Materials Science · Cross-listed from physics.optics
Phase-Transition-Driven Hyperbolic Optical Response and Directional Polaritons in Epitaxial VO2 Thin Films
Maria Chiara Paolozzi, Annalisa D Arco, Ilaria Martinelli et al. (+10 more)
Optical anisotropy in crystalline solids enables direction-dependent light-matter interactions and underpins a variety of advanced photonic functionalities. In this context, Vanadium dioxide (VO2) represents a prototypical material that undergoes a reversible MIT near 67{\deg}C, accompanied by pronounced electronic, structural, and optical modifications. The MIT not only dramatically modifies the VO2 electrical conductivity but also reshapes its anisotropic optical response, making VO2 an exceptional platform for dynamically tunable photonic and optoelectronic devices. In this work, we investigate how the intrinsic crystalline anisotropy of VO2 induces a
hyperbolic optical behavior in the metallic rutile phase. We study two epitaxial VO2 thin films of different thicknesses grown on (110) oriented MgF2 substrates. Broadband polarized spectroscopic measurements, spanning the infrared to UV spectral range, are employed to independently investigate the optical response in both the monoclinic and rutile phases. From these measurements, we extract the optical conductivity and the dielectric function, revealing a pronounced anisotropy in the rutile metallic phase, with an enhanced free-carrier response along the rutile c axis. Our data show that, within a narrow near-infrared spectral window, the real parts of the dielectric tensor components along the two principal axes acquire opposite signs, indicating the emergence of a
hyperbolic type-II dispersion. The
hyperbolic response is quantitatively evaluated through the quality factor and the degree of dielectric anisotropy, enabling a systematic assessment of VO2 as a thermally switchable,
hyperbolic optical medium. These findings expand the understanding of anisotropy-driven optical phenomena in phase-change materials and highlight VO2 thin films as a promising platform for tunable and reconfigurable photonic applications.
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All authors Maria Chiara Paolozzi, Annalisa D Arco, Ilaria Martinelli, Lorenzo Mosesso, Jacopo Sera, Alessandro D Elia, Augusto Marcelli, Yingxue Chen, Chongwen Zou, Maria Cristina Larciprete, Marco Centini, Stefano Lupi, Salvatore Macis
Materials Science
Thin film synthesis of SrZn2P2 with SrI2 post-annealing for enhanced crystallinity and optoelectronic quality
Sita Dugu, Shaham Quadir, Christopher P. Muzzillo et al. (+11 more)
Ternary Zintl phosphides are promising light-absorbing
semiconductors for thin-film optoelectronic applications, but strategies for controlling their microstructure and optoelectronic quality remain underexplored. Here, we report the synthesis of phase-pure SrZn2P2 thin films using
radio-frequency co-sputtering in a PH3 + Ar atmosphere and investigate the impact of post-growth processing on their structural and optical properties. Grazing-incidence X-ray scattering and Raman spectroscopy confirm the formation of crystalline SrZn2P2 films over a finite compositional window. Optical measurements reveal strong absorption near the direct-band-gap energy (~1.8 eV) and near-band-edge photoluminescence. Further, we have studied the effects of chemically compatible halide-assisted annealing. It is found that SrI2 treatments lead to pronounced grain growth and reduced diffraction peak broadening while preserving phase purity, in contrast to rapid thermal or forming-gas annealing. Notably, annealing with SrI2 at 450 {\deg}C significantly enhances both the intensity and spatial uniformity of the photoluminescence, thus connecting the observed microstructural consolidation with improved radiative recombination. Our study demonstrates that halide-assisted annealing provides an effective pathway for microstructural control in SrZn2P2 thin films and highlights a generalizable processing strategy for advancing Zintl phosphide
semiconductors toward optoelectronic applications.
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All authors Sita Dugu, Shaham Quadir, Christopher P. Muzzillo, Zhenkun Yuan, Smitakshi Goswami, Xiaojing Hao, Jialiang Huang, Guillermo Esparza, Baptiste Julien, David Fenning, Jifeng Liu, Geoffroy Hautier, Andriy Zakutayev, Sage R. Bauers
Materials Science
Resolving growth-induced off-stoichiometry in AgCrSe$_2$ single crystals
Felix Eder, Zeno Maesen, Yurii Skourski et al. (+3 more)
The layered delafossite-like antiferromagnet AgCrSe$_2$ is a superionic conductor at high temperatures and has been reported to exhibit anomalous
Hall behavior and Kondo physics at low temperatures. These extraordinary transport properties have been established almost exclusively on single
crystals grown by chemical vapor transport, raising questions about the role of growth-induced off-stoichiometry. Using elemental analysis, single-
crystal X-ray diffraction, and magnetization measurements, we show that such
crystals are indeed systematically off-stoichiometric, with a general composition of Ag$_{1-x}$Cr(Se$_{2-y}$Cl$_y$) ($x \approx y \approx 0.08$) arising from the use of CrCl$_3$ as a transport
agent. This off-stoichiometry manifests in altered
magnetic properties, most notably a suppressed Néel temperature of 46\,K compared to 58\,K in stoichiometric polycrystalline samples prepared by solid-state synthesis. By optimizing an Ag/Se self-flux growth method, we obtained large single
crystals of AgCrSe$_2$ that recover the
magnetic transition temperature and saturation field of stoichiometric powder samples. These results establish self-flux growth as a route to high-quality stoichiometric AgCrSe$_2$ single
crystals and provide a reliable platform for reassessing whether the reported anomalous transport phenomena are intrinsic or arise from off-stoichiometry.
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All authors Felix Eder, Zeno Maesen, Yurii Skourski, Enrico Giannini, Oksana Zaharko, Fabian O. von Rohr
Materials Science · Cross-listed from physics.bio-ph
Can we teach generative artificial intelligence the design language of engineered living materials?
Andrés Díaz Lantada, José A. Yáñez, William Solórzano-Requejo et al. (+1 more)
This study presents a versatile ontology and a useful codification scheme for describing all kinds of engineered living materials (ELMs). The different components of the ontology, namely: families according to the taxonomy for ELMs, industrial applications and synthesis or processing methods, are systematically organized, enumerated, classified, codified and explained. The methodic application of the ontology to a set of 100 relevant examples of ELMs helps to demonstrate its utility and adaptability to many different types of ELMs with a wide range of industrial applications and obtained through numerous synthesis and processing methods. This proves that the developed ontology and codification schemes, with the glossary provided to support its implementation and application, can serve as a comprehensive classification tool for the emergent field of ELMs. Furthermore, the usability of the ELMs ontology and codification by a generative artificial intelligence (AI) is explored and validated by different means, checking that both natural
language and the codification are understandable for describing ELMs, verifying that the generative AI adequately codifies examples of ELMs according to the ontology, and validating the synergic applicability of the ontology and codification with generative AI tools for illustrating novel ELMs and supporting their conceptual design. This study is expected to provide a universal
language to facilitate communication in the ELMs field and to foster the discovery of new ELMs and related innovations, hoping it may accelerate scientific and technological discoveries.
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All authors Andrés Díaz Lantada, José A. Yáñez, William Solórzano-Requejo, Monsur Islam
Materials Science
Tracking visible pulsed laser annealing of Hf$_{0.5}$Zr$_{0.5}$O$_2$ heterostructures with in situ transmission electron microscopy
Aida Amini, Shruti Verma, Katharina Kohlmann et al. (+4 more)
Laser annealing offers a promising route to back end of the line fabrication of ferroelectric thin film transistors based on hafnium-zirconium
oxide (HZO). Due to the wide band gap of this material, previous reports have studied the crystallization of HZO using ultraviolet or infrared light. In contrast, we monitor its crystallization in a Si$_3$N$_4$/TiN/Hf$_{0.5}$Zr$_{0.5}$O$_2$ thin film
heterostructure upon irradiation with visible nanosecond
laser pulses. This geometry mimics the structure of CMOS devices and harnesses the absorption of TiN in the visible regime to generate the heat necessary for the transformation. Through a series of local in situ measurements using a modified transmission electron microscope, we quantify the relationship between the HZO film thickness, critical
laser energy density and the ferroelectric HZO phase fraction, finding a sharp threshold behavior in the
laser pulse energy necessary to crystallize HZO. The optimal condition of irradiating an 8-nm HZO film with a single
laser pulse with an energy density of 177 mJ/cm$^2$ is found to produce 86% of the ferroelectric orthorhombic phase. Heat transfer dynamics within the
heterostructure during
laser annealing are revealed by finite element simulations, where the partial melting of the silicon nitride substrate is found to play an important role limiting the temperature to 1900 {\deg}C. This finding as well as the observed
laser pulse energy threshold behavior support a kinetic crystallization pathway involving the tetragonal phase. More generally, these findings show how
laser-driven phase engineering can lead to scalable design and enhanced performance of ferroelectric materials in advanced electronic applications.
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All authors Aida Amini, Shruti Verma, Katharina Kohlmann, Sebastian Obernberger, Jean-Christof Lamanque, Andreas Rüdiger, Kenneth R. Beyerlein
Materials Science · Cross-listed from cond-mat.mes-hall
Non-Equilibrium Orbital Transport in Terahertz Optorbitronics
Sobhan Subhra Mishra and Ranjan Singh
Modern information technologies rely on controlling the flow of electrons through their charge and
spin. A rapidly emerging alternative is to use the orbital motion of electrons, the way they circulate around atomic sites as a new carrier of information. This orbital angular momentum (OAM) could enable more energy-efficient devices and reduce reliance on scarce heavy elements, but how orbital currents are generated and transported, especially on ultrafast timescales, remains largely unknown. In this review, we introduce terahertz optorbitronics, an approach that uses ultrafast femtosecond
laser pulses and terahertz radiation to observe orbital transport in real time. On timescales of quadrillionth of a second, this technique allows us to track how orbital currents are launched, propagate, and convert into electrical signals in nanoscale thin-film materials. Surprisingly, recent experiments have revealed conflicting pictures such as orbital currents may travel over tens of nanometres like ballistic waves or instead decay within just a few atomic layers, highlighting a fundamental unresolved question in the field. We explain how these ultrafast measurements can disentangle orbital motion from conventional
spin transport, and we highlight new materials from engineered
graphene to altermagnets, that could act as tunable sources of orbital currents. We also discuss how light, electrical gating, strain, and interface design can be used to actively control orbital transport and improve its conversion into usable electronic signals. By revealing orbital transport as a dynamic, non-
equilibrium process, terahertz optorbitronics opens a new direction for nanoscale science, the one that could lead to faster, more efficient technologies operating beyond the limits of conventional
spin-based electronics.
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Materials Science
Discovering physical mechanisms from experiment-simulation mismatches
Yue Li, Penghui Yang, Yushan Xiao et al. (+7 more)
Scientific discovery often begins where observation and prediction disagree. As computation and machine learning survey chemical space, experiment-simulation mismatches are exposed at scale, while tracing them to physical mechanisms remains expert-led. Here we present eXplainable DFT (XDFT), a self-evolving
agent that turns this process into an executable search. XDFT formalizes candidate mechanisms as executable hypotheses, adjudicates their consequences against experiment and distils trajectories into priors for later searches. This couples a solving loop from mismatch to mechanism with a learning loop through which solving changes the solver. Across 112 source-audited cases in which standard calculations predict a metal whereas experiments find a
semiconductor, XDFT resolved 105 with evidence-supported mechanisms within a single-GPU envelope. After 60 cases, the resolving mechanism ranked among the first three hypotheses for 80% of held-out cases, up from 7% under the initial expert prior. XDFT also returned evidence-graded mechanisms for seven expert-curated questions about physical mechanisms. These results establish experiment-simulation mismatches as tractable starting points for scientific
agents that discover physical mechanisms while learning how to find the next.
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All authors Yue Li, Penghui Yang, Yushan Xiao, Zhonghan Zhang, Jianguo Huang, Yuhao Lu, Cuntai Guan, Bo An, Bijun Tang, Zheng Liu
Materials Science
Predicting massive helium-3 release from metal tritides using simple mechanical modeling
Berengere Evin, Dorian Gaboriau, Mathieu Segard et al. (+3 more)
This letter is presenting a simple but effective mechanism that explains why ,during tritium aging, metal tritides retain most helium-3 for years and then suddenly release massive amount. The mechanism is based on the hypothesis that dislocations blocking could explain the sudden change of behavior. The modeling of this phenomenon combine a mechanical and microstructural approach. The calculations made with this mechanism fit all the aging data acquired on aged palladium tritide
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All authors Berengere Evin, Dorian Gaboriau, Mathieu Segard, Sylvain Challet, Arnaud Fabre, Stephanie Thiebaut
Materials Science
Emergent surface resonance from charge density wave symmetry breaking in TiSe2
Turgut Yilmaz, Yi Sheng Ng, Muhammad Awais Fiaz et al. (+13 more)
Surface confined electronic states provide a fertile ground for discovering emergent phenomena that have no counterpart in the bulk, offering new routes to manipulate correlations,
symmetry breaking, and dimensionality at the atomic scale. Here, we show that charge density wave (CDW)
symmetry breaking can yield a surface states in 1T-TiSe2. Micro angle resolved photoemission spectroscopy resolves a sharp, two dimensional surface resonant state (SRS) that emerges within the CDW reconstructed low energy spectrum. The SRS exhibits notable temperature dependence and its spectral weight collapses around 160 K, while CDW transition temperature TCDW is commonly reported as 202 K. Slab DFT+U calculations reproduce a surface localized resonance when CDW folding brings valence and conduction states into near degeneracy, suggesting a correlation tuned, surface selective origin. These results point to a form of correlation-tuned surface resonance in a layered CDW compound and suggest a framework for engineering low dimensional
quantum states in van der Waals materials via
symmetry breaking and electronic structure tuning.
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All authors Turgut Yilmaz, Yi Sheng Ng, Muhammad Awais Fiaz, Anil Rajapitamahuni, Asish K. Kundu, Shawna M. Hollen, Polina M. Sheverdyaeva, Paolo Moras, Ivana Vobornik, Jun Fujii, Shinichiro Ideta, Kenya Shimada, Boris Sinkovic, Elio Vescovo, Hui-Qiong Wang, Jin-Cheng Zheng
Materials Science · Cross-listed from cond-mat.mes-hall
Beyond conventional skyrmions in synthetic antiferromagnets
Kayla Fallon, Reshma Peremadathil-Pradeep, Christopher E. A. Barker et al. (+14 more)
Magnetic skyrmions are topologically protected
spin textures that can act as reconfigurable nanoscale information carriers. In synthetic antiferromagnets (SAFs), interlayer exchange coupling offers an additional control parameter beyond the interfacial Dzyaloshinskii-Moriya interaction (DMI) and
magnetic anisotropy. Here, we engineer a SAF composed of two chemically distinct ferromagnets (CoB and CoFeB), in which the external
magnetic field and interlayer exchange act asymmetrically on the sublattices. The competition of these effects, acting as a resultant effective-field, gives rise to two distinct skyrmion families in different field regimes. In large fields, conventional-polarity skyrmions nucleate, with core antiparallel to the external field, whereas in smaller fields an inverse-polarity skyrmion state emerges as the effective-field reverses sign and almost saturates the CoFeB layers. Return-point
memory measurements confirm independent nucleation pathways for the two families. Using element-resolved x-ray magnetometry, correlative
magnetic force and Lorentz transmission electron microscopies, and parameter-matched micromagnetic modelling, we show that all textures reside only in the CoFeB layers, which experience a Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange field originating from the CoB layers. This effective-field method provides a robust route to programmable three-dimensional
spin textures with controlled polarity in selected layers of a multilayer with potential for applications in skyrmion-based computing and
spin-logic architectures.
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All authors Kayla Fallon, Reshma Peremadathil-Pradeep, Christopher E. A. Barker, Zoey Tumbleson, Emily Darwin, Andrea Meo, Eloi Haltz, Benjamin A. Brereton, Trevor Almeida, Colin Kirkbride, Sara Villa, Sophie A. Morley, Mario Carpentieri, Riccardo Tomasello, Hans J. Hug, Christopher H. Marrows, Stephen McVitie
Materials Science
Third-order intrinsic anomalous Hall effect as a transport fingerprint of altermagnets
Longjun Xiang, Hao Jin and Jian Wang
The intrinsic anomalous
Hall effect (IAHE) provides a powerful transport fingerprint of
quantum magnets, with its linear and second-order responses distinguishing ferromagnets and $\mathcal{P}\mathcal{T}$-symmetric antiferromagnets, respectively. Altermagnets, as an emergent class of
quantum magnets, have recently been shown to host a third-order extrinsic anomalous
Hall effect, raising a question of whether an intrinsic counterpart can serve as a diagnostic of altermagnetic order. Based on
spin-group
symmetry analysis, we demonstrate that the third-order IAHE is generically allowed in the ten
spin Laue groups relevant to altermagnets when
spin-orbit coupling (SOC) is taken into account. By combining these
symmetry constraints with the anomalous velocity induced by the second-order Berry
curvature, we uncover a resonant third-order IAHE arising near the altermagnetic band crossings at generic momenta in both the Lieb-
lattice altermagnet and the experimentally realized altermagnet V$_2$Se$_2$O. Notably, we identify the Berry
curvature quadrupole, encoded in the second-order Berry
curvature and activated by finite SOC, as the microscopic
quantum geometric origin of this resonance. Our results establish the third-order IAHE as an intrinsic
quantum geometric transport fingerprint of altermagnets and extend the hierarchy of IAHE across collinear
quantum magnets.
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Materials Science
Revealing magnetism in the distorted kagome $R$Ti$_3$Bi$_4$ ($R$ = Nd, Sm, Gd) via ARPES and XMCD
C. Lim, F. Ballester, A. Kar et al. (+19 more)
Kagome materials are known for hosting emergent
quantum phenomena driven by the interaction between different
lattice, charge and
spin orders. Here, we present a detailed angle resolved photoemission (ARPES), density functional theory (DFT) and x-ray
magnetic circular dichroism (XMCD) study of the electronic and
magnetic structure of $R$Ti$_3$Bi$_4$ ($R$ = Nd, Sm, Gd). ARPES and DFT demonstrate that the bulk electronic band structure is dominated by the hybridization of the Ti bands, and the weak electron-like pocket at $\Gamma$ is identified as a surface state. The isotropic XAS profile of the $M_{4,5}$-edge of the rare earth is consistent with the presence of $R^{3+}$ oxidation state. Using the XMCD sum rules, backed by the atomic multiplet theory calculations, we obtain the
spin and orbital
magnetic moments. The Ti $L_{2,3}$-edge XMCD reveals the presence of a small
magnetic moment in GdTi$_3$Bi$_4$, presumably driven by the proximity of the {Ti} kagome layers to the $zigzag$ chains of Gd, while the total
magnetic moment of Gd is shared by the $f$ and $d$ electrons. Our combined XMCD, ARPES and DFT study brings an important piece of information to understand the
spin flip transitions and anomalous
Hall effect observed in the $R$Ti$_3$Bi$_4$ kagome metals.
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All authors C. Lim, F. Ballester, A. Kar, M. Alkorta, D. Subires, J. Dai, M. Tallarida, E. Vescovo, T. K. Kim, C. Cacho, C. Yi, S. Roychowdhury, A. Kumar Sharma, Y. Choi, G. Fabbris, J. Strempfer, P. Gargiani, C. Shekhar, C. Felser, I. Errea, M. G. Vergniory, S. Blanco-Canosa
Materials Science
Unraveling the symmetry of Al5C3N
Vitalii Shtender, Chin Shen Ong, Pedro Berastegui et al. (+6 more)
The high-temperature ceramic compound Al5C3N with promising application usage belongs to the scarcely studied Al-C-N system. It was originally reported as an ordered compound in the non-centrosymmetric space group P63mc and described as a nanolaminate with an -Al2C-AlN-Al2C2- stacking sequence. The recently reported structural disorder in the related compound Al4SiC4 led us to question this proposed structure for Al5C3N and investigate the possibility of a disordered structure in the centrosymmetric space group P63/mmc. In the present work, we employed different synthesis routes to maximize the yield and quality of the desired phase, and applied a variety of techniques to probe the Al5C3N
crystal structure. Our single-
crystal X-ray diffraction analysis clearly indicates that the non-centrosymmetric space group P63mc must be rejected. From a joint refinement of single-
crystal X-ray and powder
neutron diffraction data, the occupancies of C and N were refined at two sites in P63/mmc resulting in the stacking sequence -Al2C-Al(C/N)-Al2(C/N)2-. Furthermore, DFT calculations show that a centrosymmetric disordered structure described in a supercell has the lowest energy, 0.2 eV per formula unit, relative to the previously reported P63mc structure. The calculated band structure shows both direct and indirect band gaps which lead to implications for the physical properties. Finally, STEM analysis provides additional evidence that the
crystal structure of Al5C3N is better described in the centrosymmetric space group P63/mmc.
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All authors Vitalii Shtender, Chin Shen Ong, Pedro Berastegui, Olivier Donzel-Gargand, Johan Cedervall, Charles Hervoches, Premek Beran, Olle Eriksson, Ulf Jansson
Materials Science
AIM2DAT: A Python-based Automated Ab Initio Material Modeling and Data Analysis Toolkit
Holger-Dietrich Saßnick, Joshua Edzards, Timo Reents et al. (+1 more)
The emergence of data-driven computational materials science offers unprecedented opportunities to explore complex material landscapes, complementing experimental research with the discovery of novel compounds. To enable these developments, it is essential to establish robust, reliable, and easy-to-use software supporting workflow automation and large
dataset processing. Herein, we introduce the Automated Ab Initio Materials Modeling and Data Analysis Toolkit (aim2dat), a Python package offering a user-friendly interface to generate and handle big data, design high-throughput workflows based on density functional theory calculations, and analyze the output. Its key features include interfaces to online databases for structure query and analysis, high-throughput screening routines, and seamless integration of machine learning models. The capabilities of aim2dat are showcased with a variety of use-cases, ranging from photocathode materials to metal-organic frameworks.
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All authors Holger-Dietrich Saßnick, Joshua Edzards, Timo Reents, Caterina Cocchi
Materials Science · Cross-listed from physics.chem-ph
Physics-based modeling of cyclic and calendar aging of LIBs with Si-Gr composite anodes
Micha C. J. Philipp, Lukas Köbbing, Alexander Karger et al. (+3 more)
Higher energy density and longer lifetime are the requirements for next-generation lithium-ion batteries. A promising anode material is silicon, which offers high specific capacity, but its significant volume change during lithiation and delithiation enormously reduces battery lifetime. A physical understanding of the processes degrading the battery is key to mitigate this effect and advance in the field. We develop a physics-based model to describe degradation during battery cycling under various protocols and storage conditions, with varying check-up (CU) frequencies. The model can disentangle basic degradation mechanisms, such as the growth of the Solid-Electrolyte Interphase (SEI), from silicon mechanisms, such as particle cracking, SEI growth on cracks, and loss of active material (LAM). We investigate the impact of CUs on the observed storage degradation and the reason behind the increased degradation in batteries, including silicon in the anode. Additionally, we relate the observed degradation to operating conditions, enabling future optimization of battery use and design.
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All authors Micha C. J. Philipp, Lukas Köbbing, Alexander Karger, Andreas Jossen, Arnulf Latz, Birger Horstmann
Materials Science
Anomalous, pre-yield grain-boundary sliding in copper revealed with in-situ high-resolution strain mapping
Benjamin Poole, David Lunt, Luke Hewitt et al. (+1 more)
Grain boundary sliding is typically associated with high temperature deformation in engineering
alloys. Here, we examine grain boundary sliding at room temperature in oxygen-free high-conductivity copper under quasi-static tensile testing. By using high-resolution digital image correlation (HRDIC) conducted in-situ within a scanning electron microscope to produce time-series strain maps, we unexpectedly observe that grain boundary sliding occurs extensively prior to macroscopic yield, and before the onset of significant crystallographic slip. Extreme values in strain and in-plane rotation are found to be associated with grain boundaries immediately prior to yield and during the initial stages of plastic deformation, which are higher than those associated with crystallographic slip. By combining
laser scanning confocal microscopy height mapping with the strain maps and orientation maps from electron backscatter diffraction, grain boundary sliding character is determined, finding evidence of pure in-plane, pure out-of-plane and mixed-mode sliding.
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All authors Benjamin Poole, David Lunt, Luke Hewitt, Chris Hardie
Materials Science
Geometry-Based Neural-Network Prediction of Electron Localization Function Topology in Dense Hydrogen
Xiaoyu Wang, Miriam Marqués, Sergio Gómez et al. (+3 more)
We develop a machine-learning framework to predict the electron localization function (ELF) of pure, dense hydrogen directly from atomic geometry, bypassing explicit electronic-structure calculations. Trained on first-principles data spanning multiple pressure regimes in dense fluid hydrogen, the model achieves high accuracy ($R^2 > 0.99$) and faithfully reproduces the global distribution of the ELF. A combined real- and reciprocal-space analysis reveals that the residual error is dominated by smooth, long-wavelength components with correlation lengths exceeding typical H–H bonding scales, and that the magnitude of these components increases systematically with pressure. Despite being trained exclusively on dense fluid hydrogen networks, the model transfers robustly to crystalline hydrogen configurations, preserving key features of ELF
topology, including critical points and hydrogen-network connectivity. Taken together, these results suggest a viable route toward geometry-based, high-throughput evaluation of hydrogen-networking characteristics in both fluid and crystalline hydrogen.
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All authors Xiaoyu Wang, Miriam Marqués, Sergio Gómez, Francesc Serratosa, Eva Zurek, Julia Contreras-García
Materials Science
A Theoretical Investigation of the Thermal and Photochemical Mechanisms of Ethylbenzene Dehydrogenation on Rutile TiO$_{2}$(110)
Nico Yannik Merkt
This master's thesis investigates the thermal and photochemical dehydrogenation of ethylbenzene (EB) to styrene on the rutile TiO$_{2}$(110) surface. A dual-methodological
quantum chemical approach is used for this investigation. While industrial styrene production is energy-intensive, photocatalysis on
semiconductor materials offers a promising alternative under significantly milder conditions. To elucidate the underlying mechanisms, this study employs density functional theory (DFT-PBE-D3) for geometry optimization and high-level multi-reference methods (SA-CASSCF) to accurately describe the electronic complexity of excited states and radical intermediates. The investigation reveals that, on the stoichiometric surface, both thermal and photochemical pathways are dominated by
proton-coupled electron transfer (PCET). The wavelength dependence observed in the literature is explained by how the system navigates electronic
manifolds. 343 nm irradiation leads to rapid relaxation into the ground state, where high kinetic barriers persist. In contrast, 257 nm excitation enables the system to persist in higher excited states (S1/T2). This allows the reaction to bypass the rate-determining ground-state barrier. Furthermore, the study demonstrates that surface oxidation causes a fundamental mechanistic shift. On oxidized surfaces, pre-adsorbed oxygen radicals (O$_{Ti}$) enable direct hydrogen atom transfer (HAT), which is more efficient than PCET on reduced surfaces. This "hydrogen scavenger" effect explains the significant increase in styrene yield. This work underscores the necessity of multi-reference treatments for complex surface reactions and provides a fundamental understanding of how surface stoichiometry and
photon energy govern photocatalytic efficiency.
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Materials Science
Polaron Conductivity in $\alpha$-Fe2O3 Quenched by Adsorbed NO2
Tushar K. Ghosh, Elvar Ö. Jónsson, Stephan Steinhauer et al. (+2 more)
Polaron-mediated charge transport in {\alpha}-Fe2O3 plays a central role in its performance as a gas-sensing material, yet the atomistic interaction between surface adsorbates and polarons remains insufficiently understood. Here, density functional theory with Hubbard-U correction (DFT+U) combined with nudged elastic band calculations is used to investigate polaron formation, migration, and quenching at the Fe-terminated {\alpha}-Fe2O3 (0001) surface. The calculated activation energy for small-polaron hopping in bulk {\alpha}-Fe2O3 is found to be 0.12 eV, in excellent agreement with experimental measurements, confirming the validity of the computational approach. Slab calculations show that migration of the polaron from bulk to the surface lowers the energy by 0.12 eV, indicating preferential localization of charge carriers at the gas-solid interface. Adsorption of NO2 induces substantial electron transfer (0.72 e-) from the
oxide to the molecule, eliminating the localized Fe2+ polaron state and thereby suppressing polaronic conductivity. These results provide a direct microscopic explanation for the resistance increase of hematite-based sensors upon exposure to oxidizing gases. More broadly, the study establishes how surface adsorption can modulate charge transport {\alpha}-Fe2O3 through control of polaron populations, offering design principles for improved iron
oxide gas sensors.
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All authors Tushar K. Ghosh, Elvar Ö. Jónsson, Stephan Steinhauer, Panagiotis Grammatikopoulos, Hannes Jónsson
Materials Science · Cross-listed from cond-mat.soft
A Category-Theoretic Framework from Biological Mechanics to Engineered Stimulus-Response Systems
Lee Marom, Skylar Tibbits, Gioele Zardini et al. (+1 more)
Natural materials achieve adaptive behavior through hierarchical organization and coupled mechanisms across scales. Their translation into engineering, however, remains largely heuristic. What is missing is a formal translation framework that carries biological design logic into engineered realization while preserving physical consistency across levels of abstraction. Here we present a category theoretic compositional framework for verified nature-derived design. The framework defines a category of stimulus response dynamical systems with natural and artificial subcategories. It introduces a structure preserving implementation functor from biological mechanics to engineered systems. It also formalizes a machine agnostic specification layer that links behavioral intent to executable fabrication programs. We instantiate the framework on the hygromorphic pinecone hierarchy as a representative biological case. We implement the full pipeline in Grasshopper, where formal specifications are translated into modular parametric scripts that preserve the compositional structure of the model. The resulting designs are fabricated by fused filament fabrication, evaluated experimentally, and tested against model predictions derived from the pipeline. The current implementation generates four actuator classes spanning two stimulus types and two kinematic responses. One actuator arises purely through composition from previously validated components, without additional manual derivation. The results show that compositionality can function not just as a descriptive
language, but as a generative and system level verifiable method for mechanical material design. More broadly, the work provides a concrete route for
embedding formal multiscale
reasoning within increasingly computational, generative, and physics-driven design workflows.
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All authors Lee Marom, Skylar Tibbits, Gioele Zardini, Markus J. Buehler
Materials Science
Molecular Dynamics simulations of Al-Ti metallic alloy melts using a transferable machine-learning potential
Yuna Kato, Jürgen Brillo, Dirk Holland-Moritz et al. (+4 more)
We investigate the structural and dynamical properties of binary aluminum-titanium
liquid metallic
alloys, as a function of temperature and composition. We make use of MD-simulations, using a transferable machine-learning potential developed by Song et al. [Nature Communications 15, 10208 (2024)], and compare our results to experimental data. Although this potential was initially trained on solid properties, we find good agreement between the experimental data and the simulation results for the
liquid state. The excess volume and compositional changes of the structure are captured well by the machine-learned potential. The simulation allows to disentangle local packing from chemical-ordering effects; the latter are found to be weak in Al-Ti. Dynamical quantities like the viscosity and the
diffusion coefficients are also discussed.
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All authors Yuna Kato, Jürgen Brillo, Dirk Holland-Moritz, Fan Yang, Thomas C. Hansen, Thomas Voigtmann, Linnea Heitmeier
Materials Science · Cross-listed from nlin.PS
Turing patterns on non-fluctuating surfaces under mechanical stresses
Fumitake Kato, Hiroshi Koibuchi, Madoka Nakayama et al. (+2 more)
This paper presents a numerical study of Turing patterns (TPs) governed by reaction
diffusion equations for the activator $u$ and the inhibitor $v$ on two- and three-dimensional
lattices without vertex fluctuations. In this framework, $u$ and $v$ are fixed at discrete spatial locations, as pigment
cells on zebrafish skin or shell patterns. Mechanical effects are incorporated through the Finsler geometry modeling formulation, which introduces an internal degree of freedom, $\vec{\tau}$, representing the direction of mechanical stress. A tensile-stress formula based on the Gaussian bond potential is shown to be well defined on non-fluctuating
lattices, enabling the
entropy associated with stress relaxation to be evaluated in a manner analogous to that on fluctuating surfaces. The results indicate that biological TPs respond to external mechanical forces in much the same way as TPs on fluctuating membranes. Simulation codes are provided in the Supplementary Material.
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All authors Fumitake Kato, Hiroshi Koibuchi, Madoka Nakayama, Sohei Tasaki, Tetsuya Uchimoto
Materials Science · Cross-listed from cond-mat.mes-hall
Strain and Twist Engineering of Interfacial Thermal Transport in Homo- and Hetero-Interfaces of Graphene and Hexagonal Boron Nitride
Wenwu Jiang, Huasong Qin, Yilun Liu et al. (+3 more)
A dramatic difference between the vertical thermal conductance response of homogeneous and heterogeneous
graphene/h-BN interfaces to external mechanical perturbations, is predicted. Homogeneous
graphene and h-BN interfaces exhibit strong conductance reduction for both in-plane strain and interfacial twist. Conversely, the vertical thermal conductance of the heterogeneous
graphene/h-BN junction is insensitive to twist deformations but shows significant increase or decrease under compressive or tensile strains, respectively. Our atomistic simulations predictions are rationalized by
Fermi's golden rule and density of
phonon modes analyses, indicating that vertical
phonons and local stacking configurations have a central role in the interlayer heat transport behavior. A simple phenomenological model, based on local interlayer distance and stacking, captures well the dependence of vertical heat conductance on strain and twist deformations.
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All authors Wenwu Jiang, Huasong Qin, Yilun Liu, Wengen Ouyang, Oded Hod, Michael Urbakh
Materials Science
Accelerated Prediction of Surface Stability and Particle Morphology in Ionic Crystals via Electrostatic Screening
Sourav Baiju and Payam Kaghazchi
This work presents a fast and scalable approach for predicting surface stability and
equilibrium crystal morphology in ionic materials using electrostatic analysis. The method constructs stoichiometric slab terminations and evaluates their electrostatic energies, enabling high-throughput screening of surface configurations at a fraction of the cost of conventional approaches. Polar surfaces are identified through surface dipole moment calculations and stabilized via electrostatics-based reconstruction using replica-exchange Monte Carlo simulations. The surface dipole moment further emerges as an effective descriptor to distinguish the behavior of different classes of materials. By bypassing expensive Density Functional Theory (DFT) calculations, the approach extends naturally to large systems and high-index surfaces that are typically inaccessible to DFT. Electrostatic interactions are shown to capture the dominant trends in relative surface stability across diverse material systems. The method is validated on simple and complex 3D materials as well as 2D layered
oxides, where the predicted dominant facets are consistent with reported density functional theory and experimental observations. Importantly, the framework also reveals cases where high-index surfaces play a non-negligible role in the
equilibrium morphology. These results establish electrostatics as a fast and reliable route for high-throughput prediction of surface stability and particle morphology, opening a pathway for accelerated materials discovery and providing a robust starting point for more detailed calculations in complex energy materials.
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Materials Science
Influence of strain on the anomalous Hall and Nernst effects in Fe thin films
Ao Nakagawa, Ryo Toyama, Keisuke Masuda et al. (+6 more)
The anomalous
Hall effect (AHE) and anomalous Nernst effect (ANE) are the transverse transport phenomena in
magnetic materials, which reflect the Berry
curvature arising from the electronic structure near the
Fermi level.
Lattice strain provides a direct means to tune these effects by modifying the electronic structure; however, disentangling the strain-induced effect through the Berry
curvature modulations in multicomponent materials is challenging due to complexities arising from extrinsic contributions by
impurities and disorder, as well as difficulties in simple direct comparison with first-principles calculations. In this study, we focus on Fe, a prototypical single element ferromagnet with a well-established electronic structure, and tune the sign and magnitude of the strain in epitaxial thin films of by varying the substrates and deposition conditions to investigate the strain effect on the AHE and ANE. Scaling law analysis revealed that the intrinsic anomalous
Hall conductivity (AHC) exhibits a clear tetragonal distortion (c/a) dependence, in good agreement with theoretical calculations based on Berry
curvature modification. In contrast, the anomalous Nernst conductivity (ANC) shows a pronounced deviation from the theoretical values and markedly different c/a dependence. These results demonstrate a crucial difference in the physical origin between the AHC and the ANC in the Fe films; the AHC is predominantly governed by intrinsic mechanisms, whereas the ANC is strongly influenced by the extrinsic contribution.
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All authors Ao Nakagawa, Ryo Toyama, Keisuke Masuda, Weinan Zhou, Hirofumi Suto, Kodchakorn Simalaotao, Yoshio Miura, Yuya Sakuraba, Tetsunori Koda
Materials Science
Coexistence of d-Wave Altermagnetism and Topological States in Janus FeSeX (X = S, Te) Monolayers
Alvaro Gonzalez-Garcia, William Lopez-Perez, Paola Pacheco et al. (+2 more)
The interplay between unconventional magnetism and band
topology in two-dimensional materials has emerged as an important theme in condensed matter physics. Here, we present first-principles calculations that reveal the coexistence of d-wave altermagnetism and topological behavior in Janus FeSeX (X = S, Te) monolayers. The chemical asymmetry of the Janus structure breaks both out-of-plane mirror and inversion
symmetries, leading to anisotropic exchange interactions and momentum-dependent
spin splittings even in the absence of
spin-orbit coupling, the defining signature of altermagnetism.
Phonon dispersion analyses confirm the dynamical stability of both compounds, while strain-dependent calculations demonstrate that the magnitude of the altermagnetic exchange splitting ($\Delta_s$) can be efficiently tuned by biaxial strain. When
spin-orbit coupling is included, a finite topological band gap emerges at the
Fermi level, accompanied by quantized
spin Hall conductivity plateaus and nontrivial topological invariants (
spin Chern number = 1, Z2=1). These findings establish FeSeS and FeSeTe as promising two-dimensional platforms for realizing topological altermagnetism and
spin–orbit–driven charge–
spin conversion, thus opening new avenues for low-dissipation spintronic devices.
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All authors Alvaro Gonzalez-Garcia, William Lopez-Perez, Paola Pacheco, Luz Ramirez-Montes, Rafael Gonzalez-Hernandez
Materials Science
All-organic self-separating three-dimensionally nanoarchitected electrochemical energy storage devices
William R. T. Tait, Sriram Murali, Chao-Hua Hsu et al. (+6 more)
This work realizes a three-dimensionally (3D) nanoarchitected, all organic, "self-separating" lithium-ion electrochemical energy storage (EES) device that is cycled as a solid-state full
cell. The device is enabled by a monolithic carbon anode with a co-continuous pore network, derived from the structure direction of resols by an ultra-large molar mass block copolymer (BCP), poly(styrene-block-2-dimethylaminoethyl methacrylate) (SA). Electropolymerization of a single-phase conductive and redox-active material, poly((2,3-dihydrothieno[3,4-b][1,4]dioxin-2-yl)methyl 9,10-dioxo-9,10-dihydroanthracene-2-carboxylate) (PAQEDOT), into the pore space provides the cathode of the
cell. The device is electronically contacted to the relevant electrode network enabled by the co-continuous nature of each electrode. Electrochemical processing via cycling against external lithium in an electrolyte generates a solid electrolyte interphase (SEI) as a separator and lithiates the
cell electrodes, after which the EES device is cycled in the solid state. While the full
cell does not demonstrate high cyclability, the best full
cell demonstrates a discharge capacity of 267 milliamp hours per gram (mAh/g). This work marks, to the best of knowledge of the authors, the first example of an all-organic materials derived 3D nanoarchitected EES device, as well as the first design of "self-separating"
cell fabrication. Furthermore, generalization of the design to another co-continuous carbon form factor is demonstrated.
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All authors William R. T. Tait, Sriram Murali, Chao-Hua Hsu, Jantakan Nedsaengtip, Christina Lee, R. Paxton Thedford, Vibha Kalra, Joerg G. Werner, Ulrich B. Wiesner