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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Monday 7 September

Materials Science

Scalable machine learning framework for multiphase identification from powder X-ray diffraction

Xinyang Tong, Ethan Jin, Jiahan Xu et al. (+3 more)

X-ray diffraction (XRD) is the primary tool for identifying crystalline phases following synthesis, but automated phase identification remains challenging, particularly for multiphase samples with overlapping peaks and experimental artifacts. While deep-learning methods have been proposed to improve upon classical search-match algorithms, most formulate phase identification as a single closed-set classification problem, requiring one shared model to discriminate among all candidate phases. Here we introduce GALAXI, which instead decouples the identification task into independent one-versus-all binary classifiers that each specialize in recognizing a single phase. These pre-trained classifiers first narrow the search space to a small set of plausible phases, which are then evaluated through Rietveld refinement to identify the combination of phases that best explains the full diffraction pattern. On a curated set of experimental patterns, GALAXI identifies the correct phases with a micro-F1 score of 0.935, outperforming classical search-match and prior deep-learning models. The method remains robust to common experimental artifacts, including low impurity phase fractions, small crystallite size, peak shifts, sample displacement, and texture, and performs well when applied to time-resolved in-situ XRD data from solid-state reactions. Moreover, because the phase-specific models are independent, GALAXI can expand to large reference libraries without retraining existing models. This modular architecture enables us to train classifiers for 64,594 structures from the Crystallography Open Database and deploy them through a public web interface at https://galaxi-xrd.com.
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All authors Xinyang Tong, Ethan Jin, Jiahan Xu, Aditya Rao, Pengcen Jiang, Nathan J. Szymanski

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

Spin–orbit-enhanced correlation sensitivity and anomalous magnetic response in non-dimerized $4d^4$ ilmenite CdRuO$_3$

Yuya Haraguchi, Hayato Yatsuzuka and Hiroko Aruga Katori

We report the synthesis and physical properties of CdRuO$_3$, a nominal Ru$^{4+}$ $4d^4$ ilmenite with edge-sharing RuO$_6$ honeycomb layers. Powder X-ray diffraction establishes a crystallographically non-dimerized $R\bar{3}$ structure with equivalent Ru-Ru bonds and a strongly distorted RuO$_6$ environment. The compacted-pellet resistivity is nonmetallic but non-Arrhenius, while the heat capacity contains a finite residual linear term. Matched nonmagnetic calculations show that PBE+$U$ without spin-orbit coupling remains metallic or semimetallic up to $U_{\mathrm{eff}} = 3$ eV, whereas PBE+SOC+$U$ exhibits a strong $U_{\mathrm{eff}}$ dependence and opens a direct gap of approximately 55 meV at $\Gamma$ for $U_{\mathrm{eff}} = 2.5$ eV. Spin-orbit coupling therefore markedly enhances the correlation sensitivity of the non-cubic Ru $t_{2g}$ manifold. After subtraction of a dilute Curie-Weiss defect contribution, the susceptibility remains weakly nonmonotonic and is inconsistent with both an ordinary Pauli response and independent spin-only $S = 1$ moments. CdRuO$_3$ thus realizes the non-dimerized structural branch predicted for ruthenium ilmenites, but not a simple robust multiorbital metal.
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Materials Science

Human-agent discovery of reconfigurable in-plane ferroelectric superdomain control

Yu Liu, Boris Slautin, Ching-Che Lin et al. (+3 more)

Automated experimentation is most effective when the observables, available actions, and objective are defined before the experiment starts, as is the case for Bayesian optimization. However, in many exploratory experiments, the variables that describe the sample must be extracted from the data, new operations emerge during the experiments, and the instrument budget is too small to learn the problem by trials. Here we introduce the Scanning Probe Agentic Research Cycle (SPARC) framework, in which a coding agent and a human operator share one microscope, one notebook, and two persistent memory files. FINDINGS.md stores graded conclusions about the experiment, whereas PITFALLS.md records learned failure modes of analysis and instrument. We apply SPARC to reconfigure the in-plane superdomain direction of a (111)-oriented PbZr0.2Ti0.8O3 film. In an operator-supervised campaign, the agent reanalyzed earlier manual measurements and developed an oriented lattice of stationary bias pulses with alternating polarity to reconfigure the superdomain direction. In a subsequent agent-controlled campaign, PITFALLS.md entries were compiled into checks that validate a design before any write. The experiments showed that spatial polarity alternation, instead of the exact matching between the lattice and lamellar periods, determines directional selection. Combining a raster scan with a masked pulse lattice printed the letters UTK into the superdomain orientation. The campaign also identified practical requirements for agentic experimentation where physical verification of instrument execution, the conditions under which stored findings remain valid, validation of new observables on instrument data, and robust control protocols.
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All authors Yu Liu, Boris Slautin, Ching-Che Lin, Jaegyu Kim, Lane W. Martin, Sergei V. Kalinin

Sunday 6 September

Materials Science · Cross-listed from cs.SE

The Double Measurement Confound in Agent Benchmarks: De-Scaffolding, Ground-Truth Scoring, and Reliability Beyond the Mean

Yonghong Zhang, Shadi Motaali, Vu Phong Dinh et al. (+6 more)

Agent benchmarks are increasingly used to compare large language models (LLMs) and guide deployment decisions, yet benchmark scores are meaningful only if they measure model capability rather than properties of the evaluation pipeline. We identify a double measurement confound: execution-critical decisions are performed by a fixed scaffold instead of the model, while the scorer evaluates outputs using criteria that may not reflect task correctness. We unify these issues within a measurement-theoretic framework that characterizes when benchmark scores can be interpreted as evidence of model capability, and instantiate it with an audit-and-repair protocol that (i) transfers execution-critical decisions from the scaffold to the model, (ii) replaces shape-based evaluation with seeded ground-truth scoring, and (iii) reports reliability beyond the mean through worst-case and tail-risk metrics. Experiments on ComtradeBench show that the joint intervention transforms a nearly flat leaderboard into a reliability spectrum that distinguishes both average performance and robustness across seeds. Applying the audit to existing benchmarks further shows that scorer validity is benchmark-specific, whereas scaffold ownership is an uncontrolled axis wherever we probed it. Our results suggest that benchmark scores should be interpreted together with their scaffolding level, scoring criterion, and reliability profile, providing a practical framework for more valid evaluation of LLM agents.
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All authors Yonghong Zhang, Shadi Motaali, Vu Phong Dinh, Avin Piroutiniya, Jorge E. López de Vergara, Luis de Pedro, Ricardo Correia, Isabel M. Parra, Yong Xie

Materials Science

Magneto-spin-orbit graphene: Chern topology and photoinduced Hall response

Artem V. Tarasov and Alexander V. Eryzhenkov

Magneto-spin-orbit graphene can host Chern phases due to proximity interactions, but in realistic heterostructures these depend on substrate chemistry, local stacking registry and may be altered by buried-interface reconstruction. Investigation of these effects requires special efforts to take into account the long-range moire patterns that often arise for these heterostructures. We address this question using first-principles calculations and effective four-band models for four out-of-plane magnetized Gr/(Au, Pt)/(Co, Mn) heterostructures in commensurate (2 x 2) and moire (9 x 9) supercells where the latter include misfit dislocations for the Co-based interfaces. The commensurate cells overestimate charge transfer and exaggerate valley asymmetry, whereas moire averaging strongly reduces both effects while preserving sizable spin splittings. The Pt spacer mediates stronger proximity interactions than Au, while replacing Co by Mn substantially changes the balance of the effective exchange interactions in a spacer-dependent manner. Introduction of misfit dislocations into the Co-based structures is selective and tunes the Dirac gap in Gr/Au/Co or spin splittings in Gr/Pt/Co. Graphene in Gr/Pt/Co exhibits effective ferromagnetic Chern phase with C = 2 in all studied supercells. By contrast, the moire models of the other three compositions are ferrimagnetic and topologically trivial, with C = 0. Nevertheless, they exhibit helicity-dependent photoinduced Hall responses, which are strongly enhanced by misfit-dislocation reconstruction in Gr/Au/Co. This work demonstrates that moire-scale stacking controls the effective Chern phase and Hall conductivity, whereas buried-interface defects tune the photoinduced Hall response without changing the topology.
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Materials Science

A Novel Nb-Based Eutectic Superalloy with Exceptional Ultrahigh-Temperature Mechanical Properties

Ayeman M. Nahin, Alfredo Navarrete, Xiaokun Yang et al. (+2 more)

Refractory alloys operating above 1300 {\deg}C, beyond the limit of Ni-based superalloys, must balance high-temperature strength, thermal stability, low density, low cost, and room-temperature tensile ductility, a combination that existing refractory alloys have yet to achieve. Here we report a castable Nb-based eutectic superalloy, Nb-10Mo-9.5C (at. %, NMC-1), comprising a uniform lamellar structure of Nb-Mo solid solution and Nb2C carbide phases. NMC-1 achieves 0.2% yield strengths of ~300 MPa and ~200 MPa at 1300 {\deg}C and 1500 {\deg}C, respectively, among the highest reported for Nb-based alloys, with pronounced strain hardening, non-zero room-temperature tensile ductility, and no observed microstructural coarsening after 100 h at 1400 {\deg}C. Its low density (8.65 g/cc) and cost (~$85/kg) yield a specific-strength-per-cost merit index that far surpasses commercial Nb, Mo, Ta, and W alloys, establishing a new design paradigm for ultrahigh-temperature structural materials.
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All authors Ayeman M. Nahin, Alfredo Navarrete, Xiaokun Yang, Eric A. Lass, Mingwei Zhang

Materials Science

Collective Excitonic Structure Governs Anomalously Weak Thermal Optical Dephasing in Conjugated Polymers

Henry J. Kantrow, Elizabeth Gutiérrez-Meza, Eric R. Bittner et al. (+2 more)

Conjugated polymer aggregates exhibit optical decoherence in the presence of strong vibronic coupling and substantial diversity in chemical structure, solid-state organization, and excitonic character. Here, we use coherence-detected and population-detected two-dimensional electronic spectroscopies to examine the temperature dependence of the homogeneous optical linewidth across a series of semiconducting polymers. Despite substantial differences in molecular architecture and solid-state organization, all polymers studied exhibit remarkably weak thermal linewidth scaling over the measured temperature range. Comparison between complementary detection modalities further shows that, while this weak temperature dependence is obust, the absolute homogeneous linewidth depends on the measured observable. This behavior reflects the different ways in which coherence- and population-detected measurements project population relaxation and pure dephasing onto the spectroscopic response. These results establish the weak thermal scaling of optical decoherence across a diverse series of conjugated polymers and show that its experimental manifestation must be interpreted in the context of the detection observable.
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All authors Henry J. Kantrow, Elizabeth Gutiérrez-Meza, Eric R. Bittner, Hao Li, Carlos Silva-Acuña

Materials Science

Revealing the origin of ionic conduction in silver-iodide-doped silver phosphate glass

Jennifer Freedberg, Joseph Maduzia, Andias Santoso et al. (+3 more)

Fast ionic transport is a defining feature of many solid electrolytes, yet its microscopic origin is not fully understood. In the absence of microscopic insights, the development of next-generation solid-state batteries remains largely empirical. Most existing measurements access either the low-frequency transport response or the high-frequency bound polarization, yet the intermediate mesoscopic frequency regime is where ionic transport emerges. By varying the $\mathrm{AgI}$ concentration ($x$) and performing time-domain terahertz spectroscopy (TDTS) in a prototypical glassy electrolyte $\left(\mathrm{AgI}\right)_{x}\left(\mathrm{AgPO_3}\right)_{(1-x)}$, we reveal this intermediate frequency regime and identify a crossover from bound-current-dominated conduction to conductivity arising from short-range dispersive ionic transport. We find that bound polarization associated with the bond-bending motion of the $\mathrm{P{-}O^- -Ag^+}$ motif is present across compositions but is insufficient to produce ionic transport on its own. Transport emerges only when this polarization is embedded in a sufficiently soft $\mathrm{AgPO_3}$ glassy matrix and accompanied by a high carrier density. These ingredients together take the system from a vibrationally bound response to short-range dispersive motion.
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All authors Jennifer Freedberg, Joseph Maduzia, Andias Santoso, Ranveer Singh, Placid Ferreira, Fahad Mahmood

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

Electronic correlations and fluctuating lattice distortions in vanadium dioxide

Antonio Picano, Martin Eckstein and Francesco Grandi

Metal-insulator transitions in correlated materials are often accompanied by a change of crystal structure. They are commonly described within a coherent lattice approximation, which combines a correlated treatment of the electrons with a lattice represented by one or a few classical distortion coordinates fixed by minimizing an energy. The structural degrees of freedom then carry no entropy of their own, even though the partition of the transition entropy between electrons and lattice is often what decides the transition temperature. Here we develop a stochastic semiclassical extension of dynamical mean-field theory in which correlated electrons and fluctuating lattice distortions are evolved together, extending previous formulations from linear to nonlinear electron-phonon interactions and from a single to several coupled lattice modes. The resulting non-conservative Langevin equations have deterministic forces, damping, and correlated noise generated self-consistently by the interacting electronic subsystem. Applying the approach to a minimal two-orbital model containing the two symmetry-distinct distortions of the monoclinic phase of vanadium dioxide, we find that the two distortions melt at well separated temperatures, giving an insulating, an intermediate metallic, and a high-symmetry phase. The two transitions have different origins: the melting of the dimerization is driven by the coupling to the correlated electrons and is captured already within the coherent lattice approximation, whereas the restoration of the undistorted structure requires the entropy of the fluctuating lattice. Since the electronic subsystem is treated within nonequilibrium dynamical mean-field theory, the framework can be extended in future work to photoexcited systems with nonthermal electronic distributions.
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Materials Science

First-principles-based Prediction of Phase Fields: Part I. Binary and Ternary Refractory Alloys

Pravan Omprakash, Nicholas Crnkovich, John Cavin et al. (+3 more)

Multiple principal element alloys (MPEAs) exhibit complex phase equilibria involving multinary solid solutions and intermetallics, which makes it challenging to predict their temperature-composition phase diagrams. Their vast compositional space makes first principles methods prohibitively expensive, while CALPHAD is limited by scarce experimental data. Here, we present a computationally efficient framework to predict the solvus phase boundaries, and hence, phase fields, in refractory MPEAs composed of Cr, Hf, Mo, Nb, Ta, Ti, V, W, and Zr. The approach combines DFT calculated binary mixing enthalpies with sub regular solution models to construct phase diagrams without fitting higher order interactions, enabling efficient scaling across composition space. Validation against 36 binary and 15 ternary phase diagrams demonstrates good agreement, with both experimental results and CALPHAD calculations. We find that the prediction accuracy is enhanced by incorporating lattice dependent energetics through sub regular solution models and including temperature-dependent elemental phase transitions. The framework captures miscibility gaps, solid solution stability, and intermetallic formation, with predicted miscible temperatures typically within 300 K of experimental values. Overall, this work establishes a scalable, first principles based route for highthroughput prediction of phase diagrams in refractory MPEAs. A publicly accessible web interface has also been developed to allow interactive exploration of the predicted phase diagrams, available at https://raptor.engr.wustl.edu.
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All authors Pravan Omprakash, Nicholas Crnkovich, John Cavin, Nathan Curtis, Adrien Couet, Rohan Mishra

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

Superconductivity in a Bulk Moire Superlattice Material

Subham Naik, Paul Monson, Susanta Manna et al. (+7 more)

Moire materials provide a versatile platform realizing emergent electronic states arising from enhanced correlation due to flat bands. A variety of phenomena including superconductivity, low dimensional ferromagnetism, Mott insulating phase, and topological phenomena have been reported in such systems. To date, moire phenomena have been predominantly explored in artificially assembled low dimensional van der Waals structures, where relative twist and lattice alignment are controlled during device fabrication. Recently, intrinsically grown bulk moire crystals have emerged as a complementary materials platform, in which lattice mismatch between constituent layers generates a coherent moire superlattice throughout the bulk crystal. Here, we report the evidence of bulk superconductivity in single crystals of a recently reported bulk Moire material [Sr6TaS8]1+x[TaS2]8 at ambient pressure. The material exhibits a bulk superconducting transition at Tc = 2.5 K, evidenced consistently by electrical transport, magnetic susceptibility, and heat capacity measurements on single crystals. Structural characterization by X-ray diffraction and atomic resolution electron microscopy establishes the composite, incommensurate crystal structure and scanning tunnelling microscopy reveals a long-wavelength surface modulation due to the incommensurate structure. The observation of bulk superconductivity establishes superconductivity as an emergent phase in this intrinsically synthesized moire material and highlights bulk moire crystals as a promising platform for investigating correlated quantum phenomena beyond artificially assembled two-dimensional structures.
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All authors Subham Naik, Paul Monson, Susanta Manna, Prabuddhakant Mishra, Soumyojit Chatterjee, Sandip Kuila, Partha Pratim Jana, M. B. Sreedhara, Rahul Sharma, Gohil S. Thakur

Materials Science · Cross-listed from quant-ph

Solution-phase fluorination of nanodiamond: near-surface NV$^-$ activation and spin relaxation

Szabolcs Czene, Olga Krafcsik, Nikoletta Jegenyés et al. (+4 more)

Nanodiamonds hosting luminescent point defects, known as fluorescent nanodiamonds (FND), are a leading platform for quantum technology. The nitrogen-vacancy (NV) centre is the most intensively studied of these; its negatively charged state (NV$^-$) can serve as a qubit at room temperature, and its stability is governed by surface functional groups. We present two solution-phase fluorination routes for stabilising NV$^-$: direct C-F bond formation by decarboxylation with xenon difluoride via a radical mechanism, and the Balz-Schiemann reaction, which replaces surface amino groups with fluorine. The two routes were compared by infrared, X-ray photoelectron, energy-dispersive X-ray, Raman and photoluminescence spectroscopy. Both gave a high NV$^-$ fraction, up to $\sim$90% on average and approaching 100% in fluorine-rich regions, which to our knowledge is among the highest reported for surface-terminated nanodiamonds of this size and, in particular, for fluorine termination. Frequency-domain relaxometry shows that the fluorinated particles retain a long spin-lattice relaxation time, $733\pm56$ and $712\pm20$ $\mu$s for the XeF$_2$ and Balz-Schiemann routes, several times the values reported for commercial HPHT nanodiamonds, although shorter than the $1173\pm123$ $\mu$s of the as-received material. Charge-state stability and spin lifetime therefore do not improve together: fluorination activates near-surface NV$^-$ centres, which are the most exposed to surface noise but also the ones that dominate relaxometric sensing.
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All authors Szabolcs Czene, Olga Krafcsik, Nikoletta Jegenyés, Dávid Beke, László Péter, Vladimir Verkhovlyuk, Adam Gali

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

Three-Dimensional Fermiology and Thickness-Tuned Magnetotransport in Single-Crystalline Antimony Flakes

Mikhail Gaponov, Jicheng Wang, Liang Zha et al. (+1 more)

The extreme magnetoresistance of compensated semimetals is governed by both the Fermi-surface geometry and carrier relaxation, but these contributions are difficult to disentangle in finite-size structures. Here, we combine longitudinal and Hall magnetotransport measurements with temperature- and angle-dependent Shubnikov–de Haas oscillations in single-crystalline Sb flakes grown by chemical vapor deposition (CVD), with thicknesses ranging from 110 to 783 nm. As thickness increases, the non-saturating MR at 2 K and 14 T rises nearly 30-fold, reaching $7.13\times10^{5}\%$, while the primary frequency $F_{\alpha}$ remains approximately 99 T without any systematic shift. A joint three-channel analysis of $\rho_{xx}(B)$ and $\rho_{xy}(B)$ reveals that this evolution is driven by an increase in the mobility of a nearly compensated electron–hole pair, rather than by a reconstruction of the primary pockets. Angle-dependent measurements confirm the existence of a closed three-dimensional $\alpha$ pocket, and a reproducible high-frequency sector (335-377 T) is consistent with the electron $\beta$ orbit of the $L$-point pockets in bulk Sb. Together, the transport and quantum-oscillation results show that thickness tunes extreme MR through dimension-dependent scattering while preserving bulk-like fermiology.
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All authors Mikhail Gaponov, Jicheng Wang, Liang Zha, Rui Wu

Materials Science

Machine learning for the design and prediction of soft-magnetic electromagnetic shielding FeCo-based alloys in laser cladding

Luting Wang, Suiyuan Chen, Xiancheng Zhu et al. (+4 more)

Electromagnetic shielding materials play a pivotal role in both aerospace applications and daily life. However, their design and manufacturing still face persistent challenges. Machine learning demonstrates significant potential in accelerating material development and compositions optimization. Furthermore, laser additive manufacturing provides powerful technical support for fabricating multi-component, multifunctional electromagnetic shielding materials with tailored properties. In this study, the multiple machine learning strategies have been proposed, based on experimental derivation and soft magnetic material databases, to accelerate the design of multifunctional FeCo-based alloys for electromagnetic interference (EMI) shielding within an almost infinite compositional space. This work presents a novel approach for the rapid and automated discovery of multifunctional alloys with optimized EMI shielding effectiveness, as well as enhanced magnetic and electrical properties.
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All authors Luting Wang, Suiyuan Chen, Xiancheng Zhu, Zhiqing Fang, Mei Wang, Yifan Li, Lei Shen

Materials Science

$\beta-(Al_{0.19} Ga_{0.81})_2 O_3/Ga_2 O_3$ Modulation-Doped Field-Effect Transistors with $>$ 6 kV Breakdown

Julian Gervassi Saga, Joshua T Buontempo, Nabasindhu Das et al. (+3 more)

$\beta-(Al_{0.19} Ga_{0.81})_2 O_3/Ga_2 O_3$ modulation-doped field-effect transistors (MODFETs) incorporating a high-quality Al2O3 gate dielectric and SiNx passivation are demonstrated for high-voltage operation. The devices exhibited a maximum drain current of 54 mA/mm, an on-resistance of 149 Ohm.mm, a minimum subthreshold slope of 94 mV/dec, and an ION/IOFF ratio exceeding $10^8$. Three-terminal breakdown measurements performed in Flourinert demonstrated a breakdown voltage that increased with gate-drain spacing, reaching 6.6 kV for a device with LGD = 28 microns. The corresponding average lateral electric field approached 2.4 MV/cm, while a power figure of merit of 222 MW/cm2 was achieved. To the best of the authors knowledge, the demonstrated breakdown voltage represents the highest reported value for a $\beta-(Al_x Ga_{1-x})_2 O_3/Ga_2 O_3$ MODFET and highlights the potential of modulation-doped $\beta$-Ga2O3 heterostructures for next-generation multi-kV power devices.
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All authors Julian Gervassi Saga, Joshua T Buontempo, Nabasindhu Das, Advait Gilankar, Hari P Nair, Nidhin Kurian Kalarickal

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

Signatures of spin-wave dynamics in quasiparticle interference

Alireza Akbari and Peter Thalmeier

We investigate momentum-resolved quasiparticle interference (QPI) in a localized-itinerant antiferromagnet, where ordered local moments are exchange coupled to conduction electrons. Static antiferromagnetic order reconstructs the electronic bands, while one-magnon processes further dress the quasiparticles through a momentum- and frequency-dependent self-energy. Incorporating this dynamical renormalization directly into the Born impurity scattering, we find a characteristic crossover in the QPI spectrum. Below the lower magnon-emission edge, the modification is predominantly dispersive and governed by the real part of the self-energy, whereas above this scale its imaginary part produces pronounced broadening and redistribution of the scattering intensity. The dynamical response persists beyond the upper magnon energy and is strongly asymmetric in tunneling bias for a particle–hole-asymmetric band. These results show that Fourier-transform tunneling spectroscopy can distinguish static magnetic reconstruction from dynamical spin-wave renormalization.
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Materials Science

First-Principles Study of Magnetism, Electronic Structure, and Bonding in Nb-Mn-Ge Kagome Compounds

Wei-Shen Tee, Shiya Chen, Weiyi Xia et al. (+3 more)

In this work, we systematically investigate the magnetic ground states, electronic structures, and bonding characteristics of the computationally predicted stable NbMn6Ge6, NbMn6Ge5, and NbMn6Ge4 using first-principles calculations. Our results show that structurally stable NbMn6Ge6 has a collinear antiferromagnetic configuration, while the metastable rhombohedral NbMn6Ge5 and NbMn6Ge4 favor ferromagnetic ground states. Magnetic moments on Mn atoms are nearly localized, suggesting the applicability of a generalized spin Hamiltonian. Magnetic anisotropy in AFM NbMn6Ge6 and FM NbMn6Ge5 has uniaxial behavior, while FM NbMn6Ge4 has in-plane anisotropy. Charge density difference and electron localization function analyses further show charge redistribution and bonding features within the Mn-Ge Kagome network and between adjacent structural layers. Electronic structures near the Fermi level show no features suitable for topological magnetism studies. Experimental synthesis, structural characterization, and magnetic measurements are required to verify our predictions.
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All authors Wei-Shen Tee, Shiya Chen, Weiyi Xia, Peter Minch, Cai-Zhuang Wang, Vladimir Antropov

Materials Science

Barrierless Water Dissociation on Rare-Earth Sesquioxide Surfaces from First Principles

Shuxiang Zhou, Jay A. LaVerne and Hanna Hlushko

Water dissociation on metal oxide surfaces is a key elementary step in heterogeneous catalysis, photocatalysis, and radiation chemistry, yet its mechanistic details on rare-earth (RE) sesquioxides remain poorly understood. Here, we investigate water dissociation on the (110) surfaces of three cubic bixbyite oxides, Sc$_2$O$_3$, Y$_2$O$_3$, and Lu$_2$O$_3$, using molecular dynamics combining ab initio calculations with on-the-fly machine-learning force field acceleration. By sampling 25 independent trajectories per material, we obtain an unbiased picture of the reaction landscape inaccessible to conventional static calculations. Two distinct dissociation pathways are identified: a conventional proximal mechanism with a small but finite barrier of $\sim$0.1 eV, and a previously unreported distal mechanism that is effectively barrierless and energetically preferred at both the adsorption and dissociation stages. The low barriers are consistent with the periodic array of inherently undercoordinated RE$^{3+}$ sites in the bixbyite lattice, suggesting that ordered intrinsic coordination defects play a role analogous to stochastic oxygen vacancies in conventional oxides.
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Materials Science

First Principles Thermodynamics of Zr B Segregation at Grain Boundaries in Recycled Nd2Fe14B

Avik Mahata and Miha Zakotnik

Grain-boundary chemistry is central to the coercivity and thermal stability of Nd2Fe14B permanent magnets, particularly in recycled magnets where recovery of the hard-magnetic phase does not by itself restore the intergranular microstructure. Our recent experimental study showed that nanoscale ZrB2 precipitates can emerge at grain boundaries and triple junctions during recycling despite an overall Zr concentration of only about 0.1 at.%, where they are associated with boundary stabilization and suppression of grain coarsening. Here we use spin-polarized density-functional theory with a Hubbard correction (DFT+U) to determine the atomistic thermodynamics underlying this preferential localization. A systematic set of composition-matched bulk/grain-boundary DFT+U supercells provides a common correlated-electron description across boundary chemistries. We compare B, Zr, Dy, and ZrB2-like local configurations in bulk and grain-boundary environments of Nd2Fe14B. Excess B is strongly stabilized at the boundary, while Zr also shows an independent thermodynamic preference for the interfacial region. When Zr and B are combined in a ZrB2-like configuration, the boundary preference is retained, indicating that the interface remains favorable as Zr-B coordination develops. These results establish a thermodynamic pathway for the co-localization of Zr and B prior to ZrB2 formation. Magnetic-state analysis further shows that all compared structures remain within the same high-moment Fe-sublattice regime, and boundary-localized defects generally perturb the normalized magnetization less than their matrix counterparts. The calculations therefore provide a first-principles explanation for why Zr-B chemistry concentrates at intergranular regions and how such boundary-localized states can support the microstructural stability required for high-coercivity recycled Nd-Fe-B magnets.
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Materials Science

Chemical and interface confinement effects in promoting plastic co-deformation in high-strength nano-scale eutectics

Arkajit Ghosh and Amit Misra

Eutectics offer a route to overcome plastic incompatibility in disparate-phase heterostructures by coupling microstructural refinement with phase-specific chemical and crystallographic hierarchy. Here, we investigate laser-rapid-solidified Al-(Si,Ge) eutectic composites designed along the univariant ternary eutectic path, solidifying with an Al-rich face-centered cubic (fcc) matrix and (Si,Ge)-rich diamond-cubic (dc) fibers as constituent eutectic phases with faceted interfaces. The microstructure was hierarchical in nature with finer structures within eutectic phases: nanoscale (Si,Ge) clusters in the Al phase and growth twins within the (Si,Ge) fibers with some Al retention. Although increasing Ge content coarsens the eutectic spacing, the yield strength is slightly enhanced compared to the relatively finer Al-Si, and tensile ductility of Al-(Si,Ge) is higher than that of Al-Si. In situ SEM micromechanical testing combined with post-mortem STEM and TEM showed that in the Al-rich phase, Ge segregated to the deformation-induced sub-grain boundaries that confined glide dislocations. Simultaneously, the (Si,Ge)-rich fibers remain crack-resistant at large plastic strain and exhibit deformation-induced planar faults, consistent with localized partial-dislocation activity at highly stressed interfaces and twin boundaries. These coupled mechanisms due to interface confinement and hard phase chemistry enable co-deformation of the metallic and covalent phases, providing a pathway for designing high-tensile-strength and ductile hierarchical eutectics beyond conventional length-scale-controlled strengthening.
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Saturday 5 September

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

Purely Electric-Field Control of Topological Magnetism in Two-Dimensional Magnets

Zhonglin He, Naafis Ahnaf Shahed, Kai Huang et al. (+2 more)

Electrical control of topological magnetism is central to realizing energy-efficient topological spintronics. Yet most electric-field approaches modify the competing magnetic interactions through a nonselective rearrangement of low-energy electronic states, yielding coarse magnetic phase control that often requires external magnetic fields to stabilize topological quasiparticles, while few schemes solely based on electric fields are restricted to specific conducting materials. Here, we establish a general approach for purely electric-field control of topological magnetism, in which an applied electric field electrostatically dopes a selected orbital-angular-momentum-polarized band edge of a two-dimensional (2D) van der Waals (vdW) magnetic semiconductor via proximity to an adjacent nonmagnetic vdW metal. We show that the resulting electrostatic doping predominantly tunes magnetic anisotropy of the 2D magnet, while leaving exchange interaction and Dzyaloshinskii-Moriya interaction nearly unchanged, thereby reversibly driving the system through ferromagnetic, skyrmion, spiral, and bimeron phases. We demonstrate this mechanism for CrBr3/graphene and Cr2Ge2Te6/TaS2 vdW heterostructures hosting electron and hole pockets of different orbital characters. These results establish a broadly applicable strategy for purely electric-field control in topological spintronics.
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All authors Zhonglin He, Naafis Ahnaf Shahed, Kai Huang, Himanshu Mavani, Evgeny Y. Tsymbal

Materials Science

Zonal dislocations in Laves phases: A coupled synchro-shear slip mechanism

Sang-Hyeok Lee, Mariano Forti, Thomas Hammerschmidt et al. (+6 more)

Synchro-shear is the primary plastic deformation mechanism in Laves phases at elevated temperatures, mediated by synchro-Shockley partial dislocations-zonal dislocations that proceed via localized events such as kink-pair nucleation and propagation. Using atomistic simulations, we identified a novel slip mechanism in Laves phases, namely coupled synchro-shear slip, involving the synchronized glide of two synchro-Shockley partial dislocations on adjacent slip planes, leading to the formation of extrinsic stacking faults. High-resolution scanning transmission electron microscopy revealed the extended core structures consistent with coupled synchro-Shockley partial dislocations bounded by extrinsic stacking faults in C15 NbCr2 and their involvement in twinning. These results highlight the critical role of coupled synchro-shear slip in enabling phase transformations between Laves polytypes and in governing twinning behavior, providing new atomistic insight into the kinetic nature of plasticity in topologically close-packed intermetallic phases.
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All authors Sang-Hyeok Lee, Mariano Forti, Thomas Hammerschmidt, Gang Liu, Julien Guénolé, Siyuan Zhang, Gerhard Dehm, Sandra Korte-Kerzel, Zhuocheng Xie

Materials Science

A Transport Framework for Evaluating Nanoscale Interconnect Materials

Md. Rafiqul Islam and Patrick E. Hopkins

As CMOS technology continues to scale, metallic interconnects increasingly limit circuit performance through rising resistivity, self-heating, and reliability degradation. Although several alternative metals have been proposed, a quantitative framework for evaluating their transport performance under nanoscale confinement remains unavailable. Here, we establish a transport framework by combining independently measured thermal and electrical conductivities with normalized and unnormalized transport figures of merit. We apply this framework to Cu, Ru, W, Co, Ir, and Mo thin films using new steady-state thermoreflectance measurements of Mo, Co, and Ir together with previously reported Cu, Ru, and W data. While Cu exhibits the highest intrinsic transport performance, its effective performance is substantially reduced by thickness scaling and Ta liner resistance. In contrast, Ru and Mo maintain favorable transport properties while enabling barrierless integration, identifying them as promising candidates for next-generation CMOS interconnects
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Materials Science

Altermagnetism from the viewpoint of chemistry

Nayana Devaraj, Anumita Bose, Md Afsar Reja et al. (+2 more)

Magnetism has been a central theme of research in chemistry, physics, and materials science, with chemical composition and bonding playing key roles in determining magnetic behavior. Altermagnets are a newly identified class of magnetic materials that combine features of conventional ferromagnets and antiferromagnets, arising from specific symmetry and electronic structure motifs. In this review, we present a chemistry-driven viewpoint on altermagnetism, highlighting how crystal chemistry, bonding, and electronic structure enable this unconventional magnetic order. We begin by introducing the fundamental concepts required to understand altermagnets, with an emphasis on symmetry considerations, orbital character, and electronic structure signatures. We then survey the diverse material families in which altermagnetism has been identified, drawing attention to coordination environments and structure-property relationships that favor altermagnetic order. We subsequently present experimental approaches which are useful for the characterization of altermagnetic materials. We examine ab initio materials discovery as a promising strategy for identifying new altermagnets, emphasizing how chemical constraints, such as symmetry and bonding, can guide computational searches. Other than their intrinsic importance, altermagnets provide interesting possibilities for technology. For this reason, we highlight possible applications that may be enabled through altermagnetic materials, along with their coupling with existing orders such as ferroelectricity and superconductivity. In conclusion, we point out some challenges and prospects, where chemically-based design guidelines can play an important role towards advancing altermagnetism research. In summary, this review offers an account of recent developments in altermagnetism, from basic concepts to the current state-of-the-art.
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All authors Nayana Devaraj, Anumita Bose, Md Afsar Reja, Arka Bandyopadhyay, Awadhesh Narayan

Materials Science · Cross-listed from cond-mat.stat-mech

Nanothermodynamics: stable thermal equilibrium and nanoscale fluctuations

Ralph V. Chamberlin

Nanothermodynamics describes the process where large systems subdivide into equilibrium distributions of small subsystems. A key ingredient is Hill's subdivision potential (E) that ensures adherence to the 1st and 2nd laws of thermodynamics in systems of any size. In this review and reassessment, it is emphasized that nanothermodynamics gives new insight into many measurements, theories, and simulations. Measurements establishing the need for nanothermodynamics show thermodynamic heterogeneity from multiple effective temperatures (T_i) inside most types of materials. One theoretical result that requires E=0 is the stable solution of Ising's original model for finite chains of interacting spins, a solution Ising could not have found 40 years before Hill's work. Another result is a novel solution to Gibbs' paradox that makes the entropy of the semiclassical ideal gas exactly extensive. Molecular dynamics simulations reveal how a standard fluctuation relation is modified when local degrees of freedom fluctuate faster than their coupling to the heat bath, consistent with the measured thermodynamic heterogeneity. Simulations of a Creutz-like model, comprised of Ising spins coupled to an explicit heat bath of Einstein oscillators, are used to study the 2nd law. It is found that maximizing the total entropy (S_t) requires an intrinsically irreversible step, providing a counterexample to the usual claim that statistical mechanics emerges from reversible dynamics. Furthermore, fluctuations of this model are best described by Einstein's reversal of Boltzmann's relation and the 2nd-law, not by recent fluctuation theorems.
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Materials Science · Cross-listed from physics.optics

Helicity-engineered nonlinear optical responses in photo-excited topological semimetals

Roshan Kumar Thakur, Prachi Venkat, Amar Bharti et al. (+1 more)

Topological materials provide a transformative arena for light-driven control of electronic motion; yet, direct manipulation of electron dynamics on sub-cycle timescale remains a significant challenge. We demonstrate that the strong-field-driven high-harmonic generation of a Weyl semimetal can be controlled and manipulated through bicircular pump-probe driving fields. While a lone probe pulse generates exclusively odd-order harmonics, the addition of a pump pulse triggers a series of sidebands arising from nonlinear frequency mixing of pump and probe photons. Our results reveal that the sideband intensities are highly sensitive to the relative helicity of the pulses and the orientation of the polarization plane. This sensitivity stems from the chiral nature of the Weyl nodes, which couples efficiently to the light's helicity only when the node-separation axis is perpendicular to the polarization plane. Furthermore, the significant suppression of sideband intensity with increasing pump-probe delay identifies these features as a potential clock for electron-hole decoherence. These findings establish frequency-mixed high-harmonic generation as a sensitive probe of chiral quantum dynamics and suggest a robust framework for manipulating topological currents via structured light, with implications for lightwave electronics and ultrafast quantum information processing.
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All authors Roshan Kumar Thakur, Prachi Venkat, Amar Bharti, Gopal Dixit

Materials Science

Momentum-Resolved Electronic Structure for Quasicrystals: Full-Band Spectra and Chern Number

Donglin Yang, Huajie Chen, Dexuan Zhou et al. (+1 more)

Quasicrystals lack the translational symmetry that underlies Bloch decomposition and Brillouin-zone integration, making full-band momentum-resolved electronic structure difficult to formulate and compute. We develop a systematically convergent reciprocal-space tight-binding framework for a broad class of quasicrystals. The method combines two systematically refinable components: a Fourier-module scattering-channel Hamiltonian that yields local spectral and current-current correlation quantities at each physical momentum, and an expanding hierarchy of pseudo-Brillouin zones that converts the resulting local quantities into bulk thermodynamic observables through an exact local-to-global relation. Applied to the Penrose and Ammann-Beenker models, the framework uncovers full-band momentum-resolved quasibands and a multichannel mechanism for pseudogap formation, both beyond the scope of low-energy effective models. It further resolves Zeeman-driven gap closings and reopenings, quantized Chern plateaus, and the phason invariance of bulk spectral and topological observables. This framework provides a unified reciprocal-space route to full-band spectral and topological properties of quasicrystals.
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All authors Donglin Yang, Huajie Chen, Dexuan Zhou, Xiaoxu Li

Materials Science

Elucidating Guest-Host Mechanisms in ZIF-L for Tuneable Highly Luminescent 2D Materials

Dylan A. Sherman, Lorenzo Donà, Cyril Besnard et al. (+6 more)

3D metal-organic frameworks (MOFs) are well known effective hosts for luminescent guests that improve tuneability, photostability and material fabricability. 2D guest@MOF systems, while less explored, offer competitive advantages over 3D guest@MOF systems due to their optical transparency, inter-layer spacing, and vertical thinness. This work examines luminescent organic dyes@ZIF-L to establish the underlying mechanisms of guest incorporation in ZIF-L and demonstrate the advantages of the 2D ZIF-L architecture for the material's functional luminescence. Analysing a case study system, fluorescein@ZIF-L (F@ZIF-L), using nanoscale FTIR, diffraction, and topology mapping, confirmed that fluorescein (F) resided in the ZIF-L framework cavities. Supported by surface energy simulations, the extent of guest incorporation was found to be indicated by a morphological continuum, from the characteristic leaf-shaped ZIF-L to rectangular F@ZIF-L. By modifying synthesis temperature and solvent ratios, the luminescent properties of F@ZIF-L could be rationally tuned in terms of guest loading (% mol) and arrangement (i.e. guest monomer to aggregate ratio). When optimised, F@ZIF-L exhibited tuneable emission chromaticity, 99.7% photoluminescent quantum yield, minimal guest leaching in solution over 12 months, and high photostability. Perylene@ZIF-L exhibited unique white light emitting properties, with CIE coordinates (0.33, 0.34) arising from a combination of yellow alpha-phase excimer and blue monomeric perylene emission. Finally, oriented luminescent thin films of guest@ZIF-L materials were grown on malleable Zn foils, demonstrating an in situ fabrication technique. Together, the work highlights the potential for luminescent dye@ZIF-L systems in developing tuneable and resilient luminescent components of next-generation optoelectronics, sensors, and lighting systems.
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All authors Dylan A. Sherman, Lorenzo Donà, Cyril Besnard, Lars Mester, Ben Slater, Judit Farrando-Pérez, Christopher Allen, Joaquín Silvestre-Albero, Jin-Chong Tan

Materials Science

Oxidation of Tantalum Nano-Film by Microwave Exposure

Massimiliano Zamengo, Lina Grineviciute, Hsin-Hui Huang et al. (+4 more)

Oxidation and ablation of 200 nm tantalum films were carried out by three routes: (i) femtosecond (fs-)laser direct write, (ii) high-temperature annealing (HTA) in a tube furnace, and (iii) annealing in a 2.45 GHz microwave cavity. Complete conversion of the 200 nm Ta layer into 409 nm of Ta2O5 required one hour at 600 C in the furnace, but only minutes at ~ 50 W of microwave power. Fs-laser (515 nm/200 fs) oxidation of the Ta nano-film set in at an average single-pulse fluence of ~ 0.1 J/cm2 under strong pulse-to-pulse overlap (900 pulses per focal spot), i.e. within a narrow window bounded from above by the onset of ablation. Under microwave annealing, both the cavity resonance frequency and the quality factor Q changed markedly at the metal-to-oxide transition, reflecting the collapse of the real and imaginary parts of the permittivity at 2.45 GHz. This dielectric contrast turns the cavity into a sensor: the oxidation can be followed in real time from the shift of the cavity resonance, providing a non-invasive, in-situ diagnostic tool.
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All authors Massimiliano Zamengo, Lina Grineviciute, Hsin-Hui Huang, Haoran Mu, Julianija Nikitina, Saulius Juodkazis, Junko Morikawa

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

In situ local learning of dynamic network materials

Shuaifeng Li and Xiaoming Mao

Functional materials realize functionalities through pre-designed structures, whereas physical neural networks are trained by prescribing input-output behavior. Unifying these views would allow materials to acquire functions directly from dynamical tasks. Here we introduce an in situ local learning framework for dynamic network materials. A forward drive and a time-reversed adjoint error drive are applied to the same mechanical network, enabling the material to compute gradients of a time-domain loss through its own dynamics. The resulting update rules are local, compatible with the principle of physical learning. Each bond or node requires only co-located forward and adjoint fields. The method trains spring constants, nodal masses, bond damping coefficients and nodal damping coefficients, and programs dynamical functions including broadband wave cloaking, evanescent-wave imaging, passive transient output enhancement and vowel classification. These examples involve distinct physical mechanisms, such as wave scattering, near-field information transfer, dissipative non-normal dynamics and machine learning, but are obtained by simply changing the loss function, rather than leveraging expert knowledge. Therefore, dynamic network materials can act both as programmable matter and as physical neural networks, providing a route to material systems that learn temporal responses in situ.
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