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Physics Condensed Matter Materials Science

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Thursday 23 October

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

Sub-10 nm Quantification of Spin and Orbital Magnetic Moment Across the Metamagnetic Phase Transition in FeRh Using EMCD

Jan Hajduček, Veronica Leccese, Ján Rusz et al. (+9 more)

Electron magnetic circular dichroism (EMCD) in transmission electron microscopy (TEM) enables element-specific measurement of spin and orbital magnetic moments, analogous to X-ray magnetic circular dichroism (XMCD). While the EMCD technique offers unmatched spatial resolution, its quantitative accuracy remains under scrutiny, particularly in beam-splitter geometries with convergent probes. Here, we systematically evaluate the limits of quantitative EMCD analysis using the first-order magnetostructural transition in the functional phase-change material FeRh as a tunable magnetic reference. Unlike previous EMCD studies primarily focused on elemental ferromagnets such as Fe, we demonstrate its applicability to a correlated material exhibiting coupled structural and magnetic order. We demonstrate that the extracted orbital-to-spin moment ratio ($m_\text{L}/m_\text{S}$) remains consistent with XMCD benchmarks for TEM probes down to approximately 6 nm, thereby establishing the validity range for reliable quantification. For nm-sized probes with higher convergence angles, we observe an enhanced $m_\text{L}/m_\text{S}$, which we attribute to a combination of instrumental factors and sensitivity to nanoscale heterogeneity within the probed volume. Our results confirm that EMCD provides quantitative agreement with macroscale techniques under suitable conditions, while uniquely enabling spatially confined measurements of local magnetic moments in functional magnetic materials, and allowing the study of interfacial, defect-mediated, or phase-separated magnetism that is inaccessible to photon-based methods.
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All authors Jan Hajduček, Veronica Leccese, Ján Rusz, Jon Ander Arregi, Alexey Sapozhnik, Jáchym Štindl, Francesco Barantani, Paolo Cattaneo, Antoine Andrieux, Vojtěch Uhlíř, Fabrizio Carbone, Thomas LaGrange

Materials Science

Predicting the 3D microstructure of SOFC anodes from 2D SEM images using stochastic microstructure modeling and CNNs

Léon F. Schröder, Sabrina Weber, Lukas Fuchs et al. (+2 more)

The 3D microstructure of solid oxide fuel cell anodes significantly influences their electrochemical performance, but conventional methods for acquiring high-resolution microstructural 3D data such as focused ion beam scanning electron microscopy (FIB-SEM) are costly in both time and resources. In contrast, obtaining 2D images, such as from scanning electron microscopy (SEM), is more accessible, though typically providing insufficient information to accurately characterize the 3D microstructure. To address this challenge, we propose a novel approach that predicts the 3D microstructure from 2D SEM images. The presented method utilizes a low-parametric 3D model from stochastic geometry to generate a large number of virtual 3D microstructures and employs a physics-based SEM simulation tool to obtain the corresponding 2D SEM images. By systematically varying the underlying model parameters, a large dataset can be generated to train convolutional neural networks (CNNs). By doing so, we can statistically reconstruct the 3D microstructure from 2D SEM images by drawing realizations from the stochastic 3D model using the predicted model parameters. In addition, we conducted an error analysis on key geometrical descriptors to quantitatively evaluate the accuracy and reliability of this stereological prediction tool.
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All authors Léon F. Schröder, Sabrina Weber, Lukas Fuchs, Volker Schmidt, Benedikt Prifling

Materials Science

Ultralow-Cost magnetocaloric compound for Cryogenic Cooling

Wei Liu, Benjamin Theisel, Yulia Klunnikova et al. (+2 more)

Cost-effective materials are essential for large-scale deployment. The emerging magnetocaloric hydrogen liquefaction technology could transform the liquid hydrogen industry due to its potential in achieving higher efficiency. Most studies of the cryogenic magnetocaloric effect (MCE) have focused on resource-critical rare-earth-based compounds. Here we report on an ionic magnetocaloric compound FeCl$_2$ which is based on ultralow-cost elements, as a candidate working material for hydrogen liquefaction. FeCl$_2$ shows both inverse and conventional MCE. From 0 to 1.5 T, the inverse effect yields a positive magnetic entropy change ($\Delta S_T$) of about 5 J/kg/K near 20 K, then declines toward zero at higher fields. In contrast, the conventional (negative) response strengthens with field. The $\Delta S_T$ reaches 18.6 J/kg/K near 20 K in magnetic fields of 5 T. This value exceeds most light rare-earth-based compounds and approaches that of heavy rare-earth-based compounds. In magnetic fields of 5 T, the adiabatic temperature change reaches about 3.6 K. The large $\Delta S_T$, along with the low cost of the elements in FeCl$_2$, are prerequisites for inexpensive industrial-scale production, giving the prospect of a practical magnetocaloric candidate for hydrogen liquefaction in the 20 $\sim$ 77 K temperature window.
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All authors Wei Liu, Benjamin Theisel, Yulia Klunnikova, Konstantin Skokov, Oliver Gutfleisch

Materials Science

Vacancy diffusion on a brominated Si(100) surface: Critical effect of the dangling bond charge state

T. V. Pavlova and V. M. Shevlyuga

Silicon dangling bonds (DBs) on an adsorbate-covered Si(100) surface can be created in a scanning tunneling microscope (STM) with high precision required for a number of applications. However, vacancies containing DBs can diffuse, disrupting precisely created structures. In this work, we study the diffusion of Br vacancies on a Si(100)-2$\times$1-Br surface in an STM under typical imaging conditions. In agreement with previous work, Br vacancies diffuse at a positive sample bias voltage. Here, we demonstrated that only vacancies containing a positively charged DB hop across the two atoms of a single Si dimer, while vacancies containing neutral and negatively charged DBs do not. Calculations based on the density functional theory confirmed that positively charged Br (and Cl) vacancies have a minimum activation barrier. We propose that diffusion operates by both one-electron and two-electron mechanisms depending on the applied voltage. Our results show that the DB charge has a critical effect on the vacancy diffusion. This effect should be taken into account when imaging surface structures with charged DBs, as well as when studying the diffusion of other atoms and molecules on the Si(100) surface with vacancies in an adsorbate layer.
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Materials Science

PBr3 Adsorption and Dissociation on the Si(100) Surface

Vladimir M. Shevlyuga, Yulia A. Vorontsova and Tatiana V. Pavlova

The adsorption of PBr3 on the Si(100)-2$\times$1 surface was studied by scanning tunneling microscopy (STM) and density functional theory (DFT). The PBr3 molecule completely dissociates on the Si(100) surface at room temperature into P and Br atoms. In most cases, the dissociated molecule was observed in STM on three neighboring Si dimers. DFT calculations confirm that the PBr3 molecule can completely dissociate at room temperature. After annealing the sample to 400$^{\circ}$C, phosphorus is incorporated into silicon, as evidenced by the Si atoms ejected to the surface. These findings are useful for the insertion of individual phosphorus atoms into silicon by PBr3 adsorption through a halogen mask.
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Materials Science

Unlock Anionic Behavior of Calcium Through Pressure Engineering

Yang Lv, Junwei Li, Jianfu Li et al. (+6 more)

An isolated calcium (Ca) atom has empty d-orbitals under ambient conditions. However, s-d band hybridization has been observed in both elemental Ca and compounds by manipulating thermodynamic conditions. Here, we reveal that the Ca 3d-band can even capture electrons from halogen atoms under pressure, exhibiting anionic behaviors in iodides. We predict a CsCl-type monovalent CaI at above 50 GPa by employing first-principles structural searching and successfully identified the phase at 84 GPa using in situ X-ray diffraction. We further reveal that, due to the effect of orbital broadening, unusual charge transfer from the 5p orbitals of I to the 3d orbitals of Ca in CaI, gradually reverses the ionicity of Ca and becomes the anionic ICa at 485 GPa. Multivalent Ca stabilizes a set of metallic iodides with eight- to ten-fold iodine hyper-coordination. Our findings demonstrate that the valence states of Ca can vary from negative to +2, suggesting much greater complexity of Ca chemistry under ultrahigh pressures.
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All authors Yang Lv, Junwei Li, Jianfu Li, Yong Liu, Jianan Yuan, 1 Jiani Lin, Saori Kawaguchi-Imada, Qingyang Hu, Xiaoli Wang

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

ComProScanner: A multi-agent based framework for composition-property structured data extraction from scientific literature

Aritra Roy, Enrico Grisan, John Buckeridge et al. (+1 more)

Since the advent of various pre-trained large language models, extracting structured knowledge from scientific text has experienced a revolutionary change compared with traditional machine learning or natural language processing techniques. Despite these advances, accessible automated tools that allow users to construct, validate, and visualise datasets from scientific literature extraction remain scarce. We therefore developed ComProScanner, an autonomous multi-agent platform that facilitates the extraction, validation, classification, and visualisation of machine-readable chemical compositions and properties, integrated with synthesis data from journal articles for comprehensive database creation. We evaluated our framework using 100 journal articles against 10 different LLMs, including both open-source and proprietary models, to extract highly complex compositions associated with ceramic piezoelectric materials and corresponding piezoelectric strain coefficients (d33), motivated by the lack of a large dataset for such materials. DeepSeek-V3-0324 outperformed all models with a significant overall accuracy of 0.82. This framework provides a simple, user-friendly, readily-usable package for extracting highly complex experimental data buried in the literature to build machine learning or deep learning datasets.
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All authors Aritra Roy, Enrico Grisan, John Buckeridge, Chiara Gattinoni

Materials Science

Highly Rectifying Cubic Copper Iron Sulfides p-n Junction Diode Fabricated by Anodic Oxidation

Yoshimine Kato, Tomoaki Nakamura, Katsuya Komorita et al. (+1 more)

Rectification properties of semiconductor p-n junction diodes are the basic and important characteristics for electronic device evaluation, especially for novel semiconductor materials. Today's semiconductor devices' fabrication and integration processes require multibillion-dollar investments and are desired to be reduced or simplified. Therefore, low-cost and non-toxic base metal materials with simple fabrication methods are desired for the future semiconductor industry. Recently, copper-based sulfides have been studied for semiconductor devices such as thermoelectric, photovoltaic, or water-splitting applications. Here, a highly rectifying p-n diode of a cubic (disordered) phase Cu4Fe5S8 polycrystal with a zincblende-like structure fabricated by a simple/low-cost wet process is shown. It is found that the Cu4Fe5S8 diode shows the highest rectification ratio in the order of 106 with a large forward current density of 15 Acm-2 (@1.5 V forward bias) at room temperature among the other compounds of copper iron sulfide devices. This remarkable and stable diode characteristic obtained by the p-type layer anodically grown on the sintered n-type cubic-Cu4Fe5S8 can bring the industry closer to low-cost semiconductor manufacturing. These results open a platform of novel semiconductor materials such as cubic-Cu4Fe5S8 with further superior crystal growth and conductive characteristics.
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All authors Yoshimine Kato, Tomoaki Nakamura, Katsuya Komorita, Kungen Teii

Materials Science · Cross-listed from physics.flu-dyn

Microfluidic Study of Evaporation-Driven Crystallization of Saline and Ammonia Brines under Hydrogen Flow

Karol M. Dąbrowski, Mohammad Nooraiepour and Mohammad Masoudi

Underground storage of hydrogen and ammonia in geological formations is essential for renewable energy integration, but salt precipitation during gas injection may threaten storage performance. While extensively studied for CO2 systems, precipitation mechanisms in hydrogen-brine and ammonia-brine systems remain poorly understood. This study presents a comprehensive microfluidic investigation of salt crystallization during hydrogen injection into saline and ammonia-containing brines using high-pressure microfluidics. We conducted 81 high-pressure experiments systematically varying brine composition (1-5 mol/kg NaCl), chemical additives (surfactants, alcohols, ammonia), and hydrogen flow rates (200-1300 mL/min). Quantitative image analysis reveals that hydrogen-induced precipitation differs fundamentally from CO2 systems. Hydrogen drives physical precipitation via evaporation and capillary trapping, producing discrete, localized deposits. In contrast, CO2-ammonia systems generate extensive reactive precipitation of ammonium bicarbonate with interconnected crystal networks. Interfacial tension (IFT) controls both residual brine distribution and final crystal coverage: high-IFT fluids form large, interconnected brine pools promoting extensive crystallization, while low-IFT fluids create isolated pools reducing crystal coverage by 50%. Alcohol and surfactant additives suppress precipitation by enhancing brine mobility, whereas ammonia paradoxically increases crystal fractions despite lower IFT. Higher flow rates accelerate crystallization across all compositions, enabling operational mitigation strategies. and demonstrate that gas-specific, rather than CO2-analog, risk assessments are essential for underground hydrogen storage design. The effectiveness of chemical additives offers promising pathways for near-wellbore protection in underground hydrogen storage operations.
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Materials Science · Cross-listed from cond-mat.mes-hall

Coexisting Massive and Massless Dirac Fermions in Moire'-Reconstructed Bilayer Graphene

Mohit Kumar Jat, Kenji Watanabe, Takashi Taniguchi et al. (+1 more)

We report the emergence of massless Dirac fermions in moiré-reconstructed bands of bilayer graphene (BLG) aligned with hexagonal boron nitride (hBN). Magnetotransport measurements reveal that while the primary BLG band retains a parabolic dispersion with a Berry phase of $2\pi$, the moiré-induced secondary bands at $n/n_0 = \pm 4$ host chiral massless quasiparticles with a Berry phase $\pi$ and a Fermi velocity $v_m \approx 3.6 \times 10^5 \mathrm{m s^{-1}}$. This transition from massive to massless carriers arises from topological band reconstruction driven by the hBN moiré potential. Our results demonstrate that moiré engineering in BLG/hBN offers a powerful route to tune band topology and realize coexisting Dirac and massive fermions within a single crystalline platform.
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All authors Mohit Kumar Jat, Kenji Watanabe, Takashi Taniguchi, Aveek Bid

Materials Science

Non-relativistic spin splitting: Features and Functionalities

Sayantika Bhowal and Arnab Bose

Recently, spin splitting of non-relativistic origin in compensated antiferromagnets has drawn growing attention in condensed matter research. Although many materials, now known to exhibit such spin splitting, have been studied for decades, their manifestation along non-high-symmetry momentum directions initially hindered their recognition. In recent years, significant progress has been made in uncovering the symmetry principles that allow non-relativistic spin splitting in the absence of net magnetization, revealing the unconventional physics arising from their coexistence. In this review, we provide a concise overview of non-relativistic spin splitting in compensated antiferromagnets with various spin configurations, including collinear, coplanar, and non-coplanar spin arrangements. We summarize practical identification guidelines, highlight characteristic features in electronic band structures, and discuss the emerging functionalities, with an emphasis on promising directions for future exploration.
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Materials Science

Domain wall induced topological Hall effect in the chiral-lattice ferromagnet Fe$_x$TaS$_2$

Sk Jamaluddin, Warit Nisaiyok, Yu Zhang et al. (+13 more)

Magnetic topology and its associated emergent phenomena are central to realizing intriguing quantum states and spintronics functionalities. Designing spin textures to achieve strong and distinct electrical responses remains a significant challenge. Layered transition metal dichalcogenides offer a versatile platform for tailoring structural and magnetic properties, enabling access to a wide spectrum of topological magnetic states. Here, we report a domain-wall-driven, large, and tunable topological Hall effect (THE) in a non-centrosymmetric intercalated transition metal dichalcogenides series Fe$_x$TaS$_2$. By systematically varying the Fe intercalation level, we exert precise control over the magnetic ground states, allowing manipulation of the topological Hall effect. Real-space magnetic force microscopy (MFM) provides direct evidence of periodic magnetic stripe domain formation, confirming the microscopic origin of the observed topological transport phenomena. Our findings establish a promising way for tuning the topology of domains to generate substantial electromagnetic responses in layered magnetic materials.
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All authors Sk Jamaluddin, Warit Nisaiyok, Yu Zhang, Hari Bhandari, Brian A. Francisco, Peter E. Siegfried, Fehmi Sami Yasin, Tianyi Wang, Abhijeet Nayak, Mohamed El Gazzah, Resham Babu Regmi, June Ho Yeo, Liuyan Zhao, J. F. Mitchell, Yong-Tao Cui, Nirmal J. Ghimire

Materials Science

Good Enough is Better: Feasibility vs. Pareto-Optimality in Alloy Design

Cayden Maguire, Christofer Hardcastle, Trevor Hastings et al. (+2 more)

In alloy design, the search for candidate materials is often framed as an optimization problem, with the goal of identifying Pareto-optimal solutions across multiple objectives. However, Pareto-optimal solutions do not necessarily satisfy all minimum performance thresholds required for practical deployment. An alternative approach is to treat alloy design as a constraint satisfaction problem, in which the goal is to identify any solution that meets all bare minimum requirements across multiple quantities of interest. These approaches have yet to be benchmarked against each other in the context of realistic alloy design problems. In this work, we demonstrate that, in realistic alloy design campaigns involving multiple objectives and constraints, the constraint satisfaction framework yields a higher likelihood of finding viable alloys than optimization-based approaches. Furthermore, constraint-satisfaction approaches find the first viable alloy solutions earlier than optimization. Our results suggest that focusing on feasibility rather than optimality can lead to more actionable outcomes in materials discovery, particularly in highly constrained applications.
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All authors Cayden Maguire, Christofer Hardcastle, Trevor Hastings, Raymundo Arróyave, Brent Vela

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

Circuit-based cavity magnonics in the ultrastrong and deep-strong coupling regimes

Takahiro Chiba, Ryunosuke Suzuki, Takashi Otaki et al. (+1 more)

We theoretically study nonperturbative strong-coupling phenomena in cavity magnonics systems in which the uniform magnetization dynamics (magnons) in a ferromagnet is coupled to the microwave magnetic field (photons) of a single LC resonator. Starting from an effective circuit model that accounts for the magnetization dynamics described by the Landau-Lifshitz-Gilbert equation, we show that a nontrivial frequency shift emerges in the ultrastrong and deep-strong coupling regimes, whose microscopic origin remains elusive within a purely classical framework. The circuit model is further quantized to derive a minimal quantum mechanical model for generic cavity magnonics, which corresponds to a two-mode version of the Hopfield Hamiltonian and explains the mechanism of the frequency shifts found in the classical circuit model. We also formulate the relation between the frequency shift and quantum quantities, such as the ground-state particle number, quantum fluctuations associated with the Heisenberg uncertainty principle, and entanglement entropy, providing a nondestructive means to experimentally access to these quantum resources. By utilizing soft magnons in an anisotropic ferromagnet, we further demonstrate that these quantum quantities diverge at the zeros of the magnon band edges as a function of the external magnetic field. This work paves the way for cavity magnonics beyond the conventional strong coupling regime.
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All authors Takahiro Chiba, Ryunosuke Suzuki, Takashi Otaki, Hiroaki Matsueda

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

Fabrication and Structural Analysis of Trilayers for Tantalum Josephson Junctions with Ta$_2$O$_5$ Barriers

Raahul Potluri, Rohin Tangirala, Jiangteng Liu et al. (+6 more)

Tantalum (Ta) has emerged as a promising low-loss material, enabling record coherence times in superconducting qubits. This enhanced performance is largely attributed to its stable native oxide, which may host fewer two-level system (TLS) defects, which are the key contributors to decoherence in superconducting circuits. Nevertheless, aluminum oxide remains the predominant choice for Josephson junction (JJ) barriers in most qubit architectures. Here, we investigate techniques for forming high-quality oxide layers on $\alpha$-phase tantalum films to develop tantalum-oxide JJ barriers. We explore thermal oxidation in a tube furnace, rapid thermal annealing, and plasma oxidation of both room-temperature and heated Ta films, characterize the resulting structures using X-ray techniques and electron microscopy, and propose a mechanistic picture of the oxidation pathways. We find that plasma oxidation provides the smoothest Ta$_2$O$_5$ layers, is compatible with in situ Ta deposition, and offers thickness control through the annealing temperature, advantageous for JJ fabrication. Lastly, we evaluate methods for growing Ta/TaO$_x$/Ta trilayers. All trilayers showed c-axis-oriented columnar growth of the bottom Ta layer, with sapphire substrates producing larger, better-aligned grains yet higher dislocation densities than silicon. Nucleation of c-axis-oriented $\alpha$-Ta on tantalum-oxide required an Nb seed layer, as direct Ta deposition yielded amorphous Ta. These results demonstrate the feasibility of $\alpha$-Ta/Nb/TaO$_x$/$\alpha$-Ta stacks for JJs with clean interfaces.
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All authors Raahul Potluri, Rohin Tangirala, Jiangteng Liu, Alejandro Barrios, Praveen Kumar, Sage R. Bauers, Peter V. Sushko, David P. Pappas, Serena Eley

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

Correlation between magnetism and lattice dynamics for cubic FeGe under pressure

R.A. Tonacatl-Monez, R. Heid and O. De la Peña-Seaman

This first-principles study investigates the structural, electronic, lattice dynamical properties, and electron-phonon coupling in ferromagnetic cubic B20 FeGe under applied pressure. The implemented spin-scaling exchange-correlation (ssxc) approach allowed to modify the magnetic moment and ferromagnetic phase energetics using a single scaling parameter, thereby yielding an adjustment of the critical pressure ($p_c$) to its experimental value. The ssxc scheme resulted in a subtle energy shift of the electronic bands in the spin-up channel, and reduced the magnetic moment, bringing it closer to the experimentally reported value. Application of the ssxc approach to phonon dispersion and electron-phonon interaction resulted in a slight mitigation of the pronounced softening and large linewidths of the lowest-frequency acoustic branch close to the $R$-point, typically observed with standard DFT calculations. With increasing pressure, phonon anomaly and linewidths diminish significantly and practically disappear at $p_c$ and beyond. This trend parallels the pressure dependence of the magnetic moment. A comparative analysis of the electronic joint density of states with the phonon linewidths revealed that the momentum dependence of linewidths around the $R$-point closely follow the momentum dependence of the electron-phonon matrix elements. This indicates that the correlation between magnetic moment and linewidths under applied pressure originates from the electron-phonon matrix elements, presenting a distinct scenario compared to other B20 family members, where nesting plays a more dominating role.
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Wednesday 22 October

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

Laser Patterning of Superhydrophobic transparent glass surfaces with anti-fogging and anti-icing applications

Laura Montes-Montañez, Fernando Nuñez-Galvez, Melania Sanchez-Villa et al. (+11 more)

This work addresses the fabrication of transparent glass surfaces with superior water-repellence (i.e., superhydrophobicity), and related functional properties such as omniphobicity, anti-fogging and anti-icing responses. Surfaces have been processed by means of mild femtosecond laser patterning combined with the grafting of fluorinated tethered molecules. Controlling the laser scan and ablation conditions permits the fabrication of under-design grooves with cross and lineal morphologies and separations between 10 and 500 um. These patterns provide a high transparency and repellence to liquids and ice over large areas. The best performance is obtained for cross or parallel line patterned glass with microgrooves separated by 100 um and 15 um depth thanks to 5 laser scanning repetitions. These surfaces present a stable Cassie-Baxter wetting state and very low ice-adhesion strength while keeping up to 80 % of optical transmittance in the visible region. Anti-fouling tests, along with freezing and thawing cycles on these surfaces, have demonstrated a remarkable and durable self-cleaning response, even under environmentally stressful conditions. Water condensation experiments conducted under atmospheric conditions, as well as in an environmental electron scanning microscope, have revealed important issues related to the formation of supercooled water droplets. These experiments show that the patterned breakdown of surface properties effectively prevents extensive fogging and water accumulation. This feature is particularly crucial for outdoors and low temperature applications where the preservation of transparency is essential.
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All authors Laura Montes-Montañez, Fernando Nuñez-Galvez, Melania Sanchez-Villa, Luis A. Angurel, Heli Koivuluo-to, German F. de la Fuente, Víctor Trillaud, Philippe Steyer, Karine Masenelli-Varlot, Francisco J. Palomares, Ana Borrás, Agustín R. González-Elipe, Carmen López-Santos, Víctor Rico

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

A Universal Chern Model on Arbitrary Triangulations

Nigel Higson and Emil Prodan

Given a triangulation of a closed orientable surface, we place single-mode resonators or single-orbital artificial atoms at its vertices, edges and facets, and we devise near-neighbor hopping terms derived from the boundary and Poincaré duality maps of the simplicial complex of the triangulation. Regardless of the surface or its triangulation, these terms always lead to tight-binding Hamiltonians with large and clean topological spectral gaps, carrying non-trivial Chern numbers in the limit of infinite refinement of the triangulation. We confirm this via numerical simulations, and demonstrate how these models enable topological edge modes at the surfaces of real-world objects. Furthermore, we describe a metamaterial whose dynamics reproduces that of the proposed model, thus bringing the topological metamaterials closer to real-world applications.
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Materials Science · Cross-listed from cond-mat.soft

Coupled imbibition and evaporation of droplets deposited on a nanoporous layer

Joachim Trosseille, Hugo Bellezza and Olivier Vincent

Liquids in nanoscale hydrophilic pores generate capillary pressures so large that they could theoretically climb kilometers against gravity. However, droplets on thin nanoporous layers form imbibition fronts stopping at millimeters or less due to evaporation competing with capillary flow. Such droplet infiltration dynamics is of growing interest for studying confined fluids and for applications such as water harvesting, printing, chemical delivery, actuation, and sensing. Here, we investigate theoretically and experimentally the spontaneous imbibition and evaporation of sessile droplets into thin mesoporous layers, focusing on their dependence on imposed relative humidity (RH). Theoretically, we provide a unified analytical approach for the dynamics of the wetted annulus ("halo") around the droplet, accounting for arbitrary halo dimensions and confinement-induced thermodynamic shifts (Kelvin effect). Experimentally, we study water droplets on oxidized porous silicon layers (pore diameter 3-4 nm, thickness 5 $\mu$m), systematically investigating how halo and droplet dynamics depend on RH. We show that halo formation timescales diverge at a critical RH due to the Kelvin effect, as illustrated by comparing RH-dependent evaporation rates in the halo (confined liquid) and in the droplet (bulk liquid). Our analysis also reveals an apparent divergence of the imbibition coefficient, unexplained by standard capillary models, suggesting a key role for Kelvin-driven vapor transport along the porous surface. The complex couplings revealed by our study call for caution in interpreting halo dynamics data. Our results also highlight RH as a powerful control parameter for tuning droplet imbibition behavior and infiltration patterns.
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Materials Science

A unified picture of phonon anomalies in crystals and glasses

Alessio Zaccone

Phonon spectra in solids often display anomalies that defy the simple Debye law, most prominently the van Hove singularity in crystals and the boson peak in glasses. Although traditionally regarded as distinct, both features are increasingly recognized as sharing a common physical origin. In a recent work, G. Ding et al. (Nat. Phys. 2025) propose a resonant-damping model that unifies these anomalies within a single framework. By coupling phonon damping to vibrational softening, their theory explains why some materials exhibit van Hove peaks, others boson peaks, and many show both. This advance extends earlier ideas and theories of Baggioli and Zaccone on the competition between phonon propagation and damping, while also connecting to microscopic mechanisms such as nonaffine motions in glasses. The resonant-damping paradigm thus offers a promising step toward a unified understanding of vibrational anomalies across ordered and disordered solids.
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Materials Science

Hexa-Graphyne: A Transparent and Semimetallic 2D Carbon Allotrope with Distinct Optical Properties

Jhionathan de Lima and Cristiano Francisco Woellner

Herein, we conduct a comprehensive investigation of Hexa-graphyne (HXGY), a planar carbon allotrope formed by distorted hexagonal and rectangular rings incorporating sp and sp$^2$-hybridized carbon atoms. First-principles calculations confirm its energetic, dynamical and thermal stability (up to at least 1000 K). Regarding its band structure, this material exhibits a semimetallic nature. It exhibits high mechanical compliance, with a Young's modulus approximately 13 times lower and a Poisson's ratio nearly 4 times higher than those of graphene. The optical response is marked by strong ultraviolet absorption, high infrared reflectivity, and pronounced transparency in the visible-light range. Raman and infrared spectra exhibit sharp and well-separated peaks, providing a clear signature of acetylenic linkage stretching vibrations. Nanoribbon structures derived from HXGY show distinct electronic behaviors depending on the edge termination type and width. These findings highlight the HXGY potential for nanoelectronic and optoelectronic applications.
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Materials Science

Accelerating Moment Tensor Potentials through Post-Training Pruning

Zijian Meng, Karim Zongo, Matthew Thoms et al. (+2 more)

Moment Tensor Potentials (MTPs) are machine-learning interatomic potentials whose basis functions are typically selected using a level-based scheme that is data-agnostic. We introduce a post-training, cost-aware pruning strategy that removes expensive basis functions with minimal loss of accuracy. Applied to nickel and silicon-oxygen systems, it yields models up to seven times faster than standard MTPs. The method requires no new data and remains fully compatible with current MTP implementations.
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All authors Zijian Meng, Karim Zongo, Matthew Thoms, Ryan Eric Grant, Laurent Karim Béland

Materials Science

Unraveling the defect landscape of wide-bandgap perovskites from electrical and photoelectrical characterization of thin films and solar cells

L. Kopprio, J. Caram, S. Le Gall et al. (+7 more)

Understanding and controlling defect states in halide perovskites is critical to advancing their performance in solar cells, yet their complex defect landscape remains elusive. Charged defects in perovskites can migrate under an applied electric field, complicating their characterization by conventional approaches. Here, we integrate current-voltage (IV) and thermal admittance spectroscopy (TAS) with lateral photocurrent methods, including thermal steady-state photocurrent (SSPC) and steady-state photocarrier grating (SSPG), to probe the kinetic and electrical properties of defects in thin films of vacuum-deposited FA$_{0.7}$Cs$_{0.3}$Pb(I$_{0.9}$Br$_{0.1}$)$_3$ perovskite. The experimental results are interpreted with advanced numerical simulations to account not only for the energy positions of defects in the bandgap but also for their mobilities. The low activation energies observed in the capacitance steps rule out free-carrier trapping and emission as their origin, pointing instead to charged-defect (or ionic) migration. We estimate the free-carrier mobilities and the defect distribution inside the bandgap, along with their capture coefficients. Our results reveal exponential bandtail states arising from dynamic lattice disorder and identify a Gaussian-like defect distribution 0.21~eV from the band edge, which dominates recombination. Donors and acceptors are present at nearly equal concentrations ($\sim 2 \times 10^{18}$~cm$^{-3}$). The mobile species responsible for the capacitance steps is one of the dopants, exhibiting an average mobility of $10^{-8}$~cm$^2$~V$^{-1}$~s$^{-1}$ at 300~K with a thermal activation energy of around 0.34~eV.
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All authors L. Kopprio, J. Caram, S. Le Gall, F. Ventosinos, L. Gil-Escrig, H. J. Bolink, J. Alvarez, C. Longeaud, J-P. Kleider, J. Schmidt

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

Spin-Locked Helical Currents and Charge-Neutral Spin-Channel Pumping in Altermagnetic Nanotubes

Xin Chen, Zhen Han, Linyang Li et al. (+1 more)

Altermagnetism has been widely explored in 3D and 2D crystals, but its one-dimensional realization remains largely unexplored. Here we propose an altermagnetic nanotube formed by rolling a 2D altermagnet, which converts \textcolor{black}{symmetry-enforced directional spin anisotropy in momentum space} into \textcolor{black}{spin–chirality locking in the screw-symmetric geometry}. Unlike curvature-induced magnetization in bent films, \textcolor{black}{the nanotube remains compensated and produces no net magnetization}. Two reciprocal effects emerge: (i) \textcolor{black}{spin-selective} injection drives a helical current whose handedness is fixed by the spin, yielding opposite-sign axial magnetic fields; and (ii) a time-varying axial flux generates a circumferential Faraday field that drives \textcolor{black}{equal and opposite axial charge currents in the two fixed spin channels, yielding a charge-neutral spin-channel current in the open-circuit weak-SOC limit}. \textcolor{black}{Explicit the first-principles calculations of the relaxed V$_2$Se$_2$O nanotube reveal spin-resolved helical $|\psi|^2$ modulations near both band edges, while a parent-monolayer Wannier–Boltzmann calculation quantifies the energy-dependent spin-odd transverse response and corresponding ideal thin-wall field scale.
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All authors Xin Chen, Zhen Han, Linyang Li, Mingwen Zhao

Materials Science · Cross-listed from physics.optics

High Uniformity GaN Micro-pyramids and Platelets by Selective Area Growth

Changhao Li, Vitaly Z. Zubialevich, Peter J. Parbrook et al. (+2 more)

The development of uniform GaN micro-pyramids and platelets via selective area growth is a critical step toward advancing III-nitride device technologies, particularly for micro-light-emitting diode applications. This work investigates the origins of morphological non-uniformity in micro-pyramids and micro-platelets grown by metal-organic chemical vapor deposition (MOCVD). We observe that a direct one-step growth approach leads to significant growth rate inhomogeneity across arrays. To shed light on this issue, we examine the mechanisms driving non-uniformity and explore process modifications aimed at mitigating these effects. Building on these insights, we propose a controlled multi-step growth strategy that combines sequen-tial growth and thermal treatment phases. This approach is demonstrated to enhance surface morphology and structural regularity. The work contributes to the broader objective of enabling scalable, high-precision GaN microstructure fabrication for next-generation optoelectronic applications.
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All authors Changhao Li, Vitaly Z. Zubialevich, Peter J. Parbrook, Brian Corbett, Zhi Li

Materials Science

Dara: Automated multiple-hypothesis phase identification and refinement from powder X-ray diffraction

Yuxing Fei, Matthew J. McDermott, Christopher L. Rom et al. (+2 more)

Powder X-ray diffraction (XRD) is a foundational technique for characterizing crystalline materials. However, the reliable interpretation of XRD patterns, particularly in multiphase systems, remains a manual and expertise-demanding task. As a characterization method that only provides structural information, multiple reference phases can often be fit to a single pattern, leading to potential misinterpretation when alternative solutions are overlooked. To ease humans' efforts and address the challenge, we introduce Dara (Data-driven Automated Rietveld Analysis), a framework designed to automate the robust identification and refinement of multiple phases from powder XRD data. Dara performs an exhaustive tree search over all plausible phase combinations within a given chemical space and validates each hypothesis using a robust Rietveld refinement routine (BGMN). Key features include structural database filtering, automatic clustering of isostructural phases during tree expansion, peak-matching-based scoring to identify promising phases for refinement. When ambiguity exists, Dara generates multiple hypothesis which can then be decided between by human experts or with further characteriztion tools. By enhancing the reliability and accuracy of phase identification, Dara enables scalable analysis of realistic complex XRD patterns and provides a foundation for integration into multimodal characterization workflows, moving toward fully self-driving materials discovery.
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All authors Yuxing Fei, Matthew J. McDermott, Christopher L. Rom, Shilong Wang, Gerbrand Ceder

Materials Science

DFT-informed Design of Radiation-Resistant Dilute Ternary Cu Alloys

Vaibhav Vasudevan, Thomas Schuler, Pascal Bellon et al. (+1 more)

This research establishes a systematic, high-throughput computational framework for designing radiation-resistant, dilute ternary copper-based alloys by addition of solutes that bind to vacancies and reduce their mobility, thus promoting interstitial-vacancy recombination. The first challenge in developing alloys by this method is mitigating the vacancy-mediated solute drag effect, since density functional theory (DFT) calculations show that solutes that bind strongly to vacancies are also rapidly dragged to point-defect sinks, and thus removed from the matrix. To overcome this issue, two types of solutes are added to the Cu matrix: A first solute with a strong vacancy binding energy (B-type species) and another solute that binds to 'B' and is a slow diffuser in Cu (C-type species). Using DFT, 21 synergistic solute pairs are screened, with 'B'=Zr, Ge, Sn and 'C'=Fe, Co, Mo, Ni, Nb, W, Cr. Two promising alloys, Cu(Zr,Co) and Cu(Zr,Fe) are then investigated in detail in the dilute regime. Diffusion and solute drag in these alloys are modeled using the kinetic cluster expansion approach (KineCluE) under irradiation conditions. It is shown that strong Zr-'C' thermodynamic binding, especially between Zr and Co, significantly reduces the mobility of Zr solute and suppresses the vacancy-mediated solute drag. Using an analytical framework for the standard five-jump frequency model for diffusion in binary alloys, it is found that vacancy-Zr-Co triplets disrupt the kinetic circuits that promote solute drag in the binary alloy by raising the dissociation barrier for the vacancy from the solute.
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All authors Vaibhav Vasudevan, Thomas Schuler, Pascal Bellon, Robert Averback

Materials Science

Atomic displacements drive flat band formation and lateral electron and hole separation in near-60 degree twisted MoSe2/WSe2 bilayers

Madeleine Phillips and C. Stephen Hellberg

Transition metal dichalcogenide (TMD) bilayers with an interlayer twist exhibit a moire super-period, whose effects can manifest in both structural and electronic properties. Atomic displacements can lead to reconstruction into domains of aligned stacking, and flat bands can form that may host correlated electron states. In heterobilayers angular mismatch is nearly unavoidable, so understanding the consequences of an interlayer twist is essential. Using ab initio density functional theory, we find that in near-60 degree twisted MoSe2/WSe2 bilayers valence and conduction band flat bands emerge at ~3 degree twist. Despite relatively limited reconstruction at these angles, atomic displacement creates a polarization gradient that forms a confining potential, localizing and laterally separating electrons and holes within the moire supercell. Excitons formed from flat band electrons and holes should therefore have not only the out-of-plane dipole moment familiar from MoSe2/WSe2 interlayer excitons, but an in-plane dipole moment as well.
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Materials Science

Intrinsic nonlinear Hall effect beyond Bloch geometry

Raffaele Resta

The theory of the intrinsic Hall effect, both linear and nonlinear, is rooted in a geometry which is defined in the Bloch-vector parameter space; the formal expressions are mostly derived from semiclassical concepts. When disorder and interaction are considered there is no Bloch vector to speak of; one needs a more general quantum geometry, defined in a different parameter space. The nonlinear Hall effect is a fundamental geometric response of the many-body ground state, not a band-structure peculiarity. The higher-level geometrical formulation of the intrinsic Hall effect provides very compact expressions, which have the additional virtue – in the Bloch special case – of yielding the known results in a straightforward way: the logic is not concealed by the algebra.
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Materials Science

Active high-entropy photocatalyst designed by incorporating alkali metals to achieve d0+d10+s0 cationic configurations and wide electronegativity mismatch

Jacqueline Hidalgo-Jimenez, Taner Akbay, Tatsumi Ishihara et al. (+1 more)

Photocatalytic hydrogen (H2) production and carbon dioxide (CO2) conversion to methane (CH4) are considered promising solutions for reducing CO2 emissions. However, the development of highly active photocatalysts is essential to efficiently drive these reactions without harming the environment. In this study, we introduce a strategy that incorporates elements with both low and high electronegativities into catalysts based on transition metals, thereby enhancing both reactant adsorption and charge transfer. This strategy is implemented in a high-entropy oxide (HEO) by adding cesium, an alkali metal with very low electronegativity, and gallium, a metal with high electronegativity, to transition metals titanium, niobium and tantalum. The resulting oxide, TiNbTaGaCsO9 with a large concentration of oxygen vacancies, exhibits strong light absorption, a low bandgap and a suitable band structure for both hydrogen evolution and CO2 conversion. Compared to HEOs with only d0 or d0+d10 cationic configurations, the synthesized oxide with a wide electronegativity difference and mixed d0+d10+s0 cationic configurations shows significantly higher activity for both H2 and CH4 production, even without using a cocatalyst. These results demonstrate a design strategy for creating highly active HEOs containing alkali metals by taking advantage of the electronegativity mismatch across the periodic table.
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All authors Jacqueline Hidalgo-Jimenez, Taner Akbay, Tatsumi Ishihara, Kaveh Edalati