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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Thursday 4 June

Materials Science

Ferroelectric brightening of spin forbidden dark excitons in a WSe2/hybrid perovskite heterostructure

Xinyun Wang, Magdalena Grzeszczyk, Maxim Trushin et al. (+14 more)

Long-lived dark excitons in monolayer WSe2 present promising candidates for carrying spin and valley information, but their optical access and spin manipulation have conventionally required the use of strong external magnetic fields. Here, using a ferroelectric hybrid perovskite heterostructure, we leverage the ferroelectric proximity effect to break the WSe2's in-plane rotational symmetry and brighten the spin-forbidden dark excitons under zero magnetic field conditions. Furthermore, we show that the twist angle between the WSe2 and perovskite crystals controls the ferroelectric coupling strength and valley-contrasting polarization. Our proposed mechanism, supported by a four-band tight-binding model, suggests that the ferroelectric proximity effect induces an asymmetric intersublattice interaction, generating an effective in-plane spin-orbit coupling (SOC) field that rotates spin/valley polarization and brightens dark excitons. Our work establishes ferroelectric proximity coupling as an electrically reconfigurable, magnetic-field-free strategy for spin exciton control in two-dimensional semiconductors.
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All authors Xinyun Wang, Magdalena Grzeszczyk, Maxim Trushin, Ivan Verzhbitskiy, Dmitrii Litvinov, Yi Wei Ho, Yuan Chen, Zhenyue Wu, Mykola Telychko, Chuanqi Zhang, Andres Granados del Aguila, Kuan Eng Johnson Goh, Xinwei Li, Goki Eda, Shaffique Adam, Maciej Koperski, Kian Ping Loh

Materials Science

Resolving room temperature microscale fracture and plasticity of iron oxides along the cascade of iron ore reduction via nanoindentation and microcantilever bending

Shreehard Sahu, James P. Best, Gerhard Dehm et al. (+1 more)

Understanding the fundamental mechanical behaviour of iron oxide phases is essential for controlling attrition and fracture during iron ore reduction process, particularly in hydrogen-based direct reduction systems. This study investigates the room temperature plasticity and fracture behaviour of single-crystal hematite, magnetite, and Wustite using nanoindentation and micro-cantilever fracture testing. Hematite exhibited the highest hardness, H and elastic modulus, E (H=18.5 GPa, E=281 GPa), followed by magnetite (H=8.7 GPa, E=165 GPa) and Wustite (H=7.5 GPa, E=145 GPa), reflecting differences in slip activity along the iron oxide reduction sequence. Furthermore, fracture toughness was measured using notched microcantilevers for all three iron oxide phases, aligned along low index and high index crystallographic planes, respectively. For the low index-oriented case hematite showed increased fracture toughness owing to crack deviation and faceting while magnetite and Wustite exhibited single plane cleavage fracture. Distinct changes in the deformation behavior in terms of plasticity and cracking of the three iron oxides were evident from both methods. Further investigation of a magnetite-gangue interface, particularly relevant to low-concentration ores, revealed significantly reduced fracture toughness compared to the magnetite phase. Overall, these results provide a comprehensive set of mechanical properties of iron oxides with potential application in material models for predicting fracture and attrition during hydrogen-based direct reduction.
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All authors Shreehard Sahu, James P. Best, Gerhard Dehm, Anwesha Kanjilal

Materials Science

The KNN rollercoaster: from bulk ceramics to phase engineered wafer-scale thin films

Giulia Pavese, Federico Orlando, Fabio Melzi et al. (+12 more)

Since the initial disclosure of the extraordinary piezoelectric coefficients of Potassium sodium niobate (KNN) in near-equimolar bulk ceramics, its development trajectory has resembled a rollercoaster, with its integration into microelectronics severely lagging due to thermodynamic stability issues and poor planar process compatibility. In this work, we revisit the bulk-derived phase diagram for the specific case of thin films integrated on silicon. By systematically investigating Mn-doped K1-xNaxNbO3 films grown on 8-inch wafers, we demonstrate that the optimal stoichiometry for thin films fundamentally diverges from the bulk equimolar standard. A Na-rich composition (> 70 at.%) is required to overcome substrate-induced constraints, effectively suppressing pyrochlore formation and chemical phase segregation while promoting dense columnar growth with a complete (001) out-of-plane polar orientation. Consequently, Na-rich films deliver outstanding functional properties, reaching remanent polarizations up to 14 uC cm-2, with piezoelectric coefficients of d33f= 79 pm/V and e31f = 10 C/m2. Supported by Density Functional Theory simulations, we correlate this enhancement with improved stability and a strain-driven structural reorientation toward a lower-symmetry monoclinic phase with tilted polarization. By redefining the phase engineering rules for wafer-scale thin films, our results establish a clear route toward KNN integration in microsystems.
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All authors Giulia Pavese, Federico Orlando, Fabio Melzi, Walter Piazzi, Andrea Pescarolo, Federico Maspero, Marco Asa, Riccardo Gianola, Andrea Picco, Andrea Serafini, Kui Yao, Silvia Picozzi, Laura Castoldi, Miguel-Ángel Badillo-Ávila, Riccardo Bertacco

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

Coupled simulation of plasma-surface interactions during early stages of vacuum arcing

Roni Koitermaa, Andreas Kyritsakis, Tauno Tiirats et al. (+2 more)

We describe fully coupled simulations that bridge atomistic cathode dynamics and plasma formation during the earliest stages of vacuum arcing. The model combines molecular dynamics, finite element electrothermal calculations, electron emission and particle-in-cell plasma simulations via dynamic transfer of particles between the surface and plasma domains. Simulations of Cu nanoprotrusions reveal two routes to thermal runaway: direct Joule heating-driven instability and a novel nanoparticle-assisted mechanism, where detached nanoparticles generate neutral vapor that becomes ionized.
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All authors Roni Koitermaa, Andreas Kyritsakis, Tauno Tiirats, Flyura Djurabekova, Veronika Zadin

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

Odd-parity magnons in the Haldane-Hubbard model from topological exciton condensation

Rintaro Eto and Johannes Knolle

Odd-wave magnets are the counterparts to even-wave altermagnets realizing odd-parity spin splitting. Normally discussed for noncollinear systems, they have recently been shown to appear in collinear magnetic states in the presence of loop currents. Here we study collective excitations of the paramagnetic and magnetic phase of the seminal Haldane-Hubbard model. We identify the existence topological excitons in the paramagnetic phase, and their condensation as the driving mechanism into the collinear Néel state. The latter realizes an odd-wave magnet with odd-parity magnons displaying a characteristic $f$-wave splitting. We further uncover that an electron bandgap closing ensures magnon bandgap closing causing a change in odd-parity magnon topology, as well as a drastically enlarged spin splitting. Our results establish the presence of topological excitons and odd-parity magnons in the Haldane-Hubbard, with potential realizations in Floquet-driven materials and cold atomic gases.
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Materials Science

Strong Optical-Optical Avoided Crossings Suppress Thermal Conductivity in Ga-Substituted TlInTe$_2$

Sayan Paul and Swapan K Pati

In crystalline solids, avoided crossing between acoustic and optical phonons is widely recognized as an effective mechanism for suppressing lattice thermal conductivity ($\kappa_l$). However, the role of avoided crossings among optical phonons remains largely unexplored due to their weak contribution to heat transport. Here, using first-principles calculations combined with the linearized Wigner transport equation (LWTE), we demonstrate that optical-optical avoided crossings can effectively reduce ($\kappa_l$) in TlIn$_{0.5}$Ga$_{0.5}$Te$_2$. Pristine TlInTe$_2$ exhibits strong optical phonon-dominated heat transport, where optical phonons contribute nearly 63% of $\kappa_l$. The phonon dispersion of TlInTe$_2$ shows several crossing points in the optical region, which evolve into avoided crossings after 50% Ga substitution. Irreducible representation analysis reveals that the crossing phonon branches in TlInTe$_2$ belong to different symmetry representations, whereas the corresponding branches in TlIn$_{0.5}$Ga$_{0.5}$Te$_2$ possess the same symmetry representation, which enables phonon modes to couple and results in gap opening at the crossing points. These avoided crossings significantly suppress the optical phonon group velocity, thereby reducing the optical phonon contribution from 63% to 44% and lowering $\kappa_l$ from 0.568 to 0.482 Wm$^{-1}$K$^{-1}$ at 300 K. Mode-averaged transport analysis further confirms that the suppression of $\kappa_l$ is primarily governed by reduced phonon group velocity ($v_g$), while enhanced anharmonic scattering provides an additional secondary contribution. Our results establish symmetry-modified optical-optical avoided crossing as an effective route to suppress optical phonon transport and reduce $\kappa_l$ in systems where optical phonons significantly contribute to heat transport.
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Materials Science · Cross-listed from cond-mat.supr-con

BCS-BEC crossover driven by small Fermi pockets of a high-Tc cuprate superconductor

Junhyeok Jeong, Yamato Enomoto, Yoshimitsu Kohama et al. (+16 more)

Fermi arcs observed in underdoped cuprates have sparked debate over whether they represent segments of a large Fermi surface or small Fermi pockets. This ambiguity has long hindered their classification as either the conventional Bardeen-Cooper-Schrieffer (BCS) regime or the strongly coupled Bose-Einstein condensation (BEC) crossover limit. Here, using angle-resolved photoemission spectroscopy and quantum oscillations, we demonstrate the coexistence of a small Fermi pocket and a large superconducting gap in the clean inner CuO2 layers of the four-layer cuprate Ba2Ca3Cu4O8(F,O)2. This coexistence constitutes a hallmark of the BCS-BEC crossover and has remained elusive for decades. Despite the presence of antiferromagnetic (AF) order, the superconducting gap in the small pocket is remarkably large, yielding a gap-to-Fermi-energy ratio (Delta_pocket/e_F ~ 0.6) and a critical-to-Fermi-temperature ratio (Tc/TF ~ 1.3) that reach the theoretical upper bound for two-dimensional superconductivity. Unexpectedly, this BCS-BEC crossover emerges not as the carrier density decreases but as it increases, abruptly within a narrow doping range of less than 1%. These results provide a long-sought microscopic foundation for the d-wave pairing mechanism in doped AF-Mott insulators.
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All authors Junhyeok Jeong, Yamato Enomoto, Yoshimitsu Kohama, Tomotaka Nakayama, Kotaro Ando, Kifu Kurokawa, Soonsang Huh, Zhuo Yang, Toshihiro Nomura, Matthew D. Watson, Timur K. Kim, Cephise Cacho, Chun Lin, Makoto Hashimoto, Donghui Lu, Shiro Sakai, Takami Tohyama, Kazuyasu Tokiwa, Takeshi Kondo

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

HVPE Growth of Si-Doped $\beta$-Ga$_2$O$_3$ on Sapphire: Influence of Substrate Offcut on Structural and Electrical Properties

Sourav Sarker, Saleh Ahmed Khan, Ahmed Ibreljic et al. (+1 more)

Si-doped $\beta$-Ga$_2$O$_3$ films were heteroepitaxially grown on sapphire substrates using HVPE. The influence of sapphire offcut on growth kinetics, surface morphology, crystalline quality, and electrical transport properties was systematically investigated. Growth kinetics studies revealed a strong dependence of deposition rate on HCl flow, growth pressure, and source-to-substrate distance, with growth rates reaching up to 30 $\mu$m/hr. Increasing sapphire offcut angle from 0$^\circ$ to 8$^\circ$ promoted a transition from multidirectional growth to highly aligned terrace-dominated surfaces, reducing the surface roughness from 14.69 to 2.74 nm. The improved surface morphology was accompanied by enhanced crystalline quality, with phase-pure (-201)-oriented $\beta$-Ga$_2$O$_3$ growth and a reduction in the rocking-curve full width at half maximum from 994 to 414 arcsec as the sapphire offcut increased. Electrical characterization of films grown on 6$^\circ$ offcut substrates yielded carrier concentrations ranging from $1.0\times10^{17}$ to $3.4\times10^{18}$ cm$^{-3}$. A maximum room-temperature electron mobility of 100cm$^2$/V$\cdot$s was achieved at a carrier concentration of $1.0\times10^{17}$cm$^{-3}$, representing the highest reported room-temperature mobility for HVPE-grown $\beta$-Ga$_2$O$_3$ on a foreign substrate. Analysis of the temperature-dependent transport characteristics yielded donor activation energies of 35 and 90 meV together with a low acceptor concentration of $3\times10^{15}$ cm$^{-3}$, consistent with the improved crystalline quality achieved on the offcut sapphire substrates. These results demonstrate that HVPE is capable of producing high-quality $\beta$-Ga$_2$O$_3$ heteroepitaxial layers with good crystalline quality and carrier transport characteristics, providing a promising pathway for scalable $\beta$-Ga$_2$O$_3$ epitaxy on low-cost foreign substrates.
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All authors Sourav Sarker, Saleh Ahmed Khan, Ahmed Ibreljic, Anhar Bhuiyan

Wednesday 3 June

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

Realistic quantum device data synthesized by consumer AI and how to identify it

S. M. Frolov and O. V. Kravchenko

With the advance of generative artificial intelligence (AI) synthetic texts and images have become commonplace. These capabilities offer clear benefits, but have also raised a number of ethical concerns that often have to do with misrepresenting AI outputs as genuine material. A lesser known capability of generative AI is to perform the basic analysis, processing and even synthesis of numerical data. This raises the question of whether AI can be used to imitate experimental data that an expert would consider scientifically meaningful and on par with data in the figures of peer-reviewed manuscripts? In this paper, we focus on synthesizing data inspired by well-known experiments done frequently on quantum electronic devices. This field is related to information technologies such as spintronics and quantum computing, and is considered data-rich and data-driven. We demonstrate that it is possible to generate dramatic signals associated with iconic effects such as quantum bit control, Majorana fermions, Josephson effects, quantum dots and wires using widely available ChatGPT. We find that because some of the clearest data from quantum devices can be expressed in terms of relatively basic mathematical models, AI does not need to learn on the specialized body of data. Instead, knowledge of the physics equations and of the basic features of experimental signals can go a long way towards building a realistic dataset. We also demonstrate that real data can be augmented by AI, and that AI can mimic the noise of common scientific instruments. To help assure that published data come from experiments and are not synthesized by AI, we recommend sharing large volumes of the primary data. While it is straightforward for AI to mimic a few sets of data, consistently generating long measured sequences poses sufficient barriers to the proliferation of undisclosed synthetic data.
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Materials Science

Interplay of non-local transport and local scattering during electron thermalization and spatial equilibration in laser-excited metals

Markus Uehlein, Tobias Held, Christopher Seibel et al. (+2 more)

Ultrafast laser excitation of metals induces electronic nonequilibrium both in space and locally in the energy distribution. The subsequent dynamics are governed by the interplay between non-local transport and local scattering of hot electrons, yet combined microscopic descriptions of these processes remain sparse. Here, we disentangle the influence of these processes on thermalization using a reformulation of the Boltzmann transport equation in energy space that consistently describes both spatial equilibration and scattering through full collision integrals. Our results reveal that transport accelerates the apparent thermalization observed at the irradiated surface by removing athermal carriers, while the same spatial redistribution delays complete equilibration of the full electron system. We analyze the experimentally accessible energy-dependent dynamics at the front and back surface and find that the dominant process varies, depending on both position and on the energetic window. Overall, our work improves the understanding of the interplay of electronic nonequilibrium processes occurring in optically thick laser-driven systems with relevant implications for future electronic applications.
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All authors Markus Uehlein, Tobias Held, Christopher Seibel, Sebastian T. Weber, Baerbel Rethfeld

Materials Science

Hydrogen-induced lattice cohesion weakening favors atomic displacement

Liang Gao, Yiran Mao, Markus Wilde et al. (+9 more)

Atomic displacement – the fundamental process underlying diverse deformation and damage phenomena in metals, from irradiation defect production to stress-driven dislocation motion – is governed by interatomic cohesion strength. Here, lattice-dissolved hydrogen (LDH) occurring in metals under direct hydrogen exposure is identified to effectively weaken lattice cohesion, and thereby facilitating atomic displacement and dislocation movement upon plastic deformation in sub-threshold stress regime. This atomic-scale insight provides a physically transparent mechanism for hydrogen-enhanced localized plasticity implicated in hydrogen embrittlement. We quantitatively verify the hydrogen-induced lattice cohesion weakening effect on metal surfaces exposed to low-energy hydrogen plasma, where massive defects are generated despite the absence of sufficient ion momentum for direct displacement damage. By unprecedentedly quantifying the cohesion-weakening effect of LDH independently from defect-trapped H, we establish a new paradigm to understand hydrogen embrittlement.
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All authors Liang Gao, Yiran Mao, Markus Wilde, Xiaoou Yi, Cong Li, Shiwei Wang, Thomas Schwarz-Selinger, Jan Coenen, Richard Kembleton, Sebastijan Brezinsek, Christian Linsmeier, Guanghong Lu

2606.05325 · 3 Jun · We reveal here the exact role of diffusive lattice-dissolved hydrogen (LDH) favoring kink pair nucleation and accelerating dislocation movement, unlocking the underlying nature of the HELP (Hydrogen-Enhanced Localized Plasticity) mechanism. Main text 17 pages, 4 figures; Supplementary Materials 9 pages, 2 figures

Abstract PDF $LATT ×4$PLSM ×1

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

Magnetic-field driven hybridization of heavy- and light-hole Rydberg excitons in GaAs quantum wells

David de la Fuente Pico, Johannes Bürger, Antonio Gianfrate et al. (+5 more)

We present a combined theoretical and experimental study of ground and excited Rydberg exciton states in wide GaAs quantum wells exposed to a magnetic field in the Faraday geometry. We employ a multiband exciton model based on the Luttinger Hamiltonian, which captures valence-band mixing between heavy- and light-hole states induced by both the quantum well confinement and the magnetic field, and we develop an efficient numerical approach to solve for both ground- and excited-state excitons. The method treats Coulomb interactions, magnetic confinement, and band mixing on an equal footing, enabling a systematic characterization of exciton energies, oscillator strengths, and orbital composition. We show that band hybridization increases with magnetic field and is significantly more pronounced for higher excited states, where it sets in at lower fields and strongly modifies their properties. The theoretical predictions are validated by polarization-resolved magneto-reflectance measurements up to 9 T on GaAs/Al$_{0.4}$Ga$_{0.6}$As quantum wells of 20 nm width. We find excellent agreement for both the diamagnetic shift and Zeeman splitting of the ground state and the first four Rydberg excitons. Our results demonstrate that valence-band mixing plays a crucial role in determining the magnetic-field dependence of excited exciton states and must be properly included for a quantitative description of magneto-excitons in wide GaAs quantum wells.
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All authors David de la Fuente Pico, Johannes Bürger, Antonio Gianfrate, Jesper Levinsen, Meera M. Parish, Daniele Sanvitto, Dario Ballarini, Francesca Maria Marchetti

Materials Science

MicroCup: A Cryogenic Specimen Preparation Strategy for Atom Probe Tomography of Organic Molecular Liquids

Kuan Meng, Florian Groll, Sebastian Eich et al. (+1 more)

Atom probe tomography (APT) of organic molecular liquids is limited by poorly reproducible specimen geometry, reduced milling rates, and beam sensitivity during cryo-FIB preparation. Here we introduce a MicroCup strategy that confines liquids in a FIB-prepared nanoscale cavity prior to phase separation, reduces deposited volume to increase preparation throughput, enables reproducible specimen geometry, and minimizes beam exposure in the region of interest. Using the liquid crystals 4'-octyl-4-cyanobiphenyl (8CB) and 4'-octyloxy-4-cyanobiphenyl (8OCB) as model systems, we establish stable and reproducible field evaporation conditions, enabling the detected intact ion molecular preservation above 70% in smectic-like phases with interpretable fragmentation behavior. Comparative analysis further shows that the oxygen atom in 8OCB promotes preferential cleavage pathways associated with bond polarization under high electric fields. By inducing partial crystallization within the MicroCup cavity, distinct regions could be resolved: 8CB shows broadly similar evaporation behavior across crystalline and amorphous regions, whereas 8OCB exhibits clearer regional contrast, with smectic-like regions dominated by intact molecular or large fragments and crystalline domains producing small alkyl fragments and ether-type species. These results provide spatially resolved evidence of a solid-liquid interface in a freeze-prepared organic liquid by APT and establish a reproducible workflow for probing local phase behavior in soft materials.
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All authors Kuan Meng, Florian Groll, Sebastian Eich, Guido Schmitz

Materials Science

Density-functional theory calculation of hydrogen solubility in cubic silicon carbide at finite temperatures

Jonathan S. Evarts, Anne Chaka and Towfiq Ahmed

An ab initio framework using density-functional theory has been developed to predict hydrogen solubility in both pristine and defective e̱ta}-SiC. This study is motivated by the critical need for accurate hydrogen permeation models in fusion reactor designs, where predicting hydrogen permeation through tritium permeation barrier (TPB) materials is essential. Although silicon carbide is one of the leading candidates for TPBs, experimental permeation values vary widely due to differences between ideal single crystals and real, defect-containing materials. First principles calculations are employed to quantify the effects of interstitials, vacancies, and nonstoichiometric (amorphous) structures on hydrogen behavior in e̱ta}-SiC. Our results show that hydrogen solubility is significantly enhanced in carbon-rich nonstoichiometric amorphous structures and silicon vacancies compared to hydrogen occupying interstitial sites in pure e̱ta}-SiC.
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Materials Science · Cross-listed from cond-mat.mes-hall

Exchange-mediated exciton splitting and linear dichroism in monolayer transition metal dichalcogenide induced by ferroelectric substrates

Sudipta Kundu and Felipe H. da Jornada

Valley-polarized excitons in two-dimensional transition metal dichalcogenides (TMDs) offer a promising platform for quantum applications, yet the addressability and decoherence of these states remain fundamental challenges. Here, by developing a first-principles electrostatic embedding approach and performing large-scale GW plus Bethe-Salpeter equation calculations, we reveal novel excitons that emerge in TMD monolayers when supported by a ferroelectric twisted bilayer hBN substrate. We predict two competing low-energy excitons whose ordering depends on the dielectric environment: optically dark, charge-transfer excitons, and quasi-one-dimensional Wannier excitons with linear optical dichroism. The spatial localization of Wannier excitons, together with intervalley exchange interactions in monolayer TMDs, splits valley-degenerate excitons by about 3~meV without external magnetic fields. Our ab initio calculations clarify the role of the interfacial twist angle and the spatial localization of fringe fields, establishing design rules for engineering long-lived two-level systems in TMD monolayers supported by ferroelectric substrates.
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Materials Science

Mechanoluminescence in crystalline inorganic materials: local disorder and the elastic distortion hypothesis

T. Rouxel, X. Rocquefelte and S. Tanabe

In this exploratory work, we aim to understand the mechanoluminescence (ML) phenomenon manifested by various inorganic compounds by focusing on the influence of mechanical loading on local distortion and loss of symmetry at active sites. To this end, we have analyzed the elastic deformation of several relevant crystalline phases and shown, through a kinematic analysis based on elastic constants, that the loading-induced distortion is smaller than, but remains comparable in magnitude to, the intrinsic structural distortion as quantified by the Baur descriptor. Although the structural distortion has previously been proposed as a structural fingerprint of the ML potential of a compound, it is by nature a static parameter, and must be supplemented by a dynamic distortion contribution that develops under mechanical load. By approximating the crystal deformation by that of simple polygonal motifs, we have been able to propose a rationale for otherwise puzzling observations: in particular, the marked differences in sensitivity to hydrostatic pressure and to shear, the appearance of an intense ML peak upon unloading in certain compounds, and the contrast in behavior depending on whether the preliminary UV irradiation is performed under load or at rest.
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Materials Science · Cross-listed from cond-mat.mes-hall

Bulk and surface excitons in the van der Waals magnet CrSBr: Magneto-optical studies to 55 tesla

Junho Choi, Yihyun Moon, Doohyeon Lee et al. (+4 more)

In thin layers of the 2D magnetic semiconductor CrSBr, very recent studies identified two distinct band-edge optical resonances, believed to arise from distinguishable bulk and surface excitons. This behavior reportedly originates from the highly anisotropic nature of CrSBr – particularly in its antiferromagnetic state – where excitons are effectively confined within individual monolayers, such that excitons in the two surface layers "see" a different local dielectric environment and have a lower resonance energy. To explore this scenario, here we investigate optical absorption properties of few-layer CrSBr in magnetic fields. In addition to the fundamental exciton resonance at ~1.36eV, we observe an absorption resonance ~20 meV lower in energy. Compared to the fundamental transition, this resonance redshifts only half as much in small magnetic fields that induce ferromagnetic order, while in high fields to 55T it exhibits a smaller diamagnetic shift. Both behaviors point to distinguishable populations of bulk and surface excitons in CrSBr.
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All authors Junho Choi, Yihyun Moon, Doohyeon Lee, Iva Plutnarova, Zdenek Sofer, Vinod M. Menon, Scott A. Crooker

Materials Science

Autonomous heterogeneous catalyst discovery with a self-evolving multi-agent digital twin

Zhilong Song, Zongmin Zhang and Lixue Cheng

Theoretical heterogeneous catalysis promises rapid catalyst discovery, yet computational and machine-learning predictions often deviate from experiment and stay confined to narrow material families, for want of a faithful, condition-aware catalytic simulator. We present CatDT (Catalysis Digital Twin), a self-evolving multi-agent system that builds an autonomous digital twin of a working catalyst, unifying gas-solid and liquid-solid modeling. From only a bulk crystal and a natural-language reaction description, eight specialized agents and 27 scientific tools predict stable facets, reconstruct working surfaces, enumerate and rank reaction pathways, locate transition states, and compute kinetics in 5-30 min on a single GPU. Two innovations address the hardest steps: UniMech finds dominant pathways for novel materials at over $10^3\times$ lower cost than exhaustive enumeration by fusing agent-guided proposals with energy-cached graph search, and a memory-augmented reinforcement loop raises barrier-calculation success from 41% to 84% across 600 catalytic surfaces. Across seven gas-solid benchmarks – stepped metals, single-atom catalysts, ordered intermetallics, vacancy-rich 2D sulfides and carbides, and a strong-metal–support-interaction (SMSI) interface – every CatDT prediction lies within 0.5-2 times experiment over four orders of magnitude. For propane dehydrogenation, CatDT independently discovers non-precious candidates rivaling the Pt-based industrial benchmark, with a proposed Ni@ZrO$_2$ SMSI overlayer reaching a simulated TOF of $1.63~\text{s}^{-1}$ at $\sim$100% selectivity. More broadly, the decisive factor for a faithful catalyst digital twin – or any multi-stage scientific simulator – is not raw LLM capability but the engineered harness around it: deterministic tools, persistent memory, and verified self-improvement that compound across models, tools, and runs.
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Materials Science

Berry-Curvature Activation by Orbital Flux in a Kagome Altermagnet

Meysam Bagheri Tagani and Carmine Autieri

We investigate topological electronic responses in a kagome altermagnetic metal hosting a compensated coplanar $120^\circ$ magnetic texture. Using a minimal tight-binding model containing nearest-neighbor hopping, noncollinear exchange coupling, intrinsic spin–orbit coupling, and a time-reversal-odd loop-current order, we disentangle the magnetic, orbital, and relativistic mechanisms governing the electronic response. The exchange field produces pronounced momentum-dependent spin splitting and spin-polarized Fermi surfaces without generating a net magnetization. Nevertheless, in the absence of loop-current order, a hidden antiunitary symmetry $\mathcal{T}C_{2z}$ enforces vanishing Berry curvature and intrinsic anomalous Hall conductivity, even for finite spin–orbit coupling. A directed imaginary bond order breaks this protection and activates finite Berry curvature and a sizable, strongly filling-dependent Hall response already in the nonrelativistic limit. Spin–orbit coupling subsequently reconstructs the avoided crossings and redistributes the Berry curvature, enhancing or suppressing the Hall response depending on filling. For sufficiently strong loop-current order and spin–orbit coupling, a global gap opens at $n_e=3$, and the Hall conductivity approaches $2e^2/h$, consistent with an occupied-band Chern number of magnitude two. Parameter-space and filling-dependent calculations further demonstrate that the Hall-active regime extends over broad ranges of exchange coupling, spin–orbit coupling, and chemical potential and remains robust against symmetry-preserving longer-range hopping. These results identify orbital-current order as an independent route for converting a Hall-silent kagome altermagnet into an anomalous Hall metal or a gapped topological phase without net magnetization, noncoplanar spin order, or scalar spin chirality.
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Materials Science

SLUSCHI-UP: A Web Infrastructure for SLUSCHI Melting-Temperature Calculations Using Universal Machine-Learning Interatomic Potentials

Qi-Jun Hong

Melting temperature is a critical property for high-temperature materials design, but first-principles melting calculations based on finite-temperature molecular dynamics can require substantial computational resources. The SLUSCHI method reduces this cost by using small-cell solid–liquid coexistence simulations and statistical analysis of many short molecular-dynamics trajectories. Here I present SLUSCHI-UP, a deployed web service for atomistic melting-temperature estimation that couples the SLUSCHI workflow to selectable pretrained universal machine-learning interatomic potentials (uMLIPs) and asynchronous GPU execution. Users submit a crystal structure through a Materials Project identifier or POSCAR input, select a uMLIP backend, and launch a queued melting calculation without local installation of simulation software. The current production interface supports mace-mpa-0-medium, Allegro-OAM-L, and DPA-3.2-5M-OMat24, while beta deployments expose additional models. On the compact MeltBench-10 validation set, the three production backends produce raw coexistence mean absolute errors in the range of approximately 178–327 K. Across the broader set of materials tested so far in MeltBench, the current deployed-job snapshot contains 119 raw uMLIP entries, and PBE-corrected Allegro-OAM-L predictions reach a mean absolute error of approximately 166 K. These values should be interpreted as screening-level infrastructure validation rather than a definitive ranking of uMLIPs. The results demonstrate that SLUSCHI-UP provides a practical, provenance-aware deployment layer between fast scalar melting-temperature predictors and much more expensive first-principles coexistence calculations, while retaining the usual limitations of uMLIP transferability, finite-size sampling, and high-temperature trajectory stability.
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Materials Science · Cross-listed from cond-mat.mes-hall

Very strong light-matter coupling in patterned GaAs heterostructures

David de la Fuente Pico, Johannes Bürger, Antonio Gianfrate et al. (+5 more)

The very strong light-matter coupling regime enables the non-perturbative modification of matter properties via light. Using a patterned GaAs/AlGaAs waveguide with twelve wide quantum wells, we demonstrate hybridization of heavy- and light-hole excitons within a single polariton state and show that, at finite magnetic field, the presence of the light-hole exciton suppresses coupling to the heavy-hole Rydberg excitons and unbound scattering states. We develop a fully microscopic theory that accounts for the combined effects of the magnetic field and light-matter coupling on the excitons, providing an accurate description of the experimental results beyond a perturbative coupled-oscillator framework. This identifies quantum well width as a key control parameter for engineering the light-induced hybridization of matter wave functions in polaritons, which, in turn, can play a crucial role in the optical non-linearities.
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All authors David de la Fuente Pico, Johannes Bürger, Antonio Gianfrate, Jesper Levinsen, Meera M. Parish, Daniele Sanvitto, Francesca Maria Marchetti, Dario Ballarini

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

Tunable Resonator Integrated Magnetometry

Colin Stack, Brian Sears, Aruna Ramanayaka et al. (+3 more)

The quantum-technology revolution is reshaping computing, sensing, and communication. In magnetometry, recent advances leverage precise control of spin qubits and color centers in solid-state crystals for mesoscopic-scale sensing. Yet at very low temperatures, superconducting sensing technology remains unrivaled because of its non-invasiveness and higher sensitivity. Here we describe a class of superconducting sensors that offers low loss and quantum non-demolition measurement characteristics. We designed and fabricated a superconducting flux-tunable resonator (tRes) in a superconducting chip foundry and matured it to a level that combines the speed of an inductor-capacitor circuit with the flux sensitivity of a superconducting quantum interference device (SQUID) to perform magnetometry at milli-kelvin temperature to investigate targets. We introduce its fundamental functionality readily at MHz magnetic sampling rate, showcase two measurement modalities, and investigate three circuits with gradually increasing complexity to extract target-specific information. The combination of high sensitivity and fast readout characteristics make tRes an attractive and versatile magnetometer.
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All authors Colin Stack, Brian Sears, Aruna Ramanayaka, David Ferguson, Ilya Sochnikov, Tony X. Zhou

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

Influence of anisotropy on the expansion performance of auxetic skin meshing geometries: a finite element study

Masoumeh Razaghi Pey Ghaleh, Denis O'Mahoney and Kevin Moerman

This study investigates the combined effects of anisotropy and auxetic mesh geometry on the performance of skin graft expansion. Finite element models of auxetic slit-based geometries were developed and subjected to 25 percent tensile strain. Skin was modelled using an anisotropic constitutive formulation. Langer's line orientations were varied relative to the load direction. Results showed anisotropy strongly influenced expansion behaviour. The effect was observed to be complex and highly dependent on mesh type. Anisotropy was observed to enhance or inhibit the auxetic expansion behaviour. In all mesh types studied, the expansion performance is lowest when Langer's lines align with the transverse direction. Greatest expansion was typically observed when Langer's lines were close to the loading direction. Isotropic models overpredicted stress relative to the anisotropic models. These findings support the use of auxetic structures for skin mesh expansion applications and show that anisotropy is an important factor in both deformation and stress prediction.
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Materials Science

Variational approach to determine the properties of dislocations at finite deformation

István Groma

A generalised version of the continuum theory of curved dislocations describing the spatial and temporal evolution of the fields: statistically stored dislocation density, geometrically necessary dislocation density, and curvature has recently been proposed. The dynamics of the system are derived from a scalar functional of the relevant fields that cannot increase during the evolution of the system. However, the framework was established only for small deformations. The aim of the present paper is to discuss the fundamentals of the elasticity theory of finite deformation in cases where individual dislocations are present in the system. The equilibrium equations are derived within a variational formalism. It is shown that introducing dislocations into the finite deformation framework is a nontrivial task. Moreover, if the deformation is large, the force acting on a dislocation segment is not the well-known Peach-Koehler force. In a forthcoming paper, the results obtained will be applied to the generalisation of the dislocation continuum theory of curved dislocations.
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Materials Science

Barrier-channel intermixing and 2-dimensional electron gas degradation in Al-rich Al(Ga)N/AlGaN high electron mobility transistor heterostructures

Pietro Pampili, Vitaly Z. Zubialevich, Badal Mondal et al. (+4 more)

In this work, we report on recent results in understanding and addressing the issue of interface smearing in high-aluminium content AlGaN/AlGaN heterostructures. On the one hand, the growth of high-crystal quality AlGaN by metal-organic vapour phase epitaxy (MOVPE) requires the use of high temperatures, but on the other hand this may lead to alloy intermixing between barrier and channel layers, which smoothens out the polarization contrast and severely degrades or even completely destroys the 2-dimensional electron gas (2DEG). We show that X-Ray Diffraction (XRD) analysis can be used as a non-destructive way to assess the sharpness of the interface, and that improved growth schemes can be successfully used to achieve high-quality 2DEG, as confirmed by contactless resistivity measurements. In particular, sheet resistivities around 2,500 $\Omega/\Box$ were demonstrated for AlN/Al$_{0.75}$Ga$_{0.25}$N, consistent with the best-reported values in the literature.
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All authors Pietro Pampili, Vitaly Z. Zubialevich, Badal Mondal, Jayjit Mukherjee, Stefan Schulz, David A. J. Moran, Peter J. Parbrook

Materials Science

Machine learning via artificial neural networks coupled with density functional theory and experiments for thermodynamic optimization of high-entropy alloys for hydrogen storage at room temperature

Shivam Dangwal, Pranav Kumar, Yuji Ikeda et al. (+2 more)

High-entropy alloys (HEAs) have received considerable attention for hydrogen storage because of their compositional flexibility; however, designing HEAs with optimal thermodynamics is critical. This study employs machine learning via artificial neural networks (ANN) and density functional theory (DFT) to design a novel AB-type TixNb2-xVCrMnFe (x = 0.5-2.0) high-entropy system for hydrogen storage at ambient temperature (A: Ti, V and Nb, and B: Cr, Mn and Fe). Both ANN and DFT predict that the hydride formation enthalpy decreases to negative values with increasing the titanium content. Two alloys with x > 1.5 are predicted to achieve enthalpies within the -25 to -39 kJ/mol range, making them appropriate for room-temperature hydrogen storage. Experiments demonstrate good agreement with the enthalpy predictions, with the Ti-rich alloys showing reversible hydrogen storage with fast kinetics at room temperature. These results provide a framework for reliable use of data analysis and ab initio calculations to explore high-entropy hydrides as hydrogen storage materials.
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All authors Shivam Dangwal, Pranav Kumar, Yuji Ikeda, Blazej Grabowski, Kaveh Edalati

Materials Science

Strain-induced suppression of thermochromism in divalent cobalt molybdate thin films

Kiri Van Koughnet, Joey Williamson, Kane Hill et al. (+10 more)

Thermochromic oxides provide a platform for coupling lattice, electronic, and magnetic degrees of freedom, with divalent cobalt molybdate $CoMoO_4$ as a prototypical example. Despite extensive studies on powders, its thin-film behaviour - critical for device applications - remains largely unexplored. Here, we present a combined experimental and theoretical investigation of $CoMoO_4$ thin films, including the first THz-VIS-UV spectra of $\beta - CoMoO_4$ in thin-film form. In contrast to bulk powders, which undergo a first order $\beta \rightarrow \alpha$ structural transition near 230K, the thin films retain the high-temperature $\beta-$phase across the entire temperature range. We show that microstrain fundamentally reshapes the phase landscape, suppressing thermochromism and stabilizing the $\beta-$phase. The optical spectra reveal pronounced phonon and electronic anomalies, including a softening of a low-energy, cation-dominated phonon (42cm$^{-1}$) upon cooling, in contrast to conventional mode-hardening. This behaviour indicates incipient atomic displacements analogous to those driving the bulk $\beta \rightarrow \alpha$ transition, despite the absence of a structural phase change, and saturates between 200 and 150K. Temperature-dependent X-ray diffraction confirms persistent \beta-phase symmetry with increasing microstrain, consistent with strain-induced frustration of the first-order transition. At higher energies (0.12-3.7eV), the optical response exhibits a blue-shift of Co$^{2+}$crystal-field transitions and charge-transfer excitations, indicating a strain-enhanced ligand field. Supported by structural refinements and theoretical calculations, we identify crystal field strengthening as the key mechanism stabilizing the $\beta$-phase. These results establish strain as a thermodynamic lever to control phase stability and functional properties in thermochromic oxides.
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All authors Kiri Van Koughnet, Joey Williamson, Kane Hill, Robert G. Buckley, Yurii G. Pashkevich, Sergej M. Orel, Eric Lebraud, Manuel Gaudon, Peter P. Murmu, Sarah Spenser, Dominique Appadoo, Shen V. Chong, Fryderyk Lyzwa

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

Orientation-resolved tunnel spectroscopy of a triplet superconductor

Marcel Strohmeier, Andriy Smolyanyuk, Karsten Held et al. (+5 more)

Although Cooper pairs in superconductors generally condense into a spin-singlet state, spin-triplet superconductivity has attracted sustained interest since it enables dissipationless spin transport and is an important requirement for manifold topological quantum technologies. Noncentrosymmetric superconductors provide a promising route to triplet pairing because their intrinsic antisymmetric spin-orbit coupling (ASOC) can mix spin-singlet and spin-triplet states. To date, the strongest evidence for such mixed-parity superconductivity has been reported in heavy-fermion systems, where strong electronic correlations obscure the role of ASOC. Whether ASOC alone can support a substantial spin-triplet component remains unresolved. Here we show that the weakly correlated noncentrosymmetric superconductor Nb$_{18}$Re$_{82}$ (Nb-Re) hosts a mixed-parity superconducting state with a substantial spin-triplet contribution. Orientation-resolved low-temperature scanning tunneling spectroscopy reveals a strongly anisotropic quasiparticle density of states. A symmetry-constrained analysis shows that the spectroscopic dataset is explained by an order parameter combining a nodal spin-singlet component with a spin-triplet contribution reaching up to half of the singlet amplitude. These findings provide a momentum-resolved determination of a mixed-parity superconducting order parameter and demonstrate that ASOC alone can foster a substantial spin-triplet component. More broadly, they establish orientation-resolved tunneling spectroscopy as a route to identifying mixed-parity superconducting states and suggest that triplet superconductivity may be more widespread among noncentrosymmetric materials than previously recognized.
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All authors Marcel Strohmeier, Andriy Smolyanyuk, Karsten Held, Michael Smidman, Geetha Balakrishnan, Wolfgang Belzig, Elke Scheer, Angelo Di Bernardo

Materials Science

Local multiferroic ordering at room temperature in collinear magnetoelectric antiferromagnets induced by flexo-Zeeman coupling

Paulina J. Prusik, Igor Veremchuk, Florin Radu et al. (+11 more)

Spin-driven multiferroicity attracts significant interest due to its tunability and inherently strong magnetoelectric coupling. While this mechanism induces sizeable electric polarization, it typically occurs at low temperatures and in complex materials. In the simple oxide, the magnetoelectric antiferromagnet Cr$_2$O$_3$, we experimentally demonstrate the existence of specific domain walls that act as room-temperature multiferroic regions. This behavior stems from an anisotropic crystal-symmetry-dependent mechanism of exchange origin, which is applicable to a broad class of bipartite antiferromagnets. The key signature is the magnetization occurring at antiferromagnetic textures, driven by the flexo-Zeeman interaction. These findings establish a foundation for exploring high-temperature spin-driven multiferroicity for magnetoelectric spin-orbit memory and logic applications.
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All authors Paulina J. Prusik, Igor Veremchuk, Florin Radu, Andrey N. Anisimov, Pavlo Makushko, Georgy V. Astakhov, René Hübner, Alexander Edström, Jürgen Fassbender, Fabian Ganss, Massimiliano Stengel, Kirill D. Belashchenko, Denys Makarov, Oleksandr V. Pylypovskyi

Materials Science

Curvature-driven revival of charge density waves in non-Euclidean space

Zhipeng Song, Zeyu Liu, Junde Liu et al. (+12 more)

Strongly correlated quantum states, such as charge density waves (CDWs), are exquisitely sensitive to Fermi surface topology and lattice symmetry, and are typically quenched by heavy carrier doping. In two-dimensional (2D) systems, however, macroscopic geometric curvature emerges as a novel structural degree of freedom to modulate microscopic quantum coherence. This raises a compelling physical question: can non-Euclidean geometric deformations compete with extreme electronic perturbations to reshape, or even revive, a quenched macroscopic quantum order? Here, by constructing monolayer TiSe$_2$-NbSe$_2$ heterostructure on a BLG/SiC substrate for the first time, we report the curvature-driven revival of a frustrated charge order in a non-Euclidean space. Low-temperature angle-resolved photoemission spectroscopy (ARPES) reveals a massive interfacial charge transfer, which destroys the global Fermi surface nesting and completely suppresses the long-range CDW order in Euclidean flat regions. Strikingly, high-resolution scanning tunneling microscopy (STM) reveals that a novel, non-linear CDW state miraculously survives, remaining strictly localized within morphologically distorted, non-Euclidean nanoscale curved regions. Atomistic simulations unravel the structural origin of this phenomenon, demonstrating that interfacial twist and lattice mismatch spontaneously generate a corrugated superlattice.
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All authors Zhipeng Song, Zeyu Liu, Junde Liu, Yi Biao, Anning Yang, Qian Fang, Mojun Pan, Chen Liu, Jiaou Wang, Tian Qian, Chenmin shen, Hongliang Lu, Wei Ji, Hong-Jun Gao, Xiao Lin