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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Thursday 5 March

Materials Science

Large-scale Integration of Experimental and Computational Data for 2D Materials

Mohammad A. Akhound, Tara M. Boland, Mikkel O. Sauer et al. (+19 more)

The past decade has seen rapid growth in the number of experimentally realized two-dimensional (2D) materials with diverse chemical and physical properties. However, information on their crystal structure, synthesis routes, and measured or predicted properties, remains scattered across thousands of publications. Here we consolidate this fragmented knowledge by establishing X2DB - an open infrastructure that integrates experimental and computational data on 2D materials. Using extensive literature mining and direct community uploads, we identify 370 unique 2D materials that have been realized in monolayer or few-layer form, and link them to their digital counterparts in computational databases, enabling consistent ab initio characterization of their properties across monolayer, bilayer and bulk forms. We describe the structure and content of the database highlighting its support for community uploads, illustrate how it can be used to generate new scientific insight and introduce a hierarchical classification of the known set of 2D materials. Our work provides a foundation for the integration and cross-fertilization of experimental and theoretical knowledge, opening new avenues for data-driven, predictive synthesis of novel 2D materials.
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All authors Mohammad A. Akhound, Tara M. Boland, Mikkel O. Sauer, Matthias Batzill, Moses A. Bokinala, Stela Canulescu, Yury Gogotsi, Philip Hofmann, Andras Kis, Jiong Lu, Thomas Michely, Søren Raza, Wencai Ren, Joshua A. Robinson, Zdenek Sofer, Jing H. Teng, Søren Ulstrup, Meng Zhao, Xiaoxu Zhao, Jens J. Mortensen, Thomas Olsen, Kristian S. Thygesen

Materials Science

Ab initio quasi-harmonic thermoelasticity, piezoelectricity, and thermoelectricity of polar solids at finite temperature and pressure: Application to wurtzite ZnO

Xuejun Gong and Andrea Dal Corso

We generalize a previously established ab initio approach-originally developed for hexagonal close-packed (hcp) metals-to accommodate solids with both internal and external degrees of freedom. This extension enables the thermodynamic and thermoelastic characterization of insulators, including those with non-vanishing piezoelectric and pyroelectric tensors. Utilizing Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) within the quasi-harmonic approximation, we derive the pressure and temperature dependence of these properties. Specifically, we investigate internal degrees of freedom using two distinct frameworks: the Zero Static Internal Stress Approximation (ZSISA) and Full Free Energy Minimization (FFEM). We then compare these approximations by computing internal and external thermal expansions, as well as temperature-dependent piezoelectric and pyroelectric tensors. Finally, we demonstrate the generalized formalism by calculating the thermodynamic properties of wurtzite ZnO across a broad range of pressures and temperatures.
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Materials Science · Cross-listed from physics.optics

Real-Space Plasmon Imaging Reveals Modified Electronic Structure of Gold at the Monolayer Limit

Andrei Bylinkin, Philippe Roelli, Naveen Shetty et al. (+8 more)

Atomically thin materials exhibit electronic and optical properties distinct from their three-dimensional counterparts. For metals, particularly gold, monolayer studies remain largely unexplored due to fabrication and characterisation challenges. Here we report the first optical study of a stable quasi-freestanding gold monolayer formed by Au intercalation between graphene and SiC. Mid-infrared nanoimaging reveals plasmon-polaritons with wavelengths nearly an order of magnitude shorter than free-space light. Analysis of their dispersion using a Drude model yields a relaxation time of $\tau = 18\,$fs, comparable to bulk gold, and a Drude weight of $D = 1.3\,$mS$\cdot$eV, nearly twice the bulk expectation. These results establish monolayer gold as a two-dimensional metal, opening opportunities for nanoscale photonics, plasmonics and ultra-thin electronics.
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All authors Andrei Bylinkin, Philippe Roelli, Naveen Shetty, Rositsa Yakimova, Ulrich Starke, Camilla Coletti, Stiven Forti, Alexei Zakharov, Vyacheslav M. Silkin, Samuel Lara-Avila, Rainer Hillenbrand

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

Systematic study of superconductivity in few-layer $T_d$-MoTe$_2$

Taro Wakamura, Masayuki Hashisaka, Yusuke Nomura et al. (+7 more)

We present a systematic investigation of superconductivity in a topological superconductor candidate $T_{\rm d}$-MoTe$_2$ in the few-layer limit. By examining multiple mechanically exfoliated samples with different thicknesses, substrates and crystal qualities, we quantitatively correlate superconducting temperature ($T_c$) with disorder, carrier density, carrier type and mobility. By integrating these experimental findings with first-principles calculations, we reveal the relationship between the band structure and superconductivity in this material. Notably, in 2 L samples we access a highly hole-doped regime that has not been systematically explored in previous experiments, providing a complementary perspective to earlier studies. In this regime, we demonstrate that superconductivity can be realized in a manner consistent with a conventional phonon-mediated $s_{(++)}$-wave pairing.
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All authors Taro Wakamura, Masayuki Hashisaka, Yusuke Nomura, Matthieu Bard, Shota Okazaki, Takao Sasagawa, Takashi Taniguchi, Kenji Watanabe, Koji Muraki, Norio Kumada

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

Extended dynamical density functional theory for nonisothermal binary systems including momentum density

Michael te Vrugt, Hartmut Löwen, Helmut R. Brand et al. (+1 more)

In order to describe the nonisothermal dynamics of two-phase flows or binary mixtures such as colloidal suspensions consisting of colloidal particles and solvent on a microscopic level, we derive a new extended dynamical density functional theory (EDDFT) that includes the total mass density, the local concentration of one species, the total momentum density, and the energy density as variables using the Mori-Zwanzig-Forster projection operator technique. Through the incorporation of the momentum density into EDDFT, not only the diffusive but also the convective dynamics is taken into account. We derive an exact entropy and free-energy functional for the case of hard spheres. The hydrodynamic limit of our new EDDFT and its relation to the mode-coupling theory of the glass transition are discussed. It is shown that EDDFT allows to obtain the correct value for the speed of sound.
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All authors Michael te Vrugt, Hartmut Löwen, Helmut R. Brand, Raphael Wittkowski

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

Modular memristor model with synaptic-like plasticity and volatile memory

Daniel Habart, Stephen H. Foulger, Kristyna Kovacova et al. (+5 more)

Compact models of memristors are essential for simulating large-scale neuromorphic systems, yet they often do not include description of complex dynamics like volatile relaxation and synaptic plasticity. We introduce a modular, computationally efficient memristor model that bridges this gap by integrating principles from physics and computational neuroscience. The model defines a framework consisting of a standard formulation of memristive device dynamics, a functional rule mapping state variables to cumulative conductance, a volatility module inspired by the theory of linear viscoelasticity and a saturation module implementing a linear-nonlinear technique. Additionally, we develop a formulation of synaptic-like plasticity inspired by a biological spike-timing-dependent plasticity (STDP) rule, which is compatible with the general framework for memristive devices. Finally, we propose a Laplace transform-based technique to derive the precise form of the mapping from state variables to cumulative conductance, replacing ad hoc voltage-current relationships with principled construction. We quantitatively validate the complete model against a rich set of experimental data from polymeric memristors exhibiting potentiation, synaptic-like plasticity and volatile decay. Our work presents a new paradigm for memristor modeling that is both practical for large-scale simulation and rich in explanatory power, providing a principled tool for the design of next-generation neuromorphic hardware.
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All authors Daniel Habart, Stephen H. Foulger, Kristyna Kovacova, Ambika Pandey, Yadu R. Panthi, Jiri Pfleger, Jarmila Vilcakova, Lubomir Kostal

Materials Science

Energy conservation and pressure relaxation in an extended two-temperature model for copper with an electron temperature-dependent interaction potential

Simon Kümmel and Johannes Roth

An implementation of an electron temperature-dependent interaction potential for copper in a two-temperature model-molecular dynamics framework is presented. An algorithm for enforcing energy conservation when using such an interaction is provided that is needed due to the changing interaction strength with the degree of excitation. Furthermore, focus is put on how to treat the pressure differences due to an electron temperature gradient following laser irradiation. The influence of various extensions is investigated in large-scale two-temperature model molecular dynamics simulations and compared to existing approaches.
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Materials Science · Cross-listed from cond-mat.stat-mech

A minimal electrostatic theory for the Seebeck coefficient in liquids

Wataru Kobayashi

The Seebeck coefficient in liquids often reaches the mV/K range, yet its microscopic origin remains unclear due to the complexity of electrolyte systems. Here we propose a minimal electrostatic theory focusing on solvation entropy. Using a core-shell extension of the Born equation with temperature-dependent dielectric response, we provide an alternative electrostatic interpretation of the mV/K-scale solvent-structuring contribution extracted for a cobalt redox electrolyte. The theory clarifies that large valence, small cationic radius, small dielectric constant, and large magnitude of $\frac{d\varepsilon}{dT}$ are key factors for enhanced liquid Seebeck response.
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Materials Science

Design rules for industrial-scale sintering of UB4-UBC composites with high uranium density

Riley Moeykens, Anthony Albert-Harrup, David Simonne et al. (+2 more)

Uranium borides are promising candidate fuel forms for use in advanced nuclear reactors due to their high thermal conductivity and potential for dual use as both fuel and burnable absorber materials. In this work, uranium tetraboride (UB$_4$) and uranium monoboroncarbide (UBC) composites were synthesized using an industrially scalable borocarbothermic reduction method. The high-temperature structural evolution of the as-synthesized borides was investigated using in situ synchrotron X-ray diffraction (SXRD). The oxidation behavior was further characterized using a combination of SXRD and thermogravimetric analysis (TGA), allowing direct comparison with other potential accident-tolerant fuels such as UB$_2$, U$_3$Si$_2$, UC, and UN. The UB$_4$-UBC composite shows higher uranium loading than monolithic UB$_4$ and demonstrates promising oxidation behavior at elevated temperature, pointing to its potential as an improved uranium boride-based fuel form.
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All authors Riley Moeykens, Anthony Albert-Harrup, David Simonne, Mehmet Topsakal, Ericmoore Jossou

Materials Science

Damage Prediction of Sintered {\alpha}-SiC Using Thermo-mechanical Coupled Fracture Model

Jason Sun, Yu Chen, Joseph J. Marziale et al. (+3 more)

A three-way coupled thermo-mechanical fracture model is presented to predict the damage of brittle ceramics, in particular {\alpha}-SiC, over a wide range of temperatures (20-1400 C). Predicting damage over such a range of temperatures is crucial for thermal protection systems for many systems such as spacecraft. The model, which has been implemented in MOOSE, is divided into three modules: elasticity, damage phase field, and heat conduction. Analytical approaches for determining crack length scales are presented for both simple tension and simple shear. Validation tests are conducted for both flexural strength and fracture toughness over the specified range of temperatures. Flexural strength simulation results fall within the uncertainty region of the experimental data, and mode I fracture toughness simulation results are also in agreement with the experimental data. Mode II and mixed mode fracture toughness simulations results are presented with the modified G-criterion. Finally, the parallel computing capabilities of the model is considered in various scalability tests.
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All authors Jason Sun, Yu Chen, Joseph J. Marziale, Eric A. Walker, David Salac, James Chen

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

Orbital-Selective Spin-Orbit Mott Insulator in Fractional Valence Iridate La$_3$Ir$_3$O$_{11}$

Kai Wang, Jun Yang, Chaoyang Kang et al. (+5 more)

The combination of strong spin-orbit coupling and Coulomb interactions makes the $5d$ iridates a unique platform for realizing novel correlated electronic states. Here, utilizing infrared spectroscopy, we demonstrate that a robust Mott insulating state persists in the $1/3$-hole self-doped system La$_3$Ir$_3$O$_{11}$, evidenced by the collapse of the Drude response and the emergence of sharp excitations across the Mott gap. Our theoretical calculations reveal that the insulating behavior arises from the cooperative interplay of structural distortions, spin-orbit coupling, and Coulomb interactions. Specifically, octahedral distortion and Ir-Ir dimerization split the $t_{2g}$ orbitals, driving the $J_{\mathrm{eff}} = 1/2$ bands toward half-filling while keeping the $J_{\mathrm{eff}} = 3/2$ bands away from it. Consequently, electron correlations induce an orbital-selective Mott transition in the $J_{\mathrm{eff}} = 1/2$ bands, whereas a band-insulating gap develops in the $J_{\mathrm{eff}} = 3/2$ bands, thereby stabilizing the unconventional insulating state in La$_3$Ir$_3$O$_{11}$. These findings provide new insights into the design and understanding of the insulating ground state of spin-orbit-coupled iridates.
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All authors Kai Wang, Jun Yang, Chaoyang Kang, Weikang Wu, Wenka Zhu, Jianzhou Zhao, Yaomin Dai, Bing Xu

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

Spectroscopic evidence of disorder-induced quantum phase transitions in monolayer Fe(Te,Se) superconductor

Guanyang He, Ziqiao Wang, Longxin Pan et al. (+5 more)

The superconductor-insulator transition as a paradigm of quantum phase transitions has attracted tremendous interest over the past three decades. While the magnetic field and carrier density can be tuned to drive the transition, the role of disorder in the transition is not well understood due to the complicated interplay between superconductivity and electron localization. In this work, we controllably introduce disorder in a two-dimensional high-temperature superconductor by depositing iron clusters onto the superconducting monolayer Fe(Te,Se) crystalline film. The spectral evolution from superconducting gaps to insulating gaps with increasing disorder is detected by scanning tunneling spectroscopy measurements. When the disorder is strong, large U-shaped gaps are observed and attributed to the localization-enhanced Cooper pair correlation. Our observations provide the insight into the emergent phases of low-dimensional and high-temperature superconductors with disorder.
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All authors Guanyang He, Ziqiao Wang, Longxin Pan, Yuxuan Lei, Fa Wang, Yi Liu, Nandini Trivedi, Jian Wang

Wednesday 4 March

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

Quantifying the Features of an Amorphous Solid's Local Yield Surface

Spencer Fajardo, Paul Desmarchelier, Sylvain Patinet et al. (+1 more)

In two-dimensional Lennard-Jones glasses, mechanical probing reveals that local yield surfaces are dominated by regions with a positive second derivative of the yield stress with respect to the loading angle. Each feature corresponds to a shear transformation zone and a characteristic non-affine displacement field at yield. Most features are well described by a combined Schmid-Mohr-Coulomb criterion parameterized by a weak-plane orientation, a critical stress, and a pressure sensitivity. The resulting parameter statistics clarify how the onset of plastic flow is governed by the population of discrete yielding features encoded in the amorphous structure.
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All authors Spencer Fajardo, Paul Desmarchelier, Sylvain Patinet, Michael L. Falk

Materials Science

High pressure melt dynamics in shock-compressed titanium

Saransh Singh, Reetam Paul, Nikhil Rampal et al. (+22 more)

We study the high-pressure melting behavior of titanium using laser-driven shock compression with in situ femtosecond x-ray diffraction and molecular-dynamics simulations based on a machine-learned interatomic potential. The MD simulations predict the solid-liquid coexistence on the Hugoniot in the $\sim$$111-124$ GPa range. Experimentally, we observe the first evidence of liquid at 86 GPa. We also observe pronounced microstructural changes with pressure with strong grain refinement associated with the emergence of liquid, within the solid-liquid coexistence ($\sim$$110-126$ GPa). Above 126 GPa, we observe the persistence of residual levels of highly textured crystalline Ti to $\sim$$180$ GPa, well above the expected melt completion pressure. We discuss the accuracy that current laser-shock experimental platforms have at determining the melt onset and completion pressures.
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All authors Saransh Singh, Reetam Paul, Nikhil Rampal, Rhys J. Bunting, Sebastien Hamel, Nathan Palmer, Christopher P. McGuire, Samantha M. Clarke, Amy Coleman, Cara Vennari, Trevor M. Hutchinson, \\Kimberly A. Pereira, Bob Nagler, Dimitri Khaghani, Hae Ja Lee, Nicholas A. Czapla, Travis Volz, Ian K. OCampo, James McNaney, Thomas E. Lockard, Jon H. Eggert, Amy Lazicki, Christopher E. Wehrenberg, Andrew Krygier, Raymond F. Smith

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

Large-Area Deterministic Stamping of 2D Materials on Arbitrarily Patterned Surfaces

Bernardo S. Dias, Reynolds Dziobek-Garrett, Gabriella Mentasti et al. (+6 more)

2D materials and their monolayers have attracted widespread interest by virtue of their unique electronic and optical properties. In addition to their remarkable physical characteristics, their atomically thin nature enables their integration in ultra-compact photonic and electronic devices, with potential for dynamic tunability via strain, charge carrier modulation or heterostructure engineering. While early research relied on micrometer-scale mechanically exfoliated flakes, recent advances, particularly gold-assisted exfoliation of transition metal dichalcogenides (TMDCs), have enabled the preparation of high-quality, large-area monolayers, opening new opportunities for scalable device integration. For the field of nanophotonics in particular, the ability to transfer large-area 2D materials onto both flat and patterned substrates is essential for the development of functional devices. However, existing transfer techniques are often limited in scalability, and compatibility with structured surfaces. Here, we present a versatile and reliable transfer method of large-area monolayers and hBN/monolayer heterostructures onto both flat and nanostructured substrates. Our approach, based on the physical properties of low-density polyethylene, preserves the intrinsic optical quality of the materials and is compatible with a variety of device architectures. We demonstrate its applicability by fabricating devices that modulate the photoluminescence of TMDC monolayers through the manipulation of the photonic environment, strain or electrical gating. We further demonstrate the fabrication of van der Waals heterostructures using the same method. By enabling clean transfer of a wide range of monolayers and heterostructures, this technique offers a practical pathway for the development of next-generation optoelectronic platforms with improved functionality, scalability, and tunability.
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All authors Bernardo S. Dias, Reynolds Dziobek-Garrett, Gabriella Mentasti, Abhishek Gupta, Alexander Lambertz, Esther Alarcon-Llado, Peter Schall, Roland Bliem, Jorik van de Groep

Materials Science

Moire Topological Magnetism Twist-Engineered from 2D Spin Spirals

Zhonglin He, Kaiying Dou, Wenhui Du et al. (+3 more)

Topological magnetism, characterized by topologically protected spin textures, offers rich physics and transformative prospects for spintronics. However, its stabilization typically demands external magnetic fields, preventing straightforward implementation. Here, we report a universal field-free approach for engineering 2D topologically-trivial spin spirals into topological magnetisms. This approach leverages twisted antiferromagnetic bilayers, where locked spin spirals in the two sublayers form spatially alternating ferromagnetic and antiferromagnetic domains upon twisting. These domains frustrate the uniform antiferromagnetic interlayer exchange, spontaneously stabilizing moire topological magnetisms without external fields. Using first-principles and atomistic spin-model simulations, we validate this approach using bilayers NiCl2 and NiBr2, as representative examples. For twisted NiCl2, we predict topological spin states tunable by the twist angle, including isolated and high-order antiferromagnetic bimerons. For twisted NiBr2, strong frustration yields trivial triple-q spin spirals, which transform into moire topological magnetism with the application of vertical compressive strain. Our findings demonstrate that topologically non-trivial spin textures can be engineered from their trivial counterparts, thus providing a new paradigm for topological spintronics
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All authors Zhonglin He, Kaiying Dou, Wenhui Du, Ying Dai, Evgeny Y. Tsymbal, Yandong Ma

Materials Science

Rapid modeling of segregation-driven metal-oxide adhesion in high-entropy alloys using macroscopic atom model

Dennis Boakye and Chuang Deng

Accurate prediction of metal-oxide adhesion in high-entropy alloys (HEAs) is challenging because interfacial segregation, atomic environments, and macroscopic thermodynamic quantities are strongly correlated. Relying solely on first-principles approaches is too expensive for exploring composition, solute concentration, and co-segregation effects. To address this, we extend the macroscopic atom model (MAM) for multicomponent alloys using composition-consistent surface fractions and an interfacial pair-probability formalism that captures deviations from random contact statistics. Applied to CoCrFeNi (AlCoCrFeNi) HEA in contact with Cr2O3 (Al2O3), the model predicts segregation energies and work of separation as continuous functions of composition, reproducing the correct segregation hierarchy of Hf, Y, Zr, and S. The stronger segregation tendency at Al2O3 interfaces, and the non-linear dependence of surface energy and adhesion on solute content and co-segregation is also captured. The results are benchmarked with DFT calculations, which shows consistent trends, particularly the strengthening of adhesion by Hf and Zr through strong metal-oxygen bonding and the weakening effect of S. These results demonstrate that the extended MAM provides a physically interpretable, computationally efficient, and quantitatively predictive framework for screening segregation-controlled adhesion beyond the limits of DFT.
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Materials Science

Raman scattering spectroscopic observation of a ferroelastic crossover in bond-frustrated PrCd$_3$P$_3$

Jackson Davis, Jesse Liebman, Dibyata Rout et al. (+3 more)

2D magnetism in triangular lattices has already shown potential for hosting exotic magnetic states. Control of these magnetic states, both in terms of magnetic properties and in terms of charge doping would be the next step. This makes materials which combine triangular lattice magnetic layers with layers hosting interesting structural or electronic properties particularly useful. PrCd$_3$P$_3$, studied in this work, is one of a family of materials where triangular lattice layers of magnetic rare earth ions alternate with semiconducting hexagonal CdP layers. Using Raman scattering spectroscopy we uncover a structural instability in the CdP layers, associated with a soft mode behavior of a phonon in these layers. Raman scattering detects crystal electric field excitations, and confirms a singlet ground state for Pr$^{3+}$ and splitting of the doublet levels as a result of the structural instability in CdP layers. While Pr$^{3+}$ is non-magnetic in PrCd$_3$P$_3$ we speculate that this family of materials can realize control of the magnetic layer through the CdP layer which can become ferroelectric under strain that would relieve frustration.
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All authors Jackson Davis, Jesse Liebman, Dibyata Rout, S.J. Gomez Alvarado, Stephen D. Wilson, Natalia Drichko

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

Giant Magnetocrystalline Anisotropy in Honeycomb Iridate NiIrO3 with Large Coercive Field Exceeding 17 T

Chuanhui Zhu, Pengfei Tan, Xiao-Sheng Ni et al. (+13 more)

The realization of unconventional quantum phases in frustrated and spin-orbit coupled materials remains at the forefront of quantum materials research. Here we report the synthesis and discovery of NiIrO3, the first honeycomb iridate with coupled 3d-5d magnetic sublattices, through a soft topotactic reaction. Structural analysis reveals an ilmenite-type stacking of edge-sharing NiO6 and IrO6 octahedral honeycomb sublattices in a Kitaev geometry. Comprehensive magnetic and electrical transport measurements unveil its long-range ferrimagnetic order below 213 K, which is in sharp contrast to the predominantly antiferromagnetic order in the known honeycomb iridates. Notably, the titled compound displays an exceptionally large magnetocrystalline anisotropy energy of 32.2 meV/f.u. and a giant coercivity with coercive field exceeding 17.3 T below 4.2 K, both ranking among the highest observed in iridates to date. Combined experimental and theoretical investigations indicate that the exceptional anisotropy and coercivity originate from the synergistic effect between strong lattice frustration in the coupled 3d-5d honeycomb lattice network and the robust spin-orbit coupling of the Ir4+ (Jeff = 1/2) state. This work positions NiIrO3 as a promising platform to investigate low-dimensional and frustrated quantum spin systems, and highlights its potential for spintronic applications through the targeted engineering of 3d-5d interactions.
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All authors Chuanhui Zhu, Pengfei Tan, Xiao-Sheng Ni, Jingchun Gao, Yuting Chang, Mei-Huan Zhao, Zheng Deng, Shuang Zhao, Tao Xia, Jinjin Yang, Changqing Jin, Junfeng Wang, Chengliang Lu, Yisheng Chai, Dao-Xin Yao, Man-Rong Li

Materials Science · Cross-listed from physics.optics

Realizing anomalous Floquet non-Abelian band topology in photonic scattering networks

Yuze Hu, Mingyu Tong, Tian Jiang et al. (+10 more)

The concept of multi-gap topology has recently been shown to give rise to uncharted phases beyond conventional single-gap classifications. These phases relate to band nodes with non-Abelian quaternion charges and momentum-space braiding processes characterized by new invariants such as paradigmatic Euler class, phenomena that intrinsically require at least two spatial dimensions. Extending such phases into the non-equilibrium regime is predicted to unlock even richer multi-gap topologies beyond static settings, yet their experimental realization has remained elusive due to the stringent requirements on dimensionality, symmetry, and dynamical control. Here, we theoretically demonstrate and, for the first time, experimentally realize two-dimensional (2D) Floquet non-Abelian band topology in photonic scattering networks. Within this platform, we uncover a sequence of topological phenomena unique to 2D multi-gap systems far from equilibrium, including anomalous multi-gap phases interconnected by band nodes, Floquet Euler transfer, gapped phases with anomalous Dirac string configurations, and Floquet-induced non-Abelian braiding of band nodes. In addition, we observe Floquet-periodic anomalous edge states across multiple gaps, providing experimental signatures of these sought-after 2D multi-gap Floquet topological phases. Our results establish photonic scattering networks as a practical and versatile route to non-Abelian Floquet systems, opening avenues for dynamical topological physics with braiding capability and robust photonic functionalities.
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All authors Yuze Hu, Mingyu Tong, Tian Jiang, Shuxing Yang, Ning Han, Fujia Chen, Li Zhang, Rui Zhao, Qiaolu Chen, Hongsheng Chen, F. Nur Ünal, Robert-Jan Slager, Yihao Yang

Materials Science · Cross-listed from cs.RO

A Soft Robotic Demonstration in the Stratosphere

Codrin Tugui, Tirth Thakar, Anatol Gogoj et al. (+5 more)

Machines designed for operation in Space, as well as other extreme environments, need to be both resilient and adaptable when mission parameters change. Soft robots offer advantages in adaptability, but most lack resilience to the pressure and temperature extremes found as close as the Stratosphere. Dielectric elastomer actuators overcome some of those limitations when built as solid state compliant capacitors capable of converting electrical energy into mechanical work, but the elastomer resilience limits the device's operating window. Here we present a crosslinking mechanism for silicone elastomers under ultraviolet light using trimethyl(methylcyclopentadienyl)platinum(IV) as a catalyst to react hydrosilane to vinyl groups. The formation of carbon-carbon bonds enables fast processing under UV light and exceptional electro-mechanical performance in dielectric elastomer actuators. The material resilience advantage is demonstrated in controlled experiments at -40{\deg} and 120{\deg} C, as well as near vacuum, in comparison with state-of-the-art acrylic and silicone chemistries. Fully autonomous systems controlling grippers made with the novel silicone were integrated into payloads for high altitude balloon testing. Two stratospheric balloon missions were carried out and demonstrated DEAs as a viable soft robotic technology under space-like conditions (as high as 23.6 km elevation, at <0.05 atm and -55{\deg} C). The combinations of chemical building blocks and catalyst can be further expanded to address other challenges for silicones, including adhesion and additive manufacturing.
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All authors Codrin Tugui, Tirth Thakar, Anatol Gogoj, Alexander White, Ang Leo Li, Alexander Yin, Edward Pomianek, Mihai Duduta

Materials Science

Study on the Effect of Annealing on Ga$_2$O$_3$ Thin Films Deposited on Silicon by RF Sputtering

Ana Sofia Sousa, Duarte M. Esteves, Tiago T. Robalo et al. (+3 more)

Gallium oxide is an ultra-wide bandgap semiconductor with excellent opto-electronic properties, making it a highly promising material for a wide range of applications and devices. In this article, we report how the optical, morphological, structural, and compositional properties of $\beta$-Ga$_2$O$_3$ thin films deposited by RF sputtering on silicon substrates are affected by thermal treatments. Ellipsometric spectra recorded at multiple angles of incidence from several samples subjected to thermal annealing in the range of 550-1000 $^\circ$C were analyzed to extract the optical functions using appropriate multilayer models. This analysis is complemented by compositional, structural, and morphological characterization techniques. A significant increase of the refractive index was found after annealing at 1000 $^\circ$C, accompanied by a stark improvement in the samples' crystalline structure, as confirmed by complementary structural and compositional characterization techniques.
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All authors Ana Sofia Sousa, Duarte M. Esteves, Tiago T. Robalo, Mário S. Rodrigues, Katharina Lorenz, Marco Peres

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

Ab initio study of saddle-point excitons in monolayer SnS2

Vinicius Alves Bastos, Fulvio Paleari, Eleonora Luppi et al. (+2 more)

Monolayer SnS2 has emerged as a promising visible-light photocatalyst for photoelectrochemical applications, owing to its strong optical absorption in the visible range and excellent chemical stability. Despite its reduced dimensionality - where excitonic effects are expected to be pronounced - comprehensive theoretical investigations of bound excitons in this material remain scarce. Notably, unlike most two-dimensional hexagonal crystals, monolayer SnS2 exhibits its lowest single-particle transition at the M point of the Brillouin zone (BZ). Here, the electronic valence bands form a saddle point while conduction states display a minimum with pronounced anisotropy, creating a distinctive band topology whose impact on optical excitations has not yet been systematically explored. In this work, we present a first-principles study of bound excitons in monolayer SnS2 based on state-of-the-art many-body perturbation theory, employing the GW approximation and the Bethe-Salpeter equation (BSE). We analyze how band symmetry and anisotropy shape the excitonic wavefunctions and transition dipole moments. By resolving the exciton dipoles in momentum space for different linear light polarizations, we demonstrate that linearly polarized light lifts the C3 rotational symmetry relating the three inequivalent M points, giving rise to three linearly independent excitonic states. This polarization-selective coupling, previously identified for saddle points in graphene, is achieved in SnS2 for bound excitons and provides a potential route toward state encoding schemes in valleytronics applications.
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All authors Vinicius Alves Bastos, Fulvio Paleari, Eleonora Luppi, Marco Gibertini, Alice Ruini

Materials Science

The effect of chemical vapor infiltration process parameters on flexural strength of porous {\alpha}-SiC: A numerical model

Joseph J. Marziale, Jason Sun, Eric A. Walker et al. (+3 more)

The flexural strength variability of {\alpha}-SiC based ceramics at elevated temperatures creates the need for an Integrated Computational Materials Engineering (ICME) framework that relates the strength of a specimen directly to its manufacturing process. To create this ICME framework a model must first be developed which establishes a relationship between the chemical vapor infiltration (CVI) process and parameters, the resulting mesoscale pores, and the overall macroscale flexural strength. Here a nonlinear single pore model of CVI is developed used in conjunction with a four-way coupled themo-mechanical damage model. The individual components of the model are tested and a sample system under a four-point bending test is explored. Results indicate that specimens with an initial porosity greater than 30% require temperatures below 1273 K to maintain structural integrity, while those with initial porosities less than 30% are temperature-independent, allowing for optimization of the CVI processing time without compromising strength.
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All authors Joseph J. Marziale, Jason Sun, Eric A. Walker, Yu Chen, David Salac, James Chen

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

Dimensional reduction by singlet blockade in the distorted kagome magnet YCa$_3$(CrO)$_3$(BO$_3$)$_4$

Umashankar Jena, Satish Kumar, Harald O. Jeschke et al. (+3 more)

The distorted kagome borate YCa$_3$(CrO)$_3$(BO$_3$)$_4$ has a Curie-Weiss temperature of -140 K and shows no magnetic order down to $65$ mK. We determine its Heisenberg Hamiltonian by density-functional energy mapping, obtaining twenty-four symmetry-inequivalent Cr-Cr exchange paths dominated by $J_1=116$ K, and measure the susceptibility, specific heat and ac susceptibility to $50$ mK. The Hamiltonian does not by itself account for the absence of order: simulated classically it orders at $10$ K, a factor of $154$ above the bound. We trace the gap to the site symmetry of the $P6_3$ structure, which divides the exchange network in two: $J_1$ binds two thirds of the Cr into dimers, while the remaining third forms uniform spin-$3/2$ chains along $c$ through a weaker $J_2=33$ K. The chains share no direct bond, and each of the fourteen paths leaving a chain terminates on a spin locked into a dimer singlet of gap $\Delta=J_1$. This singlet blockade demotes the interchain coupling to second order; summed over paths with their relative Néel parity it falls to a few tens of millikelvin, against $9.8$ K at first order, and what survives is frustrated on the kagome lattice the chains themselves form. Treating the dimers exactly and the chains by exact diagonalization accounts, without free parameters, for the position of the magnetic specific-heat maximum and the entropy recovered by $100$ K, but not for the susceptibility, which additionally requires a broad distribution of exchange couplings that we attribute to Ca/Y site mixing. That disorder also impacts the thermodynamics at lowest temperatures: below $0.7$ K the magnetic specific heat follows a field-robust $T^2$ law, which excludes one-dimensional chains with gapless excitations, Goldstone modes and spinons alike and implies a linear density of predominantly non-magnetic states, matched by the singlet-triplet gaps the disorder generates.
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All authors Umashankar Jena, Satish Kumar, Harald O. Jeschke, G. B. G. Stenning, Panchanana Khuntia, Yasir Iqbal

Materials Science

Electronic and structural properties of V$_2$O$_5$ layered polymorphs

Sakthi Kasthurirengan and Hartwin Peelaers

V$_2$O$_5$ is a promising battery electrode material that can intercalate not only Li, but also more abundant alkaline metals such as Na and K, and even multivalent ions such as Al, Ca, Cu, Mg, and Zn. V$_2$O$_5$ exhibits several different polymorphs, and phase transitions between the polymorphs can occur depending on intercalant or external conditions. At least 8 different layered polymorphs have been observed. However, detailed information about the energetics and structural properties of each polymorph is still lacking. To obtain a reliable computational reference, we use hybrid density functional theory calculations to investigate the properties of layered V$_2$O$_5$ polymorphs. We benchmarked several methods to include van der Waals interactions in combination with hybrid functionals, and found that the Grimme D3 method is most accurate. We obtain detailed information on the electronic properties and structures of the various unintercalated polymorphs and show that the main electronic effect of intercalants is a filling of the lowest conduction bands, as the intercalant contributions are well above the conduction-band minimum. Despite the structural differences between the unintercalated polymorphs, we find that they have very similar band gaps and band structures, with the exception of the high temperature and pressure phase $\beta$.
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Materials Science

Chemical Vapor Deposition of Epitaxial Chromium Nitride Thin Films

Lewis J. Adams, Sara Baserga, Laurent Souqui et al. (+3 more)

Chromium nitride (CrN) is a thermoelectric transition metal nitride whose properties are strongly influenced by stoichiometry, substrate choice, and defect chemistry. CrN is routinely synthesized by physical vapor deposition (PVD), its growth by chemical vapor deposition (CVD) has been limited by the lack of suitable chromium precursors capable of producing carbon-, oxygen-, and chlorine-free films. CVD of contamination-free Cr compounds is notoriously difficult, with carbon-free Cr compounds thought unattainable below 1000 C. Here, we report epitaxial, carbon- and chlorine-free CrN thin films synthesized by thermal CVD. Single-phase CrN films (~110 nm) were deposited on c-plane alpha-Al2O3 using in-situ generated chromium chlorides. Films exhibit n-type conduction with a Seebeck coefficient of -36 uV/K, comparable to PVD-grown CrN. These results present a routeto highly crystalline rock-salt CrN films for defect engineering, doping, and alloying with reduced implantation-related damage capabilities previously largely confined to PVD-based techniques.
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All authors Lewis J. Adams, Sara Baserga, Laurent Souqui, Enji Sadek, Linus von Fieandt, Per Eklund

Materials Science

Machine-learned interatomic potential for titanium carbide MXenes: Application to ion irradiation simulations

Jesper Byggmästar

A computationally efficient and accurate machine-learned (ML) interatomic potential is developed for bare Ti$_{n+1}$C$_n$ MXenes. With a diverse set of structures computed with density functional theory, the trained ML potential demonstrates good accuracy and robustness to a wide range of bond distances and environments, making it a useful tool for molecular dynamics simulations of MXenes subjected to mechanical load or irradiation. The ML potential is applied to simulations of light and heavy ion irradiation, gathering insight into the statistics and probabilities of sputtering, reflection, defect creation, and implantation into bare Ti$_{n+1}$C$_n$ MXene sheets. The results provide guidelines for defect engineering of MXenes through ion irradiation and implantation. Additionally, the ML potential development provides a landmark recipe for enabling machine-learning-driven atomistic simulations of other MXenes.
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Materials Science

Nine-element machine-learned interatomic potentials for multiphase refractory alloys

Jesper Byggmästar, Tiago Lopes, Zheyong Fan et al. (+1 more)

New refractory alloys are being continuously designed and characterised for applications requiring good high-temperature mechanical properties and stability. Computational design from atomistic simulations is limited by interatomic potentials missing key elements, being too inaccurate, or computationally too slow for large-scale simulations. Here we present development of a refractory alloy database and two computationally efficient and general-purpose machine-learned potentials (tabGAP and NEP). We also design a cross-sampling strategy for effective sampling of training data using predictions from two potentials with completely different underlying architecture. The potentials support arbitrary alloy compositions of elements in groups four to six in the periodic table (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W). The database is diverse yet multitargeted to enable simulations of refractory metals and alloys across different pure-metal, solid-solution, intermetallic, and glassy phases. We demonstrate the usefulness of the potentials by reproducing known pressure-, temperature-, and solute-induced phase transitions, grain boundary segregation, and simulations of radiation damage in the WTaCrVHf metallic glass.
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All authors Jesper Byggmästar, Tiago Lopes, Zheyong Fan, Tapio Ala-Nissila

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

Quantum oscillations and linear magnetoresistance in ultraclean CaVO$_3$ thin films

M. Müller, M. Espinosa, O. Chiatti et al. (+3 more)

Advances in epitaxy of transition metal oxides with perovskite structure allow novel insights into transport mechanisms of strongly correlated electron systems, which are of interest for future transparent electronics. In this study, we investigate magnetotransport properties of thin epitaxial CaVO$_3$ films, grown coherently strained on LaAlO$_3$, and demonstrate for the ultraclean limit quantum oscillations. Fermi liquid behavior is detected in the temperature-dependent resistivity $\rho(T) \sim T^2$ up to 20 K, with effective mean free paths exceeding up to 20 times the film thickness (38 nm). Shubnikov-de Haas oscillations and a non-linear Hall resistance reveal two electron-like (1 and 2) and one hole-like (h) carriers, reflecting the three-fold Fermi surface of orthorhombic CaVO$_3$, with effective charge carrier densities and mobilities at 4.2 K of: (1) $n_1 \approx 9.3 \cdot 10^{21}{}cm^{-3}$ with low mobility $\mu_1 \approx 926{}cm^{2}V^{-1}s^{-1}$, (2) $n_2 \approx 7.2 \cdot 10^{19}{}cm^{-3}$ with high mobility $\mu_2 \approx 6600 {}cm^{2}V^{-1}s^{-1}$, and (h) $n_h \approx 2.2 \cdot 10^{18}{}cm^{-3}$ with $\mu_h \approx 1500{}cm^{2}V^{-1}s^{-1}$. A non-saturating linear magnetoresistance dominates at low temperatures, exceeding the value for single crystals by 30$\%$. Our findings on epitaxial films demonstrate the delicate interplay of multiple carriers with correlations stemming from a non-spherical nested Fermi surface of a perovskite structure with orthorhombic distortion.
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All authors M. Müller, M. Espinosa, O. Chiatti, T. Kuznetsova, R. Engel-Herbert, S. F. Fischer