymer architectures under varying solvent condition, thermostats, and simulation lengths. Furthermore, we highlight its potential as a research assistant by directing it to investigate the effect of interaction parameters on the linear polymer conformation, and the influence of grafting density on the persistence length of the brush polymer. By coupling natural language interfaces with rigorous simulation tools, ToPolyAgent lowers barriers to complex computational workflows and advances AI-driven materials discovery in polymer science. It lays the foundation for autonomous and extensible multi-agent scientific research ecosystems.
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Materials Science

Metalorganic Chemical Vapor Deposition of AlScN Thin Films and AlScN/AlN/GaN Heterostructures

Vijay Gopal Thirupakuzi Vangipuram, Abdul Mukit, Kaitian Zhang et al. (+2 more)

AlScN thin films were grown via metalorganic chemical vapor deposition (MOCVD), showing controllable incorporation of scandium (Sc) into the AlN lattices. Systematic variation of growth parameters demonstrated an obvious influence on Sc incorporation, with X-ray photoelectron spectroscopy (XPS) analysis indicating Sc composition up to $\sim$13% when (MCp)$_2$ScCl was used as the precursor. AlScN/AlN/GaN heterostructures grown on GaN templates exhibited the formation of a two-dimensional electron gas (2DEG) channel at the AlScN/AlN–GaN interface, confirming their potential use in high electron mobility transistor (HEMT) device technologies. Variation in AlScN/AlN barrier thickness within the heterostructures showed that thicker barriers yield higher sheet charge densities from both Hall and capacitance-voltage (C–V) measurements. With an AlScN/AlN barrier thickness of $\sim$30~nm, a sheet charge density of $5.22\times10^{12}$~cm$^{-2}$ was extracted from C–V. High-resolution scanning transmission electron microscopy (S/TEM) further confirmed Sc incorporation and revealed the wurtzite crystalline structure of the films and heterostructures. These results establish MOCVD growth of AlScN as a promising and compatible material for advancing III-nitride heterostructures in high-performance electronics and potentially ferroelectrics.
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All authors Vijay Gopal Thirupakuzi Vangipuram, Abdul Mukit, Kaitian Zhang, Salva Salmani-Rezaie, Hongping Zhao

Materials Science · Cross-listed from physics.app-ph

Quantification of Electrolyte Degradation in Lithium-ion Batteries with Neutron Imaging Techniques

Yonggang Hu, Yiqing Liao, Lufeng Yang et al. (+14 more)

Non-destructive characterization of lithium-ion batteries provides critical insights for optimizing performance and lifespan while preserving structural integrity. Optimizing electrolyte design in commercial LIBs requires consideration of composition, electrolyte-to-capacity ratio, spatial distribution, and associated degradation pathways. However, existing non-destructive methods for studying electrolyte infiltration, distribution, and degradation in LIBs lack the spatiotemporal resolution required for precise observation and quantification of the electrolyte. In this study, we employ neutron imaging with sufficient spatial resolution ~150 um and large field of view 20x20 cm2 to quantitatively resolve the electrolyte inventory and distribution within LiFePO4/graphite pouch cells under high-temperature accelerated aging. Quantitative standard curves based on neutron transmission attenuation reveal a clear electrolyte dry-out threshold at 3.18 g Ah-1 and the two stages evolutions of EI during cell aging were quantified. By integrating non-destructive electrochemical diagnostics, accelerated graphite material loss and liquid phase Li+ diffusion degradation is observed during pore-drying. Further analysis, including operando cyclic aging, reveals that the neutron transmission below the saturation reference is due to the enrichment of hydrogen nuclei within the solid-electrolyte interphase. Assumed pore-drying does not occur, the SEI signal of the electrodes can be quantitatively decoupled during ageing. Combined analyses with NI, TOF-SIMS, and SEM reveal that high EI cells exhibit uniform SEI growth and reduced degradation, while low EI cells show uneven SEI formation, accelerating capacity loss. This study unveils a dynamic electrolyte infiltration-consumption-dry-out process in LIBs, offering non-destructive and quantitative insights to guide sustainable and durable battery development.
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All authors Yonggang Hu, Yiqing Liao, Lufeng Yang, Ke Zhang, Yufan Peng, Shijun Tang, Shengxiang Wang, Meifang Ding, Jiahao Wu, Jianrong Lin, Jinding Liang, Yimin Wei, Yanting Jin, Zhengliang Gong, Anatoliy Senyshyn, Jie Chen, Yong Yang

Monday 13 October

Materials Science · Cross-listed from cond-mat.mes-hall

Spontaneous Breaking of the SU(3) Flavor Symmetry in a Quantum Hall Valley Nematic

G. Krizman, A. Kazakov, C.-W. Cho et al. (+10 more)

Two-dimensional quantum materials can host original electronic phases that arise from the interplay of electronic correlations, symmetry and topology. In particular, the spontaneous breaking of internal symmetry that acts simultaneously on the pseudospin and the spatial degree of freedom realizes a nematic ordering. We report evidence of a quantum Hall valley nematic phase with an underlying SU(3) order parameter space obtained by a spontaneous polarization between the threefold degenerate valley pseudospins in Pb1-xSnxSe quantum wells. In the presence of a Zeeman field, we demonstrate a further control of the nematic ordering with an explicit symmetry breaking. Evidence of both spontaneous and explicit SU(3) symmetry breaking, reminiscent of the quark flavor paradigm, is of fundamental interest to shape the many body physics in a SU(3) system.
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All authors G. Krizman, A. Kazakov, C.-W. Cho, V. V. Volobuev, A. Majou, E. Ben Achour, T. Wojtowicz, G. Bauer, Y. Guldner, B. A. Piot, Th. Jolicoeur, G. Springholz, L.-A. de Vaulchier

Materials Science

The Comparison of Colloidal PbS QD Photoconductors and Hybrid Phototransistors

Gökhan Kara, Lorenzo J. A. Ferraresi, Dmitry N. Dirin et al. (+4 more)

The simplicity in the fabrication of photoconductors makes them a valuable choice to investigate optoelectronic properties of colloidal quantum dot (cQD) films. Lateral photoconductors generally require a large size, in the mm2, and are limited in operation speed due to the presence of trapping sites. In contrast, hybrid phototransistors are fabricated in the um2 scale and benefit from such trapping sites, allowing the measurement of low light levels in the nW/cm2. The question, however, arises whether high responsivity values are required for the detection of low light levels or the compatible detectivity of photoconductors is sufficient. Here, we directly compare photoconductors and hybrid phototransistors with an identical EDT-treated PbS cQD film. We highlight that a comparable D* is not enough for the purpose of measuring low light levels, as the resulting photocurrents need to be readily accessible. Furthermore, we also showcase temperature-activated photocurrent dynamics resulting in a negative photocurrent (NPC) effect. This NPC simultaneously improves the frequency bandwidth and photocurrent, enabling operation speeds up to 100 kHz.
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All authors Gökhan Kara, Lorenzo J. A. Ferraresi, Dmitry N. Dirin, Roman Furrer, Maksym V. Kovalenko, Michel Calame, Ivan Shorubalko

Materials Science

Microscopic Intricacies of Self-Healing in Halide Perovskite-Charge Transport Layer Heterostructures

Tejmani Behera, Boris Louis, Lukas Paesen et al. (+7 more)

The stability and performance of halide perovskite photovoltaic devices are critically limited by progressive defect generation and associated local non-radiative losses during operation. Self-healing of defects provides a promising pathway to prolong device functionality, yet the underlying microscopic mechanisms remain poorly understood, particularly the role of interfacial chemistry on trap dynamics and healing kinetics. Here, we elucidate self-healing and defect evolution in triple-cation mixed halide (TCMH) perovskite films and their device-relevant charge transport layer heterostructures subjected to photo-induced damage. Using correlation clustering imaging (CLIM), our recently developed local functional imaging tool, we map spatiotemporal photoluminescence heterogeneity to track defect dynamics in pristine and heterostructure films. The defect healing follows bi-phasic kinetics, with an initial electronic relaxation (tens of minutes) and a subsequent slower phase (~ hours) associated to ionic and lattice rearrangement. Most importantly, our results demonstrate that the chemical nature of charge-transport layers modulates trap activity, healing kinetics, and halide redistribution, with heterostructures exhibiting faster recovery than pristine films, a boon for device resilience. These findings provide new insights into the dynamic interaction between defects, interfaces, and ion migration, and establish a framework for rational design of durable, next-generation perovskite optoelectronic devices.
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All authors Tejmani Behera, Boris Louis, Lukas Paesen, Roel Vanden Brande, Koki Asano, Martin Vacha, Maarten Roeffaers, Elke Debroye, Johan Hofkens, Sudipta Setha

Materials Science

Orbitally-Resolved Mechanical Properties of Solids from Maximally Localized Wannier Functions

Ethan T. Ritz, Guru Khalsa, Hsin-Yu Ko et al. (+3 more)

We present a technique for partitioning the total energy from a semi-local density functional theory calculation into contributions from individual electronic states in a localized Wannier basis. We use our technique to reveal the key role played by the $s$ and $p$ orbitals of the apical oxygen atoms in a curious elastic anomaly exhibited by ferroelectric PbTiO$_3$ under applied stress, which has so far gone unexplained. Our technique enables new insights into the chemical origins of the mechanical properties of materials, or any property given by an energy derivative.
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All authors Ethan T. Ritz, Guru Khalsa, Hsin-Yu Ko, Ju-an Zhang, Robert A. DiStasio Jr., Nicole A. Benedek

Materials Science

Thermal transport in GaN/AlN HEMTs on 4H-SiC: Role of layer thickness and hetero-interfaces

Dat Q. Tran, Minho Kim, Okhyun Nam et al. (+2 more)

Thermal transport in high-electron-mobility-transistor (HEMT) structures grown on 4H-SiC substrates by metalorganic-vapour-phase epitaxy (MOCVD) is systematically investigated. The thermal conductivity of the GaN channel and AlN buffer layers is measured by thermoreflectance (TTR). A pronounced thickness dependence of thermal conductivity as a result of phonon-boundary scattering is observed at low temperatures, while this effect becomes significantly weaker at elevated temperatures. The thermal boundary resistance (TBR) at the AlN/4H-SiC and GaN/AlN interfaces is also examined, showing a substantial reduction and eventual saturation with increasing temperature, indicating elastic phonon transport as the dominant mechanism. Reliable simulations of the temperature profile across the structures based on the measured thermal metrics highlight the critical role of TBR in thin-channel device and the advantage of thicker channel and buffer layers for efficient heat dissipation in the HEMTs.
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All authors Dat Q. Tran, Minho Kim, Okhyun Nam, Vanya Darakchieva, Plamen P. Paskov

Materials Science

Spectroscopy of Sm$^{3+}$ Ions in the C$_{\rm s}$ Symmetry Centres of Hydrothermally Prepared K$_2$YF$_5$ Microcrystals

Pakwan Chanprakhon, Michael F. Reid and and Jon-Paul R. Wells

We report on the synthesis and spectroscopic characterization of Sm$^{3+}$-doped K$_2$YF$_5$ microparticles. The particles were synthesized via the hydrothermal technique, yielding a particle size of approximately 20 $\mu$m in length. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses confirmed their orthorhombic crystal structure. A combination of absorption and laser excited fluorescence performed on samples cooled to 10~K, allow for the determination of {56} experimental crystal-field levels. A parametrised crystal-field analysis for Sm$^{3+}$ in the C$_{\rm s}$ point group symmetry centres of K$_2$YF$_5$ yields good approximation to the data.
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Materials Science

Bond-resolved STM with density-based methods

Emiliano Ventura-Macias, Jose Martinez-Castro, Guillermo Haas et al. (+7 more)

Bond-resolved STM (BRSTM) is a recent technique that combines the advantages of scanning tunneling microscopy (STM) with the outstanding intramolecular resolution provided by non-contact atomic force microscopy (ncAFM) using a CO-functionalized tips, offering unique insights into molecular interactions at surfaces. In this work, we present a novel and easily implementable approach for simulating BRSTM images, which we have applied to reproduce new experimental BRSTM data of Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) on Ag(111), obtained with unprecedented control of tip-sample separation ($\sim$10~pm). Our method integrates the Full-Density-Based Model (FDBM) developed for High-Resolution Atomic Force Microscopy (HRAFM) with Chen's derivative approximation for tunneling channels, effectively capturing the contributions of both $\sigma$ and $\pi$ channels, while accounting for the CO-tip deflection induced by probe-sample interactions. This approach accurately reproduces the experimental results for both PTCDA/Ag(111) and 1,5,9-trioxo-13-azatriangulene (TOAT)/Cu(111) systems, including intricate tip-sample distance-dependent features. Furthermore, we also demonstrate the important role of substrate-induced effects, which can modify molecular orbital occupation and the relaxation of the CO probe, resulting in distinct BRSTM image characteristics.
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All authors Emiliano Ventura-Macias, Jose Martinez-Castro, Guillermo Haas, Jara Trujillo-Mulero, Pablo Pou, Taner Esat, Markus Ternes, Ruslan Temirov, F. Stefan Tautz, Ruben Perez

Materials Science · Cross-listed from physics.chem-ph

Enhancing Diffusion-Based Sampling with Molecular Collective Variables

Juno Nam, Bálint Máté, Artur P. Toshev et al. (+6 more)

Diffusion-based samplers learn to sample complex, high-dimensional distributions using energies or log densities alone, without training data. Yet, they remain impractical for molecular sampling because they are often slower than molecular dynamics and miss thermodynamically relevant modes. Inspired by enhanced sampling, we encourage exploration by introducing a sequential bias along bespoke, information-rich, low-dimensional projections of atomic coordinates known as collective variables (CVs). We introduce a repulsive potential centered on the CVs from recent samples, which pushes future samples towards novel CV regions and effectively increases the temperature in the projected space. Our resulting method improves efficiency, mode discovery, enables the estimation of free energy differences, and retains independent sampling from the approximate Boltzmann distribution via reweighting by the bias. On standard peptide conformational sampling benchmarks, the method recovers diverse conformational states and accurate free energy profiles. We are the first to demonstrate reactive sampling using a diffusion-based sampler, capturing bond breaking and formation with universal interatomic potentials at near-first-principles accuracy. The approach resolves reactive energy landscapes at a fraction of the wall-clock time of standard sampling methods, advancing diffusion-based sampling towards practical use in molecular sciences.
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All authors Juno Nam, Bálint Máté, Artur P. Toshev, Manasa Kaniselvan, Rafael Gómez-Bombarelli, Ricky T. Q. Chen, Brandon Wood, Guan-Horng Liu, Benjamin Kurt Miller

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

Low-field all-optical detection of superconductivity using NV nanodiamonds

Omkar Dhungel, Saravanan Sengottuvel, Mariusz Mrozek et al. (+5 more)

Nitrogen-vacancy centers in nanodiamond offer a microwave-free, noninvasive platform for probing superconductors via near zero-field cross-relaxation magnetometry. We demonstrate this by depositing nanodiamonds on YBCO thin films to measure critical parameters: transition temperature and penetration field. This method leverages nanodiamond fluorescence modulation as a result of magnetic field variation with 1mT amplitude to observe the Meissner effect and field scans to measure the penetration field. The approach is minimally invasive and can be applied to superconducting samples with rough surfaces, facilitating the study of flux vortices and critical phenomena in complex geometries.
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All authors Omkar Dhungel, Saravanan Sengottuvel, Mariusz Mrozek, Till Lenz, Nir Bar-Gill, Adam M. Wojciechowski, Arne Wickenbrock, Dmitry Budker

Materials Science · Cross-listed from physics.class-ph

Advanced creep modelling for polymers: A variable-order fractional calculus approach

José Geraldo Telles Ribeiro and Americo Cunha Jr

Polymer-based plastics exhibit time-dependent deformation under constant stress, known as creep, which can lead to rupture or static fatigue. A common misconception is that materials under tolerable static loads remain unaffected over time. Accurate long-term deformation predictions require experimental creep data, but conventional models based on simple rheological elements like springs and dampers often fall short, lacking the flexibility to capture the power-law behaviour intrinsic to creep processes. The springpot, a fractional calculus-based element, has been used to provide a power-law relationship; however, its fixed-order nature limits its accuracy, particularly when the deformation rate evolves over time. This article introduces a variable-order (VO) springpot model that dynamically adapts to the evolving viscoelastic properties of polymeric materials during creep, capturing changes between glassy, transition and rubbery phases. Model parameters are calibrated using a robust procedure for model identification based on the cross-entropy (CE) method, resulting in physically consistent and accurate predictions. This advanced modelling framework not only overcomes the limitations of the fixed-order models but also establishes a foundation for applying VO mechanics to other viscoelastic materials, providing a valuable tool for predicting long-term material performance in structural applications.
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Materials Science

Epitaxial Electrodeposition of Fe with Controlled In-Plane Variants for Reversible Metal Anode in Aqueous Electrolyte

Chenxi Sui, Ching-Tai Fu, Guangxia Feng et al. (+6 more)

The development of reversible metal anodes is a key challenge for advancing aqueous battery technologies, particularly for scalable and safe stationary energy storage applications. Here we demonstrate a strategy to realize epitaxial electrodeposition of iron (Fe) on single-crystal copper (Cu) substrates in aqueous electrolytes. We compare the electrodeposition behavior of Fe on polycrystalline and single-crystalline Cu substrates, revealing that the latter enables highly uniform, dense, and crystallographically aligned Fe growth. Comprehensive electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analysis confirms the formation of Fe with specific out-of-plane and in-plane orientations, including well-defined rotational variants. Our findings highlight that epitaxial electrodeposition of Fe can suppress dendritic growth and significantly enhance Coulombic efficiency during plating/stripping cycles. This approach bridges fundamental crystallography with practical electrochemical performance, providing a pathway toward high-efficiency aqueous batteries utilizing Earth-abundant materials.
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All authors Chenxi Sui, Ching-Tai Fu, Guangxia Feng, Yuqi Li, Junyan Li, Gangbin Yan, Po-Chun Hsu, Steven Chu, Yi Cui

Materials Science

Strain-induced multiferroicity in Cr1/3NbS2

Y. Sun, Y. Ahn, D. Sapkota et al. (+7 more)

Multiferroic materials, in which electric polarization and magnetic order coexist and couple, offer rich opportunities for both fundamental discovery and technology. However, multiferroicity remains rare due to conflicting electronic requirements for ferroelectricity and magnetism. One route to circumvent this challenge is to exploit the noncollinear ordering of spin cycloids, whose symmetry permits the emergence of polar order. In this work, we introduce another pathway to multiferroic order in which strain generates polarization in materials that host nonpolar spin spirals. To demonstrate this phenomenon, we chose the spin spiral in the well-studied helimagnet Cr1/3NbS2. To detect the induced polarization, we introduce the technique of magnetoelectric birefringence (MEB), an optical probe that enables spatially-resolved and unambiguous detection of polar order. By combining MEB imaging with strain engineering, we confirm the onset of a polar vector at the magnetic transition, establishing strained Cr1/3NbS2 as a type-II multiferroic.
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All authors Y. Sun, Y. Ahn, D. Sapkota, H. S. Arachchige, R. Xue, S. Mozaffari, D. G. Mandrus, L. Zhao, J. Orenstein, V. Sunko

Materials Science

Deterministic hBN bubbles as a versatile platform for studies on single-photon emitters

Piotr Tatarczak, Tomasz Fąs, Jan Pawłowski et al. (+5 more)

Single-photon emitters (SPEs) in two-dimensional materials are highly promising candidates for quantum technologies. SPEs in hexagonal boron nitride (hBN) have been widely investigated, but mostly in exfoliated or powder samples that require an activation process, making it difficult to compare studies and reproduce results. Here, we address this problem and propose a platform based on large-area metaloraganic vapour phase epitaxy (MOVPE)-grown hBN, which combines reproducibility and scalability with the ability to readily host SPEs without activation. Through the creation of bubbles via electron-beam irradiation, we achieve additional functionalities, including an interference-mediated enhancement of emission by approximately 100-200%, dedicated structures that allow the relocation of individual emitters across different systems, and the opportunity to investigate strain-induced effects. Moreover, in contrast to other gas-filled bubbles that deflate at low temperatures, our bubbles remain stable under cryogenic conditions, allowing studies as a function of temperature. To improve the control over the shape and position of bubbles, we demonstrate a~mask-based method that enables deterministic control over bubble formation. The presented hBN bubbles constitute a versatile platform for reproducible studies of hBN-based emitters, providing a reliable insight into their nature and properties.
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All authors Piotr Tatarczak, Tomasz Fąs, Jan Pawłowski, Aleksandra Krystyna Dąbrowska, Jan Suffczyński, Piotr Wróbel, Andrzej Wysmołek, Johannes Binder

Materials Science

Ab-initio calculation of magnetic exchange interactions using the spin-spiral method in VASP: Self-consistent versus magnetic force theorem approaches

Umit Dogan Daglum, Maria Stamenova, Ersoy Sasioglu et al. (+1 more)

We present an ab initio investigation of magnetic exchange interactions using the spin-spiral method implemented in the VASP code, with a comparative analysis of the self-consistent (SC) and magnetic force theorem (MFT) approaches. Using representative 3d ferromagnets (Fe, Co, Ni) and Mn-based full Heusler compounds, we compute magnon dispersion relations directly from spin-spiral total energies and extract real-space Heisenberg exchange parameters via Fourier transformation. Curie temperatures are subsequently estimated within both the mean-field and random-phase approximations. The SC spin-spiral calculations yield exchange parameters and magnon spectra in excellent agreement with previous theoretical data, confirming their quantitative reliability across different classes of magnetic systems. In contrast, the MFT approach exhibits systematic quantitative deviations: it overestimates spin-spiral energies and exchange couplings in high-moment systems such as bcc Fe and the Mn-based Heuslers, while underestimating them in low-moment fcc Ni. The magnitude of these discrepancies increases strongly with magnetic moment size, exceeding several hundred percent in the high-moment compounds. These findings underscore the decisive role of self-consistency in accurately determining magnetic exchange parameters and provide practical guidance for future first-principles studies of spin interactions and excitations using the spin-spiral technique.
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All authors Umit Dogan Daglum, Maria Stamenova, Ersoy Sasioglu, Stefano Sanvito

Materials Science · Cross-listed from physics.comp-ph

Optimal parallelisation strategies for flat histogram Monte Carlo sampling

Hubert J. Naguszewski, Christopher D. Woodgate and David Quigley

Flat histogram methods, such as Wang–Landau sampling, provide a means for high-throughput calculation of phase diagrams of atomistic/lattice model systems. Many parallelisation schemes with varying degrees of complexity have been proposed to accelerate such sampling simulations. In this study, several widely used schemes are benchmarked – both in isolation and in combination – to establish best practice. The schemes studied include energy domain decomposition with both static sizing of energy sub-domains, as well as a dynamic sub-domain sizing scheme which we propose. We also assess the benefits both of replica exchange and of including multiple random walkers per sub-domain, to determine which factors have the largest impact on parallel efficiency. Additionally, the influence of energy sub-domain overlap regions is discussed. As illustrative test cases, we implement and apply the aforementioned strategies to a lattice-based model describing the internal energy of a substitutional alloy, studying the AlTiCrMo refractory high-entropy superalloy as well as the binary CuZn system, both of which crystallographically order into a B2 (CsCl) structure with decreasing temperature. We find that – while all of the proposed strategies confer a non-negligible speedup – parallelisation across energy domains which are non-uniform in size offers the most appreciable performance improvements. This work offers concrete recommendations for which parallelisation strategies should be prioritised to optimally accelerate flat-histogram Monte Carlo simulations.
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Materials Science · Cross-listed from physics.app-ph

Unlocking High-Throughput Heterojunction Discovery

Thomas W. Gries, Davide Regaldo, Yanyan Duan et al. (+8 more)

Photoluminescence (PL) is a ubiquitous proxy for material quality in optoelectronic devices, widely used for high-throughput materials discovery. However, we demonstrate that in the presence of charge-selective contacts, PL loses its predictive reliability and can exhibit strong quenching even in highly efficient photovoltaic devices under open-circuit conditions. By combining steady-state and transient PL with contactless transient surface photovoltage measurements we disentangle the intertwined processes of extraction and recombination, clarifying the physical origin of this phenomenon. This joint approach reveals extraction dynamics not captured by PL alone. A digital replica of the interface shows that Coulomb attraction and interfacial recombination are the fundamental mechanisms driving quenching after charge extraction. Based on these insights, we present a decision tree for heterojunction classification and PL interpretation applicable across diverse optoelectronic systems, including photovoltaics, photodetectors, and LEDs. Our approach supports systematic screening and optimization of half-devices, bridging the gap between accelerated materials discovery and accelerated device discovery.
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All authors Thomas W. Gries, Davide Regaldo, Yanyan Duan, Florian Scheler, Maxim Simmonds, Valerio Stacchini, Annamaria Petrozza, Eva Unger, Antonio Abate, Jean-Paul Kleider, Artem Musiienko

Materials Science

Effects of strain on the stability of the metallic rutile and insulating M1 phases of vanadium dioxide

Peter Mlkvik, Lena Geistlich, Nicola A. Spaldin et al. (+1 more)

We present a systematic density-functional theory study of the effects of strain on the structural and electronic properties in vanadium dioxide (VO$_2$), with particular emphasis on its effect on the relative stability of the metallic rutile and the insulating monoclinic M1 phases. We consider various strain conditions that can be related to epitaxial strain present in VO$_2$ films grown on different lattice planes. Our calculations confirm the dominant role of $c$ axis strain, i.e., along the direction of the V-V dimerization in the M1 phase. Our analysis suggests that this effect stems primarily from the weakening of the lattice stiffness, with the hopping along the $c$ axis playing a minor role. We also confirm that, in strain scenarios that deform the basal plane, the $c$ axis strain still has a dominant effect on the phase stability.
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All authors Peter Mlkvik, Lena Geistlich, Nicola A. Spaldin, Claude Ederer

Materials Science

Enhancing the Plasmonic Hotspot Density via Structural Engineering of Multi-layered MoO3-Ag-Au Systems Under Extreme Electronic Excitation Conditions for Ultra-Sensitive SERS Applications

Om Prakash, Sharmistha Dey, Mayur Khan et al. (+4 more)

We illustrate ion-beam engineering of MoO3 Ag Au multilayer plasmonic substrates to improve SERS performance, We illustrate ion-beam engineering of MoO3-Ag-Au multilayer plasmonic substrates to improve SERS performance. Orthorhombic {\alpha}-MoO3 microflakes were produced via chemical vapour deposition (CVD) on Si-SiO2 substrates. Thin films of Ag (5 nm) and Au (5 nm) were thermally evaporated onto the MoO3 flakes, and the samples were subjected to 100 MeV Ag8+ swift heavy ion irradiation at fluences of 3e11 and 3e12 ions cm-2. Irradiation causes dewetting of metal films, prompting structural and morphological changes that result in the formation of dispersed Ag-Au nanoparticles, enhanced surface roughness, and defect generation within the MoO3 lattice. X-ray diffraction (XRD) verifies the {\alpha}-MoO3 phase; field emission scanning electron microscopy (FESEM) elucidates nanoparticle formation and surface reorganisation; Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) disclose vibrational alterations and binding-energy shifts in Mo 3d, indicative of oxygen vacancies (V_O) and partial reduction of Mo. SERS measurements of molecular probes demonstrate significantly increased Raman intensities following ion irradiation.
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All authors Om Prakash, Sharmistha Dey, Mayur Khan, Abhijith T, Udai Bhan Singh, Ambuj Tripathi, Santanu Ghosh

Materials Science

Host-atom-driven transformation of a honeycomb oxide into a dodecagonal quasicrystal

Martin Haller, Julia Hewelt, V. Y. M. Rajesh Chirala et al. (+5 more)

Dodecagonal oxide quasicrystals (OQCs) have so far been limited to a few elemental systems, with no general formation mechanism established. Here, we demonstrate a versatile approach to OQC formation via a host-atom-induced transformation of a metal-oxide honeycomb (HC) network. Adsorption of Ba, Sr, or Eu onto the HC layer triggers its reorganization into a dodecagonal tiling, as revealed by low-energy electron diffraction and scanning tunneling microscopy. Full conversion occurs when 73% of the honeycomb rings are occupied. Kelvin probe and UV photoelectron spectroscopy show a linear decrease in work function with increasing host coverage, followed by a sharp increase upon quasicrystal formation due to reduced host dipoles. This transformation mechanism enables the fabrication of structurally precise OQCs, including a new Eu-Ti-O phase that extends the field to lanthanide quasicrystals, forming a 2D grid of localized magnetic moments. The method offers a general route to explore lattice-matched substrates for epitaxial growth and may be adapted to other 2D honeycomb materials - such as graphene, hexagonal ice, and silica - paving the way for engineered aperiodic systems beyond transition metal oxides.
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All authors Martin Haller, Julia Hewelt, V. Y. M. Rajesh Chirala, Loi Vinh Tran, Ankur Bhide, Muriel Wegner, Stefan Förster, Wolf Widdra

Materials Science · Cross-listed from cond-mat.mes-hall

Deterministic Switching in Altermagnets via Asymmetric Sublattice Spin Current

Sayan Sarkar, Sunit Das and Amit Agarwal

We demonstrate a deterministic switching mechanism in collinear altermagnets driven by asymmetric sublattice spin currents. Unlike conventional antiferromagnets, where combined parity-time-reversal symmetry enforces purely staggered sublattice spin torques, altermagnets host symmetry-protected nonrelativistic spin splitting that produces unequal torques on the two sublattices. Using doped FeSb$_2$ as a representative $d$-wave altermagnet, our Landau–Lifshitz–Gilbert simulations show that these torques enable magnetic-field-free and deterministic 180$^\circ$ Néel vector reversal over picosecond timescale. The mechanism is generic to even-parity altermagnets and remains effective even in centrosymmetric, weak spin-orbit coupled systems, where the Néel spin-orbit torque mechanism fails. Our results establish an experimentally accessible mechanism for switching of altermagnetic order, opening pathways for realizing ultrafast, low-power altermagnet spintronic devices.
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Materials Science

Electron-phonon coupling in magnetic materials using the local spin density approximation

Á. A. Carrasco Álvarez, M. Giantomassi, J. Lihm et al. (+4 more)

Magnetic materials are crucial for manipulating electron spin and magnetic fields, enabling applications in data storage, spintronics, charge transport, and energy conversion, while also providing insight into fundamental quantum phenomena. In numerous applications, the interaction between electrons and lattice vibrations, known as electron-phonon coupling, can be of significant importance. In that regard, we extend the EPW package to be able to interpolate the electron-phonon matrix elements combining perturbation theory and maximally localized Wannier functions. This allows to use dense momentum grids at a reasonable computational cost when computing electron-phonon-related quantities and physical properties. We validate our implementation considering ferromagnetic iron and nickel, where we explore the phonon induced mass enhancement and Eliashberg spectral function finding different importance of each spin channel for both compounds. Furthermore, we evaluate the carrier resistivity at finite temperatures for both systems, considering the role of the magnetic phase in carrier transport. Our findings indicate that in the case of Fe, the primary contributor to resistivity is electron-phonon scattering. In contrast, for Ni, electron-phonon scattering constitutes less than one-third of the resistivity, underscoring a fundamental difference in the transport properties of the two systems.
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All authors Á. A. Carrasco Álvarez, M. Giantomassi, J. Lihm, G. E. Allemand, M. Mignolet, M. Verstraete, S. Poncé

Materials Science · Cross-listed from quant-ph

Bright Single-Photon Emission from Individual Tin-Vacancy Centers in Multi-Cone Diamond Waveguides

Pablo Tieben, Jan Rhensius, Takuya F. Segawa et al. (+5 more)

Diamonds containing color centers have recently gathered significant attention for photonic quantum technologies, including quantum sensing, photonic quantum computers, and quantum networks. Among the various color centers, tin-vacancy (SnV) centers are particularly promising due to the high emission efficiency from the zero-phonon line and due to their long spin coherence times. However, the extraction of photons from diamond remains a key challenge. Here we demonstrate high photon extraction from a single SnV center incorporated in a diamond nanopillar with tapered sidewalls and a multi-cone structure. A sharp emission peak with a full width at half maximum (FWHM) of $6\,$nm was observed at a wavelength of $619\,$nm. Furthermore, the second-order correlation function exhibited an antibunching dip well below $g^{(2)}(0) = 0.5$, indicating single-photon emission. Remarkably, the emitter achieved a high saturation count rate of approximately $9\,$Mcps. These results establish our nanopillar platform as a promising candidate for bright and stable quantum sources and sensors based on SnV centers in diamond.
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All authors Pablo Tieben, Jan Rhensius, Takuya F. Segawa, Risei Abe, Konosuke Shimazaki, Shigeki Takeuchi, Andeas W. Schell, Hideaki Takashima

Materials Science · Cross-listed from cs.CV

A Large-Language-Model Assisted Automated Scale Bar Detection and Extraction Framework for Scanning Electron Microscopic Images

Yuxuan Chen, Ruotong Yang, Zhengyang Zhang et al. (+2 more)

Microscopic characterizations, such as Scanning Electron Microscopy (SEM), are widely used in scientific research for visualizing and analyzing microstructures. Determining the scale bars is an important first step of accurate SEM analysis; however, currently, it mainly relies on manual operations, which is both time-consuming and prone to errors. To address this issue, we propose a multi-modal and automated scale bar detection and extraction framework that provides concurrent object detection, text detection and text recognition with a Large Language Model (LLM) agent. The proposed framework operates in four phases; i) Automatic Dataset Generation (Auto-DG) model to synthesize a diverse dataset of SEM images ensuring robust training and high generalizability of the model, ii) scale bar object detection, iii) information extraction using a hybrid Optical Character Recognition (OCR) system with DenseNet and Convolutional Recurrent Neural Network (CRNN) based algorithms, iv) an LLM agent to analyze and verify accuracy of the results. The proposed model demonstrates a strong performance in object detection and accurate localization with a precision of 100%, recall of 95.8%, and a mean Average Precision (mAP) of 99.2% at IoU=0.5 and 69.1% at IoU=0.5:0.95. The hybrid OCR system achieved 89% precision, 65% recall, and a 75% F1 score on the Auto-DG dataset, significantly outperforming several mainstream standalone engines, highlighting its reliability for scientific image analysis. The LLM is introduced as a reasoning engine as well as an intelligent assistant that suggests follow-up steps and verifies the results. This automated method powered by an LLM agent significantly enhances the efficiency and accuracy of scale bar detection and extraction in SEM images, providing a valuable tool for microscopic analysis and advancing the field of scientific imaging.
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All authors Yuxuan Chen, Ruotong Yang, Zhengyang Zhang, Mehreen Ahmed, Yanming Wang