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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Wednesday 8 October

Materials Science

SiC-TGAP: A machine learning interatomic potential for radiation damage simulations in 3C-SiC

Ali Hamedani and Andrea E.Sand

Silicon carbide (SiC) has long been a subject of study for its application in harsh environments. Existing empirical interatomic potentials for 3C-SiC show significant discrepancies in predicting the properties that are crucial in describing the evolution of defects generated in collision cascades. We present a Gaussian approximation potential model for 3C-SiC (TGAP) trained by two-body and the turboSOAP many-body descriptors. The dataset covers crystalline, liquid and amorphous phases. To accurately capture defect dynamics, twenty-one defect types have been included in the dataset. TGAP captures the experimentally observed decomposition of carbon atoms in the liquid phase at atmospheric pressure, while also accurately reproducing the radial distribution function of the high-temperature homogeneous liquid phase across a range of densities. Moreover, it predicts the melting point in very good agreement with density functional theory and experiments. The potential is equipped with the Nordlund-Lehtola-Hobler repulsive potential to capture the high repulsion of recoils in the collision cascades. TGAP provides an accurate tool for atomistic simulation of radiation damage in cubic SiC.
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Materials Science

Microstructure sensitive recurrent neural network surrogate model of crystal plasticity

Michael D. Atkinson, Michael D. White, Adam J. Plowman et al. (+1 more)

The development of next-generation structural materials for harsh environments requires rapid assessment of mechanical performance and its dependence on microstructure. While full-field crystal plasticity (CP) models provide detailed insights, the high computational cost limits their use with uncertainty quantification workflows and in component-scale simulation. Surrogate models based on recurrent neural networks (RNNs) have shown promise in reproducing history-dependent mechanical behaviour but are applied to models with either fixed microstructure or representative volume elements. Here, we develop a microstructure sensitive RNN surrogate that predicts homogenised stress responses directly from three-dimensional grain structures and arbitrary deformation histories. The architecture employs a gated recurrent unit (GRU) with mappings from microstructure to both the initial hidden state and sequence inputs, allowing the model to capture path dependence and microstructure variability. Training data comprised of over 300,000 CP simulations generated using combinations of randomly generated microstructures and loading paths. The model was found to reproduce CP predictions for both in-distribution validation data and unseen deformation modes, with errors of 2 MPa to 3 MPa. Out-of-distribution microstructures were more difficult to predict, emphasising the need for representative training data with, for example, heavily textured microstructures. Embedding the model into a multiscale framework demonstrates its ability to replace conventional constitutive updates, reducing computational cost while preserving key features of the stress distribution. These results establish microstructure-informed RNN surrogates as a promising alternative to direct CP simulations, offering a pathway toward rapid multiscale modelling and uncertainty quantification.
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All authors Michael D. Atkinson, Michael D. White, Adam J. Plowman, Pratheek Shanthraj

Materials Science

Uncovering domain morphology in an unconventional magnet with scanning diamond quantum magnetometry

Freya Johnson, Jan Zemen, Helena Knowles et al. (+1 more)

Unconventional magnetic materials including non-collinear antiferromagnets, p-wave magnets and altermagnets, are an emerging frontier for quantum spintronics and hybrid quantum devices. Critical to the application of these materials is control over the magnetic domain state, as their unique, symmetry-driven properties vanish in a multi-domain limit. However, the mechanisms governing domain formation in materials with compensated local moments remain poorly understood. In this work, we examine the ferrimagnetic to non-collinear antiferromagnetic phase transition of Mn3NiN using scanning nitrogen-vacancy centre magnetometry. We provide nanoscale mapping of the magnetic domain evolution on cooling and correlate the local stray fields with global magnetometry and anomalous Hall effect measurements. We observe the formation of a disordered, dendritic domain structure whose roughness is quantified using its fractal dimension. The fractal dimension steadily increases on cooling through the transition, saturating at a value of ~ 1.55 in the non-collinear phase, but the domain area distribution does not show any significant changes. We show this behaviour cannot be explained by the balance of demagnetisation energy and domain wall energy, and conclude elastic contributions and defects are a critical factor to explain the domain size.
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All authors Freya Johnson, Jan Zemen, Helena Knowles, Lesley F. Cohen

Materials Science

Exploring the Physical Properties, Hydrogen Storage Capacity and Thermal Barrier Performance of LaMg2H7: A First-Principles Investigation

Tanvir Khan, Md Hasan Shahriar Rifat, M. Ibrahim et al. (+3 more)

LaMg2H7 is a ternary wide band gap semiconductor that is a member of the hydride family. The bulk physical characteristics of the LaMg2H7 compound, including its structural, electronic band structure, elastic, thermal, and optical characteristics, have been examined in this work utilizing density functional theory (DFT). The elastic constants indicate that LaMg_2H_7 is mechanically stable, brittle in nature, and anisotropic. This studied compound possesses a moderate level of hardness. The band structure and density of states have been examined to have a better understanding of its electronic behavior. The intrinsic carrier concentrations and effective masses have been determined using the band structure. The gravimetric hydrogen storage capacity (Cwt%) has been calculated, indicating that this compound is suitable for hydrogen storage applications. This compound is dynamically stable, as confirmed by its phonon dispersion. Here, the details of this wide-band-gap semiconductor's reflectivity, absorption coefficient, refractive index, dielectric function, optical conductivity, and loss function are investigated. The substance is a moderate reflector of ultraviolet (UV) light. The absorption and conductivity support the gap in the band structure. The thermodynamic properties, such as bulk modulus, internal energy, specific heat capacity, entropy, thermal expansion coefficient, and Debye temperature, have been explored at varying temperatures and pressures. LaMg_2H_7 has a moderate level of melting temperature with higher lattice thermal conductivity. The value of the thermal expansion coefficient and minimum thermal conductivity is highly recommended for use as a thermal barrier coating (TBC).
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All authors Tanvir Khan, Md Hasan Shahriar Rifat, M. Ibrahim, J.H. Abir, Saptak Roy, S.H. Naqib

Materials Science

Ground state magnetic structure of Mn3Sn

Jeppe Jon Cederholm, Zhian Xu, Yanfeng Guo et al. (+11 more)

We use spherical neutron polarimetry to determine the ground state magnetic structure of Mn3Sn. We find that Mn3Sn adopts an inverse triangular structure with spins parallel to <100> (Type III) rather than spins parallel to <110> (Type IV). Density functional theory calculations reveal no energy difference between these two structures, suggesting that the selection is caused by subtle effects such as sixth-order anisotropy. Partial control of the magnetic domain population through a moderate magnetic field is key to distinguish between the two models. We find that three of the six domains are approximately equally populated, while the others have negligible population. Upon entering the low temperature incommensurate phase, the domain structure is lost. The domains decouple from the magnetic field, and can therefore not be controlled by any known method.
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All authors Jeppe Jon Cederholm, Zhian Xu, Yanfeng Guo, Martin Ovesen, Thomas Olsen, Kristine M. L. Krighaar, Chrystalla Knekna, Jian Rui Soh, Youngro Lee, Navid Qureshi, Jose Alberto Rodriguez Velamazan, Eric Ressouche, Andrew T. Boothroyd, Henrik Jacobsen

Materials Science

Modular Reactor for In Situ X-ray Scattering, Spectroscopy, and ATR-IR Studies of Solvothermal Nanoparticle Synthesis

Sani Y. Harouna-Mayer, Melike Gumus Akcaalan, Jagadesh Kopula Kesavan et al. (+14 more)

Understanding the chemical processes that occur during the solvothermal synthesis of functional nanomaterials is essential for their rational design and optimization for specific applications. However, these processes remain poorly understood, primarily due to the limitations of conventional ex situ characterization techniques and the technical challenges associated with in situ studies, particularly the design and implementation of suitable reactors. Here, we present a versatile cell suitable for in situ X-ray scattering, X-ray spectroscopy, and infrared spectroscopy studies performed during solvothermal synthesis under autoclave-like, inert conditions. The reactor enables precise control of the temperature between -20 C and 200 C, pressures up to 8 bar, magnetic stirring, and injection of gas or liquids. The reactor's capabilities are demonstrated by comprehensively studying the solvothermal synthesis of magnetite nanoparticles from iron acetylacetonate in benzyl alcohol through in situ X-ray scattering and spectroscopy, and ATR-IR spectroscopy.
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All authors Sani Y. Harouna-Mayer, Melike Gumus Akcaalan, Jagadesh Kopula Kesavan, Tjark R. L. Groene, Lars Klemeyer, Sarah-Alexandra Hussak, Lukas Grote, a Davide Derelli, Francesco Caddeo, Cecilia Zito, Paul Stützle, Dorota Speer, Ann-Christin Dippel, Blanka Detlefs, Yannik Appiarius, Axel Jacobi von Wangelin, Dorota Koziej

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

Quasiparticle Description of Angle-Resolved Photoemission Spectroscopy for SrCuO2

Dimitar Pashov, Casey Eichstaedt, Swagata Acharya et al. (+1 more)

SrCuO2 has long been considered a near-archetypal realization of a quasi one dimensional (1D) system of interacting electrons with short-range interactions. Within this framework, experimental observations - interpreted through the lens of the 1D Hubbard model-suggest that electron and hole excitations decay into two types of (unphysical) collective bosonic modes: spinons, which carry the spin degree of freedom, and holons, which carry the charge degree of freedom. This model, known as spin-charge separation, is most directly evidenced by angle-resolved photoemission spectroscopy (ARPES), where a photo-induced hole decays into a continuum of these excitations. Here we present an alternative perspective grounded in first-principles, self-consistent, and parameter-free many-body perturbation theory. In this revised quasiparticle framework, ARPES can be understood as a one-body effect arising from mild disorder in a long-range antiferromagnetic ground state. the emergence of the so-called spinon branch arises naturally from spin disorder, the anomalous line widths are accurately captured, and we provide a compelling explanation for the spectral weight observed at the non-magnetic zone boundary. This reinterpretation provides a unified explanation for key experimental signatures previously attributed to spin-charge separation, including features observed in optical conductivity. Additionally, we show that SrCuO2 exhibits a nontrivial interchain coupling that significantly influences both its one-particle and two-particle spectral functions. By comparing the spectral features of SrCuO2 with those of La2CuO4, we argue that SrCuO2 shares notable similarities with the two-dimensional cuprates - both being rooted in a common CuO4 plaquette-based molecular orbital framework.
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All authors Dimitar Pashov, Casey Eichstaedt, Swagata Acharya, Mark van Schilfgaarde

Materials Science

Phase relation investigation of U-La-O system under oxidizing conditions and observation of novel meta-stable and mixed-valent uranium phase- Ln3U11O36 (Ln=La, Nd, Sm, Gd)

Shafeeq Muhammed, Geeta Patkare and Rohan Phatak

Total of twelve samples in the U-La-O system with the compositions U1-yLayO2+x (y=0.025, 0.05, 0.1, up to 0.3) were synthesized by gel combustion synthesis method followed by appropriate heat treatment in air atmosphere. Comprehensive experimental analysis using various techniques like X-ray diffraction, thermogravimetry and oxygen to uranium ratio (O/U) are used to establish the phase relation in U1-yLayO2+x system at 1173 K and 1523 K heated in air. A novel meta-stable phase with stoichiometry La3U11O36 having mixed-valent uranium is reported for the first time in U-La-O system. The thermal property of this new phase is reported along with the updated phase relations at and above 1173 K temperature for the compositions U1-yLayO2+x (y < 0.3). Further, formation and stability of this new Ln3U11O36 phase was also investigated with smaller cations like Nd3+, Sm3+, Gd3+ and the smallest Y3+ cation.
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Materials Science · Cross-listed from cond-mat.mes-hall

Intrinsic ultrafast edge photocurrent dynamics in WTe$_2$ driven by broken crystal symmetry

Subhashri Chatterjee, Katsumasa Yoshioka, Taro Wakamura et al. (+2 more)

Directional photocurrents in two-dimensional materials arise from broken crystal symmetry, offering pathways to high-speed, bias-free photodetection beyond conventional devices. Tungsten ditelluride (WTe$_2$), a type-II Weyl semimetal, exhibits robust symmetry-breaking-induced edge photocurrents from competing nonlinear optical and photothermoelectric mechanisms, whose intrinsic dynamics have remained experimentally inaccessible. Here, we directly resolve sub-picosecond edge photocurrent dynamics in WTe$_2$ through ohmic contacts over temperatures from 300 K to 4 K. We demonstrate ultrafast optical-to-electrical conversion with a 3 dB bandwidth of $\sim$250 GHz and reveal picosecond-timescale switching of the net photocurrent direction below 150 K, linked to a Lifshitz transition. This transient bipolar response arises from non-equilibrium Seebeck effects due to asymmetric cooling of hot electrons and holes. These findings reveal previously hidden ultrafast dynamics in symmetry-engineered materials, offering new strategies to disentangle competing photocurrent mechanisms and enabling the development of self-powered, ultrafast optoelectronic devices.
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All authors Subhashri Chatterjee, Katsumasa Yoshioka, Taro Wakamura, Vasili Perebeinos, Norio Kumada

Materials Science

Real-Space Quantification of Exciton Localization in Acene Crystals Using Wannier Function Decomposition

Zui Tao, Jonah B. Haber and Jeffrey B. Neaton

We introduce the Wannier function decomposition of excitons (WFDX) method to quantify exciton localization in solids within the ab initio Bethe-Salpeter equation framework. By decomposing each Bloch exciton wavefunction into products of single-particle electron and hole maximally localized Wannier functions, this real-space approach provides well-defined orbital- and spatial- resolved measures of both Frenkel and charge-transfer excitons at low computational cost. We apply WFDX to excitons in acene crystals, quantifying how the number of rings, the exciton spin state, and the center-of-mass momntum affect spatial localization. Additionally, we show how this real-space representation reflects structural nonsymmorphic symmetries that are hidden in standard reciprocal-space descriptions. We demonstrate how the WFDX framework can be used to efficiently interpolate exciton expansion coefficients in reciprocal-space and outline how it may facilitate evaluation of observables involving position operators, highlighting its potential as a general tool for both analyzing and computing excitonic properties in solids.
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Tuesday 7 October

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

High Strain Rate Behavior of Liquid Crystal Elastomers

Adeline Wihardja, Juan Carlos Nieto Fuentes, Daniel Rittel et al. (+1 more)

Liquid crystal elastomers are rubbery solids that couple liquid crystalline order and deformation. This coupling leads to properties that are attractive for a number of applications in soft robotics and energy absorption. This paper is motivated by the latter application, and provides a systematic experimental study of a particular class of liquid crystal elastomers – the isotropic genesis polydomain liquid crystal elastomers – over a wide range of strain rates. An important aspect of this study is a novel tensile drop-tower that enables tensile strain rates of 100 s$^{-1}$ that are important to application but previously inaccessible. The paper also extends a recently proposed constitutive model to the high strain rate regime, and shows that it can be fit to describe the observed behavior across the spectrum of examined behavior.
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All authors Adeline Wihardja, Juan Carlos Nieto Fuentes, Daniel Rittel, Kaushik Bhattacharya

Materials Science · Cross-listed from cs.DL

Evolve with Your Research – Stepwise System Evolution from Document-driven to Fact-centric Research Data Management in Materials Science

Victor Dudarev and Alfred Ludwig

The digitalisation of research requires data management systems capable of supporting a broad spectrum of usage scenarios, ranging from document-oriented repositories to fully factographic environments. This paper introduces a methodological approach for the stepwise development of such systems, illustrated by the MatInf Research Data Management System (RDMS). The proposed framework combines a graph-based STAR paradigm-emphasising Statefulness, Traceability, Aim, and Result-with the SET methodology, which enables systematic Standardisation, Extraction, and Testing of research data. Together, these principles provide a pathway towards FAIR-compliant data infrastructures, facilitating reproducibility, re-use, and integration of heterogeneous materials science data. By demonstrating the gradual consolidation of research outputs into unified datasets, this study highlights how adaptive RDMS design can support accelerated scientific discovery and enhance collaborative research in large-scale projects.
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Materials Science · Cross-listed from cs.LG

Assessment of different loss functions for fitting equivalent circuit models to electrochemical impedance spectroscopy data

Ali Jaberi, Amin Sadeghi, Runze Zhang et al. (+5 more)

Electrochemical impedance spectroscopy (EIS) data is typically modeled using an equivalent circuit model (ECM), with parameters obtained by minimizing a loss function via nonlinear least squares fitting. This paper introduces two new loss functions, log-B and log-BW, derived from the Bode representation of EIS. Using a large dataset of generated EIS data, the performance of proposed loss functions was evaluated alongside existing ones in terms of R2 scores, chi-squared, computational efficiency, and the mean absolute percentage error (MAPE) between the predicted component values and the original values. Statistical comparisons revealed that the choice of loss function impacts convergence, computational efficiency, quality of fit, and MAPE. Our analysis showed that X2 loss function (squared sum of residuals with proportional weighting) achieved the highest performance across multiple quality of fit metrics, making it the preferred choice when the quality of fit is the primary goal. On the other hand, log-B offered a slightly lower quality of fit while being approximately 1.4 times faster and producing lower MAPE for most circuit components, making log-B as a strong alternative. This is a critical factor for large-scale least squares fitting in data-driven applications, such as training machine learning models on extensive datasets or iterations.
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All authors Ali Jaberi, Amin Sadeghi, Runze Zhang, Zhaoyang Zhao, Qiuyu Shi, Robert Black, Zoya Sadighi, Jason Hattrick-Simpers

Materials Science · Cross-listed from eess.SY

Techno-economic analysis of self-sustainable thermophotovoltaic systems for grid-scale energy generation

Jihun Lim and Sungwon Lee

To facilitate the widespread adoption of renewable energy, dispatchable, zero-emission power sources are essential for grid stability. This work performs a comprehensive techno-economic analysis of a self-sustainable thermophotovoltaic (TPV) system, an architecture that integrates solar charging to function as a standalone power generation asset. Using theory-based models for conventional air-bridge InGaAs and Si diode cells, our analysis reveals that while the system is not currently competitive from a pure levelized of storage cost (LCOS) perspective due to the high capital expenditure for thermal battery materials, its primary value lies in its competitive levelized cost of electricity (LCOE), which is comparable to that of conventional dispatchable generators such as gas turbines. Furthermore, we show that a full Si-based TPV system, utilizing a 50-{\mu}m-thick air-bridge cell for enhanced photon utilization, can also achieve an LCOE that is competitive with such conventional power sources at scales exceeding the gigawatt-hour level, despite its lower conversion efficiency relative to its InGaAs counterpart. This highlights a practical engineering pathway for leveraging the immense manufacturing scalability of Si, offering a lower-risk route to deployment compared to III-V materials. Ultimately, this work establishes the self-sustainable TPV architecture as a compelling pathway toward providing grid-scale, on-demand, zero-emission power.
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Materials Science

High temperature Neel skyrmions in simple ferromagnets

Peng Wang, Rana Saha, Holger L. Meyerheim et al. (+10 more)

A wide variety of chiral non-collinear spin textures have been discovered and have unique properties that make them highly interesting for technological applications. However, many of these are found in complex materials and only in a narrow window of temperature. Here, we show the formation of Neel-type skyrmions in thin layers of simple ferromagnetic alloys, namely Co-Al and Co-Ni-Al, over a wide range of temperature up to 770 K, by imposing a vertical strain gradient via epitaxy with an Ir-Al underlayer. The Neel skyrmions are directly observed using Lorentz transmission electron microscopy in freestanding membranes at high temperatures and the strain gradient is directly measured from x-ray diffraction anomalous peak profiles. Our concept allows simple centrosymmetric ferromagnets with high magnetic ordering temperatures to exhibit hot skyrmions, thereby, bringing closer skyrmionic electronics.
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All authors Peng Wang, Rana Saha, Holger L. Meyerheim, Ke Gu, Hakan Deniz, David Eilmsteiner, Andrea Migliorini, Juan Rubio Zuazo, Engenia Sebastiani-Tofano, Ilya Kostanovski, Abhay Kant Srivastava, Arthur Ernst, Stuart S. P. Parkin

Materials Science

Multimode magnon-phonon cavity driven by symmetry-locked strain fields

Chunli Tang, Yujie Zhu, Dayne Sasaki et al. (+13 more)

Hybrid magnon-phonon cavities with precise control knobs are highly sought after for coherent energy and signal transduction in solid-state platforms. While strain offers a powerful means to tune magnonic characteristics, extending strain engineering into magnon-phonon hybridization has remained elusive. Moreover, implementing controllable strain at the meso- or nanoscale poses a formidable challenge, as spatial inhomogeneity of strain fields often leads to enhanced damping and reduced coherence, thereby hindering device integration and scalability. Here, we present an epitaxial La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) heterostructure that exhibits strong coupling between the Kittel magnon and acoustic phonon. Leveraging the emergence of structural domains when STO undergoes a cubic-to-tetragonal phase transition, we create anisotropic local strains at the interface. Remarkably, the anisotropic local strain of less than 0.1 % drives the pronounced splitting of the magnon into three branches. Each branch independently hybridizes with acoustic phonons, forming a matrix of magnon-phonon avoided crossings that underpins multimode transduction and programmable networks in frequency and magnetic field space. An analytical model reveals that the split magnon branches are deterministically locked to the three main crystalline axes, enabling robust, orientation-selective control of the hybridized magnon-phonon spectrum against spatial inhomogeneity. Our results establish designed local strain as an exceptionally sensitive trigger for multimode magnon-phonon hybridization in magnetoelastic oxide heterostructures, and highlight local strain engineering as a viable strategy for designing tunable hybrid magnonic and phononic devices.
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All authors Chunli Tang, Yujie Zhu, Dayne Sasaki, Jiaxuan Wu, Yuzan Xiong, Harshil Goyal, Masoud Mahjouri-Samani, Mark Adams, Xiang Meng, Bethany E. Matthews, Le Wang, Yingge Du, Jia-Mian Hu, Yayoi Takamura, Wei Zhang, Wencan Jin

Materials Science

Local Order Average-Atom Interatomic Potentials

Chloe A. Zeller, Ronald E. Miller and Ellad B. Tadmor

This article describes an extension to the effective Average-Atom (AA) method for random alloys to account for local ordering (short-range order) effects by utilizing information from partial radial distribution functions. The new Local Order Average-Atom (LOAA) method is rigorously derived based on statistical mechanics arguments and validated for non-stoichiometric binary 2D hexagonal crystals and 3D FeNiCr and NiAl alloys whose ground state is obtained through Monte Carlo sampling. Material properties for these alloys computed from atomistic simulations using standard interatomic potentials (IPs) exhibit a strong dependence on local ordering that is captured by simulations with effective LOAA IPs, but not the original AA method. The advantage of LOAA is that it requires smaller system sizes to achieve statistically converged results and therefore enables the simulation of complex materials, such as high-entropy alloys, at a fraction of the computational cost of standard IPs.
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Materials Science

Mechanistic insights into hydrogen reduction of multicomponent oxides via in-situ high-energy X-ray diffraction

Shiv Shankar, Barak Ratzker, Claudio Pistidda et al. (+2 more)

Co-reduction of multicomponent oxides with hydrogen provides a carbon-neutral approach toward sustainable alloy design. Herein, we investigate the hydrogen-based direct reduction, using in-situ high-energy X-ray diffraction of two precursor variants: mechanically mixed powders and pre-sintered oxide mixtures, targeting an equiatomic CoFeMnNi alloy. We find distinct reduction pathways and microstructure evolution depending on initial precursors. Mixed powders at 700 {\deg}C are reduced to body-centered-cubic, face-centered-cubic, and MnO phases via halite, spinel, and Mn3O4 intermediates, whereas the pre-sintered material directly transforms into a mixture of metallic and oxide phases. The post-reduction microstructures are also different: mixed oxides show loosely packed morphology, whereas pre-sintered material reveals metallic nanoparticles supported on nanoporous MnO. The formation of nanoporous metallic networks is strongly governed by the precursor state, highlighting the role of initial precursors on the final microstructure. This precursor design strategy offers a single-step route to nanoporous alloys with potential applications in catalysis and energy technologies.
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All authors Shiv Shankar, Barak Ratzker, Claudio Pistidda, Dierk Raabe, Yan Ma

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

Kekulé Superconductivity in Twisted Magic Angle Bilayer Graphene

Ke Wang and K. Levin

While it has been one of the most important new physics discoveries in the last decade, the nature of superconductivity in the twisted graphene family remains an unsolved problem. Motivated by recent scanning tunneling experiments that report Kekulé ordering in moiré graphene superconductors, we develop a microscopic theory of this superconductivity for the twisted bilayer system. The pairing we find is an intra-valley, finite-momentum pair-density wave (PDW) that intrinsically carries a Kekulé modulation. This state exhibits four salient features: (i) spontaneous breaking of $C_3$ rotation symmetry, producing nematic order (ii)with triplet pairing; and (iii) a quasiparticle density of states that evolves from a V-shaped profile to a fully gapped, U-shaped spectrum as the attraction increases which is accompanied by (iv) systematic behavior of the temperature dependent zero bias conductance. These features align with key experimental signatures. We find, as well, that with only modest interaction strengths, the state is near to a BEC-like phase, consistent with the observed extremely short coherence lengths. Taken together, these results identify a microscopic intra-valley Kekulé PDW as a compelling candidate for unconventional superconductivity in the twisted graphene family.
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Materials Science

Synthesis and Characterization of Ultrasonically Atomized Al-Based Alloy Powders for Tunable Thermal Reactivity

Chetan Singh, Ava Goglia, Peter Mastracco et al. (+4 more)

Reactive aluminum (Al) alloy powders are promising for advanced manufacturing, joining, and energetic applications, yet scalable routes that couple controlled reactivity with safe handling remain limited. While nanoscale Al powders ignite readily, their agglomeration, handling, and safety limit broad deployment. Here, we manufacture micron-sized Al-based powders produced by ultrasonic atomization (UA), targeting a balance of enhanced reactivity and process robustness. Binary systems (AlCu, AlSi, AlMg) and pure Al were synthesized, and their morphology, phases present, thermal stability, and oxidation behavior were characterized using XRD, SEM, and DTA/TGA in an Ar/O2 environment. We show that alloy selection and UA-controlled microstructure can modify the native Al2O3 passivation, alter oxidation pathways, and shift thermal onsets/exotherms. The results establish a manufacturing-forward framework for designing micron-sized powders with tunable ignition/oxidation behavior.
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All authors Chetan Singh, Ava Goglia, Peter Mastracco, Michael Flickinger, Laszlo J. Kecskes, Paulette Clancy, Timothy P. Weihs

Materials Science

Emergence of multiple relaxation processes during low to high density transition in Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glass

Alberto Ronca, Antoine Cornet, Jie Shen et al. (+8 more)

The existence of multiple amorphous states, or polyamorphism, remains one of the most debated phenomena in disordered matter, particularly regarding its microscopic origin and impact on glassy dynamics. Profiting of the enhanced data quality provided by brilliant synchrotrons, we combined high pressure X-ray photon correlation spectroscopy and X-ray diffraction to investigate the atomic dynamics-structure relationship in a Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glass at room temperature. We identify a structural and dynamical crossover near 3 GPa, marked by avalanches-like massive atomic rearrangements that promote the system toward increasingly compact atomic cluster connections. This crossover superimposes to a pressure-induced acceleration of the atomic motion recently reported, and signals the onset of a transitional state, potentially linked to the nucleation of a new phase within the glass, characterized by the coexistence of two amorphous states with distinct relaxation processes. These results provide evidence for a sluggish, continuous polyamorphic transformation, even in absence of marked structural discontinuities.
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All authors Alberto Ronca, Antoine Cornet, Jie Shen, Thierry Deschamps, Eloi Pineda, Yuriy Chushkin, Federico Zontone, Mohamed Mezouar, Isabella Gallino, Gaston Garbarino, Beatrice Ruta

Materials Science · Cross-listed from quant-ph

Prediction of Molecular Single-Photon Emitters: A Materials-Modelling Approach

Erik Karlsson Öhman, Daqing Wang, R. Matthias Geilhufe et al. (+1 more)

Interfacing light with quantum systems is an integral part of quantum technology, with the most essential building block being single-photon emitters. Although various platforms exist, each with its individual strengths, molecular emitters boast a unique advantage – namely the flexibility to tailor their design to fit the requirements of a specific task. However, the characteristics of the vast space of possible molecular configurations are challenging to understand and explore. Here, we present a theoretical and computational framework to initiate exploration of this vast potential by integrating database analysis with microscopic predictions. Using a model system of dibenzoterrylene in an anthracene host as benchmark, our approach identifies promising new candidates, among them a chiral molecular emitter. Future extensions of our approach integrated with machine learning routines hold the promise of ultimately unlocking the full potential of molecular quantum light-matter interfaces.
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All authors Erik Karlsson Öhman, Daqing Wang, R. Matthias Geilhufe, Christian Schäfer

Materials Science

Multihyperuniform Particle Composites Inspired by Avian Photoreceptor Patterns for Optical Applications

David Keeney, Wenlong Shi, Rohit Thomas et al. (+1 more)

Hyperuniform materials, characterized by anomalously suppressed long-wavelength density fluctuations, exhibit unique optical and photonic properties distinct from both crystalline and random media. While most prior studies have focused on single-species systems, we investigate the broader class of multihyperuniform systems inspired by biological photoreceptor mosaics. Using particle-based models with varying species number, size ratios, and interaction competition, we demonstrate that multispecies mixtures can achieve robust and stealthy hyperuniform configurations, even in highly disordered states. We further show how these configurations can be mapped to multifunctional composites with tailored optical responses, including isotropic structural coloration, enhanced absorption, and engineered dielectric properties that facilitate transmission while suppressing scattering. Our results highlight multihyperuniformity as a generalizable design principle for multifunctional disordered photonic materials, opening avenues for robust, tunable, and scalable optical applications.
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All authors David Keeney, Wenlong Shi, Rohit Thomas, Yang Jiao

Materials Science

Enhancing Direct Air Capture through Potassium Carbonate Doping of Activated Carbons

N. van Dongen, A. J. F. van Hoof, S. Calero et al. (+1 more)

Direct air capture of carbon dioxide (CO$_2$) is one of the most promising strategies to mitigate rising atmospheric CO$_2$ levels. Among various techniques, adsorption using porous materials is a viable method for extracting CO$_2$ from air, even under humid conditions. However, identifying optimal adsorbent materials remains a significant challenge. Moreover, the performance of existing materials can be improved by doping with active species that boost gas capture, a relatively unexplored field. In this study, we perform atomistic simulations to investigate the adsorption, structural, and energetic properties of CO$_2$ and water in realistic models of activated carbons. We first analyze the impact of explicitly considering surfaces containing functional groups, which aims to imitate the chemical environment of experimental samples. Additionally, we introduce potassium carbonate within the pores of the adsorbent to evaluate its effect on CO$_2$ and water adsorption. Our results demonstrate that both functional groups and potassium carbonate enhance adsorption, primarily by shifting the adsorption onset pressures to lower values. Specifically, potassium carbonate clusters act as extra adsorption sites for CO$_2$ and water, facilitating the nucleation of water molecules and promoting the formation of a hydrogen bond network within the activated carbon pores.
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All authors N. van Dongen, A. J. F. van Hoof, S. Calero, J. M. Vicent-Luna

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

Frieze charge-stripes in a correlated kagome superconductor CsCr$_3$Sb$_5$

Siyu Cheng, Keyu Zeng, Yi Liu et al. (+4 more)

Kagome metals have developed into a vibrant playground for materials physics, where geometric frustration, electronic correlations and band topology come together to create a variety of exotic phenomena. Recently synthesized CsCr$_3$Sb$_5$ has provided a rare opportunity to explore unconventional superconductivity in a strongly correlated kagome system with hints of frustrated magnetism and quantum criticality. Using spectroscopic imaging scanning tunneling microscopy, we reveal a cascade of density wave transitions with different symmetries in bulk single crystals of CsCr$_3$Sb$_5$. In particular, we discover a new electronic state $-$ a unidirectional density wave that breaks all mirror symmetries akin to a chiral density wave, but in contrast retains a mirror-glide symmetry. We term this state a frieze charge-stripe order phase, because its symmetry properties agree with one of the fundamental frieze symmetry groups. A combination of high-resolution imaging, Fourier analysis and theoretical simulations uncovers the crucial role of sublattice degrees of freedom in forming this phase, with internal chiral textures of opposite handedness. Our experiments reveal that superconductivity in CsCr$_3$Sb$_5$ develops from a new type of a unidirectional density wave, and set the foundation for exploring electronic states with frieze symmetry groups in quantum materials.
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All authors Siyu Cheng, Keyu Zeng, Yi Liu, Christopher Candelora, Ziqiang Wang, Guang-Han Cao, Ilija Zeljkovic

Materials Science

Bridging the Synthesizability Gap in Perovskites by Combining Computations, Literature Data, and PU Learning

Rushik Desai, Junyeong Ahn, Alejandro Strachan et al. (+1 more)

Among emerging energy materials, halide and chalcogenide perovskites have garnered significant attention over the last decade owing to the abundance of their constituent species, low manufacturing costs, and their highly tunable composition-structure-property space. Navigating the vast perovskite compositional landscape is possible using density functional theory (DFT) computations, but they are not easily extended to predictions of the synthesizability of new materials and their properties. As a result, only a limited number of compositions identified to have desirable optoelectronic properties from these calculations have been realized experimentally. One way to bridge this gap is by learning from the experimental literature about how the perovskite composition-structure space relates to their likelihood of laboratory synthesis. Here, we present our efforts in combining high-throughput DFT data with experimental labels collected from the literature to train classifier models employing various materials descriptors to forecast the synthesizability of any given perovskite compound. Our framework utilizes the positive and unlabeled (PU) learning strategy and makes probabilistic estimates of the synthesis likelihood based on DFT- computed energies and the prior existence of similar synthesized compounds. Our data and models can be readily accessed via a Findable, Accessible, Interoperable, and Reproducible (FAIR) nanoHUB tool.
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All authors Rushik Desai, Junyeong Ahn, Alejandro Strachan, Arun Mannodi-Kanakkithodi

Materials Science

Origin of trapped intralayer Wannier and charge-transfer excitons in moiré materials

Indrajit Maity, Johannes Lischner, Arash A. Mostofi et al. (+1 more)

Moiré materials offer a versatile platform for engineering excitons with unprecedented control, promising next-generation optoelectronic applications. While continuum models are widely used to study moiré excitons due to their computational efficiency, they often disagree with ab initio many-body approaches, as seen for intralayer excitons in WS$_2$/WSe$_2$ heterobilayers. Here, we resolve these discrepancies using an atomistic, quantum-mechanical framework based on the Bethe-Salpeter equation with localized Wannier functions as the basis for the electronic structure. We show that inclusion of dielectric screening due to hexagonal boron nitride (hBN) encapsulation is essential to reproduce the full set of experimentally observed features of moiré intralayer excitons. Our analysis reveals a competition between Wannier and charge transfer characters, driven by variations between direct and indirect band gaps at high symmetry stacking regions due to atomic relaxations and environmentally tunable electron-hole interactions. Building on this insight, we demonstrate that the lowest-energy bright excitons are Wannier-like in WS2/WSe2 heterobilayers but charge-transfer-like in twisted WSe2 homobilayers, despite having comparable moiré lengths when encapsulated in hBN. In the absence of hBN encapsulation, the lowest-energy bright exciton in twisted WSe$_2$ becomes Wannier-like. These results establish atomistic modeling as a powerful and efficient approach for designing and controlling excitonic phenomena in moiré materials.
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All authors Indrajit Maity, Johannes Lischner, Arash A. Mostofi, Ángel Rubio

Materials Science

Colorimetry and Tribology of Ultrapure Copper Surface Micromodification

Aleksandra Szczupak, Grzegorz Cios and Benedykt R. Jany

Controlling optical and tribological properties of metal surfaces, like color and wear rate, without altering their chemical composition is a highly desirable process across numerous fields of science and industry. It represents a cost-effective alternative to traditional chemical methods, particularly for copper, one of the most important metals widely used where high electrical and thermal conductivity, alongside resistance to corrosion, are required. We investigated the control of copper surface texture through a controlled micromodification process, utilizing constant force and velocity with abrasive silicon carbide sandpaper on ultrapure copper pellets exhibiting elongated crystallographic grains, and its impact on optical properties. Systematically varying grit size and rubbing direction, both along and across the grains, resulted in tunable microgroove morphology, demonstrating a marked difference in wear rate between single-grain and multi-grain abrasion. Furthermore, modification along copper grain boundaries yielded a change in the wear rate by a factor of two, related to single-grain and multi-grain abrasion regime changes, enabling precise control over material performance via tuned abrasion conditions. Colorimetric analysis via C-Microscopy revealed a strong, statistically significant relationship between abrasive parameters, microgroove geometry (inclination angle, depth, and size), and optical spectral signatures, which were then parametrized to achieve targeted control. This research demonstrates a simple yet effective approach to color and reflectance modification via microgroove engineering, offering a pathway to customized material properties by uniquely coupling contact mechanics, surface morphology, and colorimetry at the microscale level.
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Materials Science · Cross-listed from physics.chem-ph

Adaptive Pruning for Increased Robustness and Reduced Computational Overhead in Gaussian Process Accelerated Saddle Point Searches

Rohit Goswami and Hannes Jónsson

Gaussian process (GP) regression provides a strategy for accelerating saddle point searches on high-dimensional energy surfaces by reducing the number of times the energy and its derivatives with respect to atomic coordinates need to be evaluated. The computational overhead in the hyperparameter optimization can, however, be large and make the approach inefficient. Failures can also occur if the search ventures too far into regions that are not represented well enough by the GP model. Here, these challenges are resolved by using geometry-aware optimal transport measures and an active pruning strategy using a summation over Wasserstein-1 distances for each atom-type in farthest-point sampling, selecting a fixed-size subset of geometrically diverse configurations to avoid rapidly increasing cost of GP updates as more observations are made. Stability is enhanced by permutation-invariant metric that provides a reliable trust radius for early-stopping and a logarithmic barrier penalty for the growth of the signal variance. These physically motivated algorithmic changes prove their efficacy by reducing to less than a half the mean computational time on a set of 238 challenging configurations from a previously published data set of chemical reactions. With these improvements, the GP approach is established as, a robust and scalable algorithm for accelerating saddle point searches when the evaluation of the energy and atomic forces requires significant computational effort.
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Materials Science

Spin wave theory for the triaxial magnetic anisotropy 2D van der Waals antiferromagnet CrSBr

Sergio M. Rezende, Byron Freelon and Roberto L. Rodríguez-Suárez

The magnetic properties of two-dimensional (2D) materials have been attracting increasing attention in recent years due to their unique behavior and possible applications in new devices. One material of great interest is the 2D van der Waals (vdW) crystal CrSBr, that exhibits antiferromagnetic (AF) order at low temperatures due to an interlayer AF exchange interaction. Here we present a full quantum spin-wave theory for CrSBr considering three intralayer and one interlayer exchange interactions, and triaxial magnetic anisotropy. The fits of the theoretical results to antiferromagnetic resonance (AFMR) measurements and inelastic neutron scattering data yield reliable values for the seven interaction parameters that can be used to calculate other properties of this interesting material.
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