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Physics Condensed Matter Materials Science

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Wednesday 3 December

Materials Science

Poly- and single-crystalline diamond nitrogen-induced TLS losses estimation with superconducting lumped elements micro-resonators

Francesco Mazzocchi, Martin Neidig, Hideaki Yamada et al. (+3 more)

Research on diamond has intensified due to its exceptional thermal, optical, and mechanical properties, making it a key material in quantum technologies and high-power applications. Diamonds with engineered nitrogen-vacancy (NV) centers represent a very sensitive platform for quantum sensing, while high-optical quality diamond windows represent a fundamental safety component inside Electron Cyclotron Resonance Heating (ECRH) systems in nuclear fusion reactors. A major challenge is the development of ultra-low-loss, high-optical-quality single-crystal diamond substrates to meet growing demands for quantum coherence and power handling. Traditionally, dielectric losses ($\tan \delta$) in diamonds are evaluated using Fabry-Perot microwave resonators, in which the resonance quality factors Q of the cavity with and without the sample are compared. These devices are limited to resolutions around 10$^{-5}$ by the need to keep the resonator dimensions within a reasonable range. In contrast, superconducting thin-film micro-strip resonators, with Q factors exceeding 10$^6$, are stated to provide higher sensitivity for assessing ultra-low-loss materials. This study examines four diamond samples grown through different processes, analyzing their dielectric losses at extreme low temperatures (sub-Kelvin) within the Two-Level System (TLS) framework. Complementary Raman spectroscopy measurements allowed us not only to associate higher nitrogen content with increased losses, but also to investigate how the different growth process influence the way these defects are incorporated in the crystal lattice.
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All authors Francesco Mazzocchi, Martin Neidig, Hideaki Yamada, Sebastian Kempf, Dirk Strauss, Theo Scherer

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

Real-Time Coupled Electron-Nuclear Dynamics of Chemical Bond Formation: Hydrogen Scattering from a Semiconductor Surface

Jialong Shi, Lingjun Zhu, Florian Nitz et al. (+4 more)

A first-principles coupled electron-nuclear dynamics simulation based on real-time, time-dependent density functional theory and Ehrenfest dynamics quantitatively repro-duces bimodal translational energy loss and angular distributions observed in experiment for hydrogen atom scattering from Ge(111)-c(2*8). The theory elucidates a site-selective mechanism of electronically nonadiabatic energy transfer associated with the formation of different Ge-H bonds. When a hydrogen atom approaches a Ge rest-atom, it is strongly accelerated toward the potential minimum forming a transient Ge-H bond and then re-flected by the repulsive wall. This transient bond formation triggers an ultrafast electron transfer event from the rest-atom to an adjacent Ge-adatom, involving several crossings between valence and conduction bands of the substrate. Electronic equilibration is impos-sible within such a short time (Born-Oppenheimer failure) allowing the H-atom kinetic energy to be converted to inter-band electronic excitation of the substrate. H-atom colli-sions at other Ge atoms also form a transient bond but exhibit no electronic excitation, resulting in distinctly less efficient energy loss in scattered H-atoms. The nucle-ar-to-electronic energy transfer observed in this system reflects the electronic dynamics of covalent bond formation at a semiconductor surface, a mechanism that is quite distinct from previously identified nonadiabatic energy transfer mechanisms at metal surfaces mediated by electronic friction or transient negative ions.
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All authors Jialong Shi, Lingjun Zhu, Florian Nitz, Oliver Bünermann, Alec M. Wodtke, Hua Guo, Bin Jiang

Materials Science · Cross-listed from cs.LG

Universally Converging Representations of Matter Across Scientific Foundation Models

Sathya Edamadaka, Soojung Yang, Ju Li et al. (+1 more)

Machine learning models of vastly different modalities and architectures are being trained to predict the behavior of molecules, materials, and proteins. However, it remains unclear whether they learn similar internal representations of matter. Understanding their latent structure is essential for building scientific foundation models that generalize reliably beyond their training domains. Although representational convergence has been observed in language and vision, its counterpart in the sciences has not been systematically explored. Here, we show that representations learned by nearly sixty scientific models, spanning string-, graph-, 3D atomistic, and protein-based modalities, are highly aligned across a wide range of chemical systems. Models trained on different datasets have highly similar representations of small molecules, and machine learning interatomic potentials converge in representation space as they improve in performance, suggesting that foundation models learn a common underlying representation of physical reality. We then show two distinct regimes of scientific models: on inputs similar to those seen during training, high-performing models align closely and weak models diverge into local sub-optima in representation space; on vastly different structures from those seen during training, nearly all models collapse onto a low-information representation, indicating that today's models remain limited by training data and inductive bias and do not yet encode truly universal structure. Our findings establish representational alignment as a quantitative benchmark for foundation-level generality in scientific models. More broadly, our work can track the emergence of universal representations of matter as models scale, and for selecting and distilling models whose learned representations transfer best across modalities, domains of matter, and scientific tasks.
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All authors Sathya Edamadaka, Soojung Yang, Ju Li, Rafael Gómez-Bombarelli

Materials Science

Revealing Nanoscale Molecular Organization in Liquid Crystals via Cryogenic Atom Probe Tomography

Kuan Meng, Kang'an Wang, Sebastian Eich et al. (+5 more)

While liquid crystals (LCs) have been extensively studied, obtaining a comprehensive nanoscale picture of their molecular organization remains challenging, as conventional techniques face an intrinsic trade-off between spatial and chemical resolution. Here, cryogenic atom probe tomography (cryo-APT) is introduced as a new analytical approach for LC materials, using 4'-Pentyl-4-cyanobiphenyl (5CB) and 4'-Octyl-4-cyanobiphenyl (8CB) as representative model compounds. This was enabled by a tailored cryogenic focused ion beam (cryo-FIB) protocol optimized for small organic molecules. The method enables controlled field evaporation of both intact molecules and diagnostic fragments, achieving over 90% molecular retention while preserving four characteristic dissociation patterns. By spatially correlating these fragmentation profiles with the local electric field derived from the tip geometry, we reveal field-directed dissociation pathways of CB molecules. In parallel, the distribution of intact molecular ions enables nanoscale visualization of material structure: we resolve homogeneous mixing of 5CB and 8CB in the nematic phase and directly observe the sub-nanometer crystalline layering in a supercooled 8CB sample, with contrast to the surrounding amorphous matrix suggesting the presence of a solid-liquid interface. This work establishes cryo-APT as a new powerful analytical platform for LC research and reveals its broad potential for application in soft matter systems.
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All authors Kuan Meng, Kang'an Wang, Sebastian Eich, Pierre Nacke, Johanna R. Bruckner, Patrick Stender, Frank Giesselmann, Guido Schmitz

Materials Science

DEM Simulations of Spheres Flowing Through a Hopper: Validation of Beverloo Law

Leticia M. V. da Silva, Erlifas Moreira Rocha, Piter Gargarella et al. (+1 more)

This work presents a detailed investigation of the discharge behavior of spherical granular materials through a conical–cylindrical hopper using Discrete Element Method (DEM) simulations. The aim is to assess the applicability limits of the empirical Beverloo law. The system was modeled with a monodisperse particles whose mechanical properties correspond to the $Al_{95}Fe_2Cr_2Ti_1$ alloy, and interparticle contacts were described using the Hertz–Mindlin (no slip) model. The simulations systematically explored the influence of particle diameter ($d$) and bed height ($h$) on the resulting mass flow rate ($Q$). The results reveal the coexistence of transient and steady-state discharge regimes. Good agreement with the Beverloo scaling was observed for relatively small diameter ratios ($D/d = 10$) and sufficiently large bed heights, where the flow stabilizes rapidly. For larger $D/d$ ratios, the discharge rate decays exponentially, indicating a breakdown of the constant-hydrostatic-pressure assumption underlying the Beverloo model. A dimensionless criterion for the validity of the Beverloo law is proposed as $\Pi_h = h/D > 2$, or equivalently $N = h/d > 20$. The quantitative agreement between DEM simulations and experimental measurements for polydisperse particle size distributions further validates the computational model and demonstrates its predictive capability for granular discharge in confined geometries.
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All authors Leticia M. V. da Silva, Erlifas Moreira Rocha, Piter Gargarella, Pedro Augusto F. P. Moreira

Materials Science

Terahertz light driven coherent excitation of a zone-folded Raman-active phonon mode in the Spin-Ladder System $\alpha'$-NaV$_2$O$_5$

Flavio Giorgianni, Martina Romani, Pascal Puphal et al. (+5 more)

We investigate the out-of-equilibrium lattice dynamics in the spin-ladder system $\alpha'$-NaV$_2$O$_5$ using intense terahertz (THz) pump and near-infrared (NIR) probe spectroscopy. When quasi-single-cycle THz pulses interact with $\alpha'$-NaV$_2$O$_5$ in its low-temperature, dimerized charge-ordered phase, they induce coherent oscillations in the time domain at the zone-folded Raman-active phonon frequency of 1.85 THz. By combining pump-probe measurements with lattice dynamics modeling based on equation-of-motion approach, we propose that these oscillations arise from a nonlinear coupling between Raman-active and infrared (IR)-active phonon modes, with the latter being resonantly excited by the THz pulses. In contrast, excitation with NIR femtosecond laser pulses does not produce measurable vibrational dynamics, highlighting the unique potential of THz-driven, nonlinear light-matter interactions for the coherent and selective control of structural dynamics in quantum materials.
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All authors Flavio Giorgianni, Martina Romani, Pascal Puphal, Masahiko Isobe, Leonie Spitz, Mariangela Cestelli Guidi, Carlo Vicario, Mattia Udina

Materials Science

Tuning spin currents in collinear antiferromagnets and altermagnets

Sajjan Sheoran and Pratibha Dev

Spin current generation through non-relativistic spin splittings, found in uncompensated magnets and d-wave altermagnets, is desirable for low-power spintronics. Such spin currents, however, are symmetry forbidden in conventional collinear antiferromagnets and higher-order altermagnets. Using spin point group analysis, we demonstrate that finite spin currents can be induced in these materials via magnetoelectric, piezomagnetic, and piezomagnetoelectric-like couplings. We utilize electric fields, strain, and their combinations to drive symmetry-lowering phase transitions into uncompensated magnetic or d-wave altermagnetic states, thereby enabling finite spin conductivity in a broader class of magnetic materials. We further substantiate this framework using density functional theory and Boltzmann transport calculations on representative magnetic materials - KV2Se2O, RuF4 , Cr2O3 , FeS2 , and MnPSe3 - spanning these different cases. The charge-to-spin conversion ratio reaches up to almost 100% via uncompensated magnetism and about 40% via d-wave altermagnetism under realistic conditions, highlighting the effectiveness of this approach for efficient spin current generation.
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Materials Science

DHICA ion-modified melanin based porous Si solar cell

M. Semenenko, T. Yu. Obukhova, S. O. Kravchenko et al. (+8 more)

This work studies photosensitivity and current-voltage characteristics under illumination of water-soluble eumelanin films based on DHICA tetramers and hybrid eumelanin/porous Si photovoltaic cells aimed at optimizing their characteristics. By using DMSO to dissolve melanin containing protonated carboxyl groups and to remove ammonium cations, it became possible to significantly reduce the ionic component of conductivity, thus improved the electron transport. It was found out that dissolution in DMSO provides a denser {\pi}-{\pi} stacking of DHICA tetramers, which led to a significant improvement in the photovoltaic cell parameters. In particular, the efficiency increased from 0.023 % to 4.4 % and the series resistance decreased from 119 {\Omega} to 42.6 {\Omega}. Modeling demonstrated that high-temperature annealing, which causes decarboxylation, leads to a structural rearrangement of tetramers from a Christmas tree-like configuration to a "toothed helix". At this, one of the planes partially straightens. This emphasizes the critical importance of the morphology of the organic layer for photogeneration of carriers in a heterojunction.
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All authors M. Semenenko, T. Yu. Obukhova, S. O. Kravchenko, O. S. Pylypchuk, O. Yu. Ostapenko, T. O. Kuzmenko, M. V. Voitovych, S. Davidenko, Ye. S. Davidenko, S. S. Davidenko, A. Sarikov

Materials Science

Evaluation of Foundational Machine Learned Interatomic Potentials for Migration Barrier Predictions

Achinthya Krishna Bheemaguli, Penghao Xiao and Gopalakrishnan Sai Gautam

Fast, and accurate prediction of ionic migration barriers ($E_m$) is crucial for designing next-generation battery materials that combine high energy density with facile ion transport. Given the computational costs associated with estimating $E_m$ using conventional density functional theory (DFT) based nudged elastic band (NEB) calculations, we benchmark the accuracy in $E_m$ and geometry predictions of five foundational machine learned interatomic potentials (MLIPs), which can potentially accelerate predictions of ionic transport. Specifically, we assess the accuracy of MACE-MP-0, Orb-v3, SevenNet, CHGNet, and M3GNet models, coupled with the NEB framework, against DFT-NEB-calculated $E_m$ across a diverse set of battery-relevant chemistries and structures. Notably, MACE-MP-0 and Orb-v3 exhibit the lowest mean absolute errors in $E_m$ predictions across the entire dataset and over data points that are not outliers, respectively. Importantly, Orb-v3 and SevenNet classify `good' versus `bad' ionic conductors with an accuracy of $>$82%, based on a threshold $E_m$ of 500~meV, indicating their utility in high-throughput screening approaches. Notably, intermediate images generated by MACE-MP-0 and SevenNet provide better initial guesses relative to conventional interpolation techniques in $>$71% of structures, offering a practical route to accelerate subsequent DFT-NEB relaxations. Finally, we observe that accurate $E_m$ predictions by MLIPs are not correlated with accurate (local) geometry predictions. Our work establishes the use-cases, accuracies, and limitations of foundational MLIPs in estimating $E_m$ and should serve as a base for accelerating the discovery of novel ionic conductors for batteries and beyond.
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Materials Science

High Pressure and Compositionally Directed Route to a Hexagonal GeSn Alloy Class

George Serghiou, Hans Josef Reichmann, Gang Ji et al. (+4 more)

Despite their electronic dominance, cubic diamond structured Si and Ge, are optoelectronically deficient. Recent work indicates, however, that a volume-expanded hexagonal Ge modification can exhibit intensely sought, superior optoelectronic characteristics. If larger Sn could form a hexagonal solid solution with Ge, this would achieve this expansion. But this was not expected because Ge and Sn are unreactive at ambient conditions, Sn does not have an ambient hexagonal symmetry, and only cubic or tetragonal binary modifications could be prepared under any conditions including thin film processing. This state of affairs is categorically changed here by subjecting Ge and Sn to pressures of 9 and 10 GPa and temperatures up to 1500 K using large-volume press methods. Synchrotron angle-dispersive X-ray diffraction, precession electron diffraction and chemical analysis using electron microscopy reveal ambient pressure recovery of hexagonal 2H, 4H and 6H Ge-Sn solid solutions (P63/mmc). Formation of this new binary materials landscape is correlated with Sn uptake, with the hexagonal symmetry being accessible below 21 atom % Sn and the cubic diamond symmetry at or above this value. The findings form fertile routes to advanced materials, by in tandem creating reactivity with pressure and directing production of needed crystal symmetries with composition, as well as opportunity to tune properties based on crystal symmetry, composition, and stacking sequence for optoelectronic applications. PubMed Disclaimer
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All authors George Serghiou, Hans Josef Reichmann, Gang Ji, Laurence Nigay, Jonathan P. Wright, Daniel J. Frost, Gus Calder

Materials Science

Static and dynamic properties of the frustrated spin-1/2 depleted-kagome antiferromagnet Cu$_7$(TeO$_3$)$_2$(SO$_4$)$_2$(OH)$_6$

K. U. Akshay, Sebin J. Sebastian, Q.-P. Ding et al. (+2 more)

The structural and magnetic properties of the two-dimensional spin-$1/2$ depleted-kagome compound Cu$_7$(TeO$_3$)$_2$(SO$_4$)$_2$(OH)$_6$ are investigated using x-ray diffraction, magnetization, heat capacity, and $^1$H Nuclear Magnetic Resonance (NMR) measurements. From the analysis of magnetic susceptibility, we found a large Curie-Weiss temperature [$\theta_{\rm CW} = -50(2)$ K] and the co-existence of antiferromagnetic and ferromagnetic interactions. The value of $\theta_{\rm CW}$ gives an estimate of the average nearest-neighbour antiferromagnetic interaction of $J/k_{\rm B} \simeq 66$ K. The NMR relaxation rates ($1/T_1$ and $1/T_2$) exhibit a peak, providing evidence for a magnetic long-range order at $T^*\simeq 4$ K which appears to be canted antiferromagnetic type. Heat capacity also features a broad maximum at $T^*$ that moves towards higher temperatures with increasing magnetic field, reflecting defect induced Schottky anomaly. The frustration parameter $f_r = \lvert \theta_{\rm CW} \lvert/{T^{*}}\simeq 12.5$ renders the compound a highly frustrated low-dimensional magnet.
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All authors K. U. Akshay, Sebin J. Sebastian, Q.-P. Ding, Y. Furukawa, R. Nath

Materials Science

High Thermoelectric Performance via Stacking-Controlled Symmetry Breaking in Layered XZnBi (X = Rb, Cs) Zintl Materials

Aadil Fayaz Wani, Nirma Kumari, SuDong Park et al. (+1 more)

High thermoelectric efficiency requires high Seebeck coefficient, high electrical conductivity, and low thermal conductivity. However, strategies that suppress thermal conductivity often simultaneously degrade electrical conductivity, making effective electrical-thermal decoupling highly challenging. Here, we show that atomic-layer stacking order change in XZnBi (X = Rb, Cs) provides an efficient route to achieve such decoupling. Even though electronic transport coefficients and relaxation times remain largely insensitive to stacking order due to preserved Fermi-surface topology, the lattice thermal conductivity exhibits a strong stacking dependence, with AB stacking significantly suppressing it below 1 Wm$^{-1}$K$^{-1}$ at temperatures above 300 K. The stacking transition from AA to AB breaks structural symmetries. It increases the three-phonon phase space and available scattering channel, substantially suppressing phonon transport by about 50$\%$ in both materials. As a result, the AB-stacked phases yield high ZT values of 1.96 (1.69) in n-type CsZnBi (RbZnBi) at 900 K, which is about 40$\%$ (30$\%$) higher than AA stacking. These findings establish the XZnBi family as promising thermoelectric candidates and highlight stacking-order controlled phonon transport as a robust strategy for advancing thermoelectric material design.
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All authors Aadil Fayaz Wani, Nirma Kumari, SuDong Park, Byungki Ryu

Materials Science

Unconventional Magneto-Optical Effects in Altermagnets

Yongpan Li, Yichen Liu and Cheng-Cheng Liu

The ideal altermagnets are a class of collinear, crystal-symmetry-enforced fully compensated magnets with nonrelativistic spin-split bands, in which contributions from Berry curvature to magneto-optical effects (MOEs) are strictly forbidden by an effective time-reversal symmetry. Here we show that, in such systems, MOEs are exclusively induced by the quantum metric and, in realistic altermagnets, are typically dominated by it. We refer to Berry-curvature-induced MOEs as conventional MOEs and to quantum-metric-dominated MOEs as unconventional MOEs. We derive general formulas that incorporate both Berry curvature and quantum metric for unconventional MOEs in altermagnets, enabling a quantitative evaluation of their respective contributions. Through symmetry analysis, we prove that ideal altermagnets are constrained to exhibit only unconventional MOEs. Using the three-dimensional canonical altermagnet MnTe and the emerging two-dimensional bilayer twisted altermagnet CrSBr as illustrative examples, we demonstrate that unconventional MOEs are prevalent in altermagnets. Our results establish altermagnets as a natural platform for quantum-metric-driven optical phenomena, substantially broadening the scope of MOEs and providing concrete predictions that can be tested in future experimental studies.
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Materials Science · Cross-listed from physics.chem-ph

Zero-Waste Biorefinery: Pyrolysis of Fermentation Residues into Catalytic Biochar for Circular Biohydrogen Systems

Muhammad Shahzaib

This study presents a closed-loop biorefinery strategy that thermochemically upcycles fermentation residues (FRs) from photo-fermentative biohydrogen production (PFHP) into functional biochar catalysts, thereby enhancing the efficiency of the initial PFHP process. Four FRs derived from hydrothermal and ethylene glycol-pretreated corn stover were pyrolyzed at 700{\deg}C. Multi-model kinetic analyses revealed diffusion-controlled mechanisms with activation energies ranging from 157 to 278 kJ/mol, while thermodynamic profiling highlighted the influence of feedstock composition on reaction spontaneity and entropy. Pyrolysis effectively restored porosity compromised during fermentation, yielding biochar with tailored properties: microporous BC3 (185 m2/g) from oxygen-rich precursors and mesoporous BC4 (76.58 m2/g) from graphitized residues. When reintroduced into PFHP, BC3 maximized cumulative hydrogen yield (570 mL) via pH buffering, and BC4 achieved the highest production rate (14.91 mL/h) through electron shuttle mechanisms. The integrated process concurrently generated syngas, bio-oil, and catalytic biochar, enabling waste valorization, renewable energy output, and process enhancement within a circular bioeconomy framework.
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Materials Science

Origin of shallow n-type doping in AlN and Al-rich AlGaN

Yujie Liu, Sieun Chae and Emmanouil Kioupakis

Achieving efficient n-type doping in AlN, a representative ultrawide bandgap (UWBG) semiconductor, remains a longstanding challenge that limits its application in high-power electronics and deep-ultraviolet optoelectronics. Conventional dopants in AlN often introduce deep levels or form compensating complexes, leading to low free-carrier concentrations. In this work, we combine first-principles defect calculations with a structural search method tailored to explore metastable configurations to systematically investigate donor-type defects in AlN. Our results reveal that the aluminum interstitial ($Al_i$) can exhibit shallow-donor behavior in specific metastable configurations that were previously overlooked. This discovery expands the understanding of n-type dopability in AlN, and highlights the critical role of metastable defects in modulating electronic properties.
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Materials Science

Tetragonal Fe2O: the stable iron oxide at Earth's core conditions

Junjie Jiang, Zhen Zhang, Tongqi Wen et al. (+2 more)

The Fe-O system is fundamental to understanding the composition and properties of the Earth's core. Recent studies have suggested the possible existence of stable, iron-rich FenO compounds at around 215 GPa. Here, we performed crystal-structure searches and fully anharmonic free-energy calculations to investigate the Fe-FeO system under inner-core conditions. We identified Fe2O as a stable phase and constructed its high P-T phase diagram. Fe2O undergoes a hexagonal-to-tetragonal transition with increasing pressure and temperature. It remains thermodynamically stable against decomposition into Fe and FeO from 200 to 400 GPa and at high temperatures. Although oxygen has been considered nearly absent in the inner core due to its limited solubility, these results suggest that oxygen can, in fact, be incorporated into the solid inner core in the form of an Fe+Fe2O mixture, and can match PREM densities for 53 mol% Fe2O. Our work has the potential to lead to a significant revision of the current understanding of the core's structure and composition.
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All authors Junjie Jiang, Zhen Zhang, Tongqi Wen, Renata M. Wentzcovitch, Yang Sun

Materials Science

On the Accuracy of Atomic Resolution Electrostatic Measurements in 2D Materials

Rafael V. Ferreira, Sebastian Calderon V. and Paulo J. Ferreira

The use of differential phase contrast (DPC) in scanning transmission electron microscopy (STEM) has shown much promise for directly investigating the functional properties of a material system, leveraging the natural coupling between the electron probe and atomic-scale electric fields to map the electrostatic configuration within a sample. However, the high sensitivity of these measurements makes them particularly vulnerable to variations in both sample properties and the configuration of the instrument, stressing the need for robust methodologies to ensure more accurate analyses. In this work, the influence of key instrumental parameters - probe convergence angle, defocus and two-fold astigmatism - on atomic-resolution segmented-detector DPC-STEM measurements is evaluated through extensive image simulations. Results show that the limit of interpretability for a 21 mrad defocused probe is found at a magnitude of 4 nm, where electrostatic field magnitude can be underestimated by about 16 % in overfocus and just above 10 % in underfocus. Equivalent results for a 30 mrad probe demonstrate underestimated values around 30 % at overfocus and 20 % for underfocus, at a lower interpretability limit of 3 nm. Two-fold astigmatism introduces orientation dependent variations that surpass 40 % for magnitudes below 3 nm, but a reduction in sensitivity to the aberration is observed when oriented along detector-segment edges. Overall, the analysis confirms the sensitivity and usefulness of the scattergram-based method and underscores the importance of optimized instrumental alignment for accurate CoM based STEM imaging.
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Materials Science · Cross-listed from cond-mat.supr-con

Theoretical Description of Electronic Modulation and Superconducting Coherence

Jaehwahn Kim, Davis A. Rens, Waqas Khalid et al. (+1 more)

An electronic modulation can retain a substantial local amplitude while its translational coherence is limited by spatial disorder. Its coupling to superconductivity therefore cannot be characterized by a single modulation intensity. We develop a phenomenological formulation of a finite-wave-vector complex electronic envelope coupled to a charged superconducting field. Translation and gauge symmetries constrain the interaction terms, while amplitude, modulation-gradient and condensate-gradient couplings act on distinct responses. The resulting variational equations give uniform coexistence conditions, local stability criteria and phase-gradient coefficients. We define the helicity modulus by a boundary twist, distinguish phase-only from amplitude-weighted correlations, and give an explicit minimal spectral Hamiltonian illustrating how the electronic texture may enter momentum-resolved measurements. The proposed tests use distinct spatial, spectral and stiffness observables; none assumes that a tunnelling gap directly measures condensate amplitude. An explicit kernel expansion yields the leading displacement of the selected wave vector, while the thermodynamic twist response determines phase rigidity independently of charge intensity. The analytical relations and selected numerical responses distinguish amplitude, spatial organization and condensate rigidity within the specified coupled-field model.
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All authors Jaehwahn Kim, Davis A. Rens, Waqas Khalid, Hyunchul Kim

Materials Science

Generative Refinement:A New Paradigm for Determining Single Crystal Structures Directly from HKL Data

Wen-Lin Luo, Yi Yuan, Cheng-Hui Li et al. (+2 more)

Single-crystal X-ray diffraction (SC-XRD) is the gold standard technique to characterize crystal structures in solid state. Despite significant advances in automation for structure solution, the refinement stage still depends heavily on expert intervention and subjective judgment, limiting accessibility and scalability. Herein, we introduce RefrActor, an end-to-end deep learning framework that enables crystal structure determination directly from HKL data. By coupling a physics-informed reciprocal-space encoder (ReciEncoder) with a symmetry-aware diffusion-based generator (StruDiffuser), RefrActor produces fully refined atomic models without requiring initial structural guesses or manual input. Comprehensive evaluations on the GenRef-10k benchmark demonstrates that RefrActor achieves low R1-factors across diverse systems, including low-symmetry, light-atom, and heavy-atom crystals. Case studies further confirm that RefrActor can correctly resolve hydrogen positions, elemental assignments, and moderate disorder. This work establishes a new data-driven paradigm for autonomous crystallographic analysis, offering a foundation for fully automated, high-throughput crystal structure determination.
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All authors Wen-Lin Luo, Yi Yuan, Cheng-Hui Li, Yue Zhao, Jing-Lin Zuo

Materials Science

Anomalous Hall effect in an amorphous antiferromagnet with inverted hysteresis

Xiangning Du, Yuxiang Zhu and Na Chen

Stemming from antiferromagnetic coupling, exchange bias allows inverted hysteresis in a magnetic system. Such room temperature magnetic reversal has yet to be observed in an amorphous antiferromagnet. Furthermore, the impact of this exchange bias effect on its magnetoelectric transport behavior remains a mystery. Here we discovered a zero-field magnetization switching effect in an exchange-biased amorphous antiferromagnet with inverted magnetic hysteresis. This zero-field magnetic reversal was further evidenced by its inverted large anomalous Hall effect. Notably, this collective spin flipping at zero field can occur at room temperature or above room temperature, which may be associated with quantum interference effect due to thermal fluctuation enhanced disorder. Our experimental results offer a way to design room-temperature exchange-biased amorphous antiferromagnets with zero-field multi magnetic-states and large anomalous Hall effect, holding potential for low-power and high-density memory applications.
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Tuesday 2 December

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

Characterization of the soft behavior of nematic elastomers over a range of temperature and strain rates

Alice Kutsyy, Adeline Wihardja, Victoria Lee et al. (+1 more)

Nematic elastomers are a particular class of liquid crystal elastomers (LCEs) that exhibit both liquid-crystalline order and rubber (entropic) elasticity. This combination makes them stimuli-responsive soft materials with a number of unusual thermo-mechanical properties. They have been proposed for various applications, including soft robotics, enhanced adhesion, and impact resistance. This paper presents a new experimental setup and a comprehensive dataset characterizing the soft behavior of nematic elastomers over a range of temperatures and strain rates. We also fit the results to a recently developed model of nematic elastomers.
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All authors Alice Kutsyy, Adeline Wihardja, Victoria Lee, Kaushik Bhattacharya

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

Space-Charge-Limited van der Waals Spin Transistor

Thomas K. M. Graham, Yu-Xuan Wang, Niranjana Renjith Nair et al. (+5 more)

Integrating semiconducting and magnetic materials could combine transistor-like operation with nonvolatility and enable architectures such as logic-in-memory. Here, we employ correlated electrical transport and scanning nitrogen-vacancy (NV) center magnetic imaging to elucidate a spin transistor concept that amalgamates vertical and lateral hopping transport inside a 2D antiferromagnetic semiconductor, mechanistically distinct from vertical tunneling devices. Our device, based on a monolayer-bilayer junction in CrSBr, displays giant, gate-tunable magnetoresistance driven by the dual action of electrostatic doping on space-charge-limited lateral conduction and interlayer exchange coupling. Moreover, we visualize a field-trainable, layer-sharing effect that selects between coherent or domain-wall reversal at the spin-flip transition, enabling multilevel, memristive conductance states. Our layer-dependent space charge mechanism for convergent electrical and magnetic control opens opportunities to address limitations in contemporary computing.
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All authors Thomas K. M. Graham, Yu-Xuan Wang, Niranjana Renjith Nair, Kseniia Mosina, Kenji Watanabe, Takashi Taniguchi, Zdenek Sofer, Brian B. Zhou

Materials Science

Novel phases in the Fe-Si-O system at terapascal pressures

Nan Huang, Renata M. Wentzcovitch, Zepeng Wu et al. (+4 more)

The Fe-Si-O ternary system, central to modeling the interiors of terrestrial planets, remains poorly constrained at Terapascal (TPa) pressures characteristic of super-Earth mantles. Using a combination of crystal-structure prediction and ab initio calculations, we identify three ternary compounds stable near 1 TPa: P3 FeSiO4, P3 Fe4Si5O18, and P-3 FeSi2O6. The first two phases are thermodynamically stable at low temperatures, whereas P-3 FeSi2O6 becomes favored above approximately 2000 K. All three are metallic, paramagnetic, and adopt pseudo-binary arrangements derived from the FeO2 and SiO2 end-member structures. Their crystal structures emerge through substitutions of Fe for Si in Fe2P-type SiO2 or of Si for Fe in Pnma-type FeO2, the stable elemental oxides at ~1 TPa. This structural continuity suggests that Fe preferentially substitutes for Si in the canonical Mg-silicates expected at TPa pressures. Notably, these new pseudo-binaries accommodate Fe in six- and nine-fold coordination, in contrast to the eight-fold cubic coordination found in FeO at similar pressures. The thermodynamic conditions under which these phases form from FeO2 and SiO2 mixtures are clarified through quasi-harmonic free-energy calculations. These phases imply a fundamentally different pattern of Fe incorporation into Mg-silicates at TPa pressures compared with that inferred for Earth's mantle, i.e., mainly [Fe]Mg. Their stability may trigger silicate dissociation into oxides ((Mg,Fe)2(Si,Fe)O4 -> 2(Mg,Fe)O + (Si,Fe)O2) at pressures below ~3 TPa, as expected in the Mg-Si-O system, with the extent of dissociation governed by iron content.
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All authors Nan Huang, Renata M. Wentzcovitch, Zepeng Wu, Feng Zheng, Bingxin Wu, Yang Sun, Shunqing Wu

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

Curvature Potential Formulation for Thin Elastic Sheets

Yael Cohen, Animesh Pandey, Yafei Zhang et al. (+2 more)

Thin elastic sheets appear in systems ranging from graphene to biological membranes, where phenomena such as wrinkling, folding, and thermal fluctuations originate from geometric nonlinearities. These effects are treated within weakly nonlinear theories, such as the Foppl-von Karman equations, which require small slopes and fail when deflections become large even if strains remain small. We introduce a methodological progress via a geometric reformulation of thin-sheet elasticity based on a stress potential and a curvature potential. This formulation preserves the structure of the classical equations while extending their validity to nonlinear, multivalued configurations, and geometrically frustrated states. The framework provides a unified description of thin-sheet mechanics in regimes inaccessible to existing theories and opens new possibilities for the study of elastic membranes and two-dimensional materials.
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All authors Yael Cohen, Animesh Pandey, Yafei Zhang, Cy Maor, Michael Moshe

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

Analytical approach to the magneto-fluorescence of triplet excitons

Yan Sun and A.D. Chepelianskii

The fluorescence of triplet excitons and color-centers is strongly dependent on magnetic field that mixes the zero field spin eigenstates that determine the radiative recombination rates back into the singlet ground state through spin-orbit coupling. For films of molecules, and polycrystalline color-centers samples an average over molecular orientations has to be performed to model the magneto-fluorescence lineshapes. This limits our analytical understanding of the lineshapes and complicates the analysis of the fluorescence dependence on magnetic field. Here, we present a framework that allows to average over triplet molecular orientations analytically. Our approach provides very accurate numerical routines computing precisely the averages matrix elements that appear in magneto-fluorescence and semi-analytical approximations that can be used to model experimental traces.
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Materials Science

Digital-Alloy Bragg Mirrors in High-Q Microcavities for Polariton Lasing

V. A. Stolyarov, A. S. Kurdyubov, A. V. Trifonov et al. (+7 more)

We present an approach to the molecular-beam epitaxy of high-Q planar GaAs-based microcavities in which the AlGaAs high-index layers of the distributed Bragg reflectors (DBRs) are replaced by short-period GaAs/AlAs superlattices (digital alloys) with similar optical properties. This design enables a significant reduction of interface roughness, precise control of the quarter-wavelength optical thickness and the effective Al content, suppression of the propagation of structural defects, and efficient tuning of intrinsic absorption at the polariton emission wavelength via optimization of the superlattice parameters. Using this approach, we fabricate a microcavity with a low polariton-lasing threshold of approximately 570 W/cm$^2$ and a high experimental quality factor of about 5.4 x $10^4$. This value exceeds by almost a factor of two the theoretical estimate obtained within an equivalent ternary-alloy model. We demonstrate that accurate modeling of the stop-band characteristics and the Q factor requires incorporating the modified electronic density of states in the superlattice, including quantum-confinement and excitonic effects.
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All authors V. A. Stolyarov, A. S. Kurdyubov, A. V. Trifonov, M. Yu. Petrov, I. V. Ignatiev, V. A. Lovtcius, S. A. Eliseev, Yu. P. Efimov, M. S. Lozhkin, A. V. Kavokin

Materials Science

Computer Simulation of the Growth of a Metal-Organic Framework Proto-crystal at Constant Chemical Potential

Sahar Andarzi Gargari, Emilio Méndez and Rocio Semino

Designing metal-organic frameworks (MOFs) synthesis protocols is currently largely driven by trial-and-error, since we lack fundamental understanding of the molecular level mechanisms that underlie their self-assembly processes. Previous works have studied the nucleation of MOFs, but their growth has never been studied by means of computer simulations, which provide molecular level detail. In this work, we combine constant chemical potential simulations with a particle insertion method to model the growth of the ZIF-8 MOF at varying synthesis temperatures and concentrations of the reactants. Non-classical growth mechanisms triggered by oligomer attachments were detected, with a higher predominance in the most concentrated setups. The newly formed layers preserve the pore-like density profile of the seed crystal but contain defective sites characterized by the presence of 3, 5 and 7 membered rings, typical of amorphous phases. Compared to the amorphous intermediate species obtained at the nucleation part of the self-assembly process previously investigated in our group [Chem. Mater., doi: 10.1021/acs.chemmater.5c02028, 2025], larger-sized rings are more common in the grown layer. Moreover, these are favored by increasing reactant concentration and temperature, as is the degree of deviation with respect to the original crystal structure. We computed growth rates for the steady-state regime, and the non-linear tendency with respect to concentration leads us to hypothesize that in these conditions the growth is controlled by the adsorption rather than by the diffusion processes.
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Materials Science

Gaunt and Breit Two-electron contributions to Mean-field Transformations and Fine Structure Splitting

Luca Murg, Christopher Lane and Roxanne M. Tutchton

Materials utilized by novel energy systems are often studied using weakly correlated mean-field theories. However, if these systems incorporate heavy elements, relativistic effects must be included. Therefore a Kramers unrestricted Coupled Cluster with singles and doubles excitation formalism within a molecular mean-field Exact Two-Component framework (X2C-mmf) using a four-component Dirac-Hartree-Fock (DHF) reference state is presented. The exact X2C-mmf transformed normal-order Hamiltonian incorporates all one-electron and two-electron (2e) contributions from the Coulomb, Gaunt, and Breit operators and is used with the Equation of Motion method to calculate the excitation energies of the alkali group of elements. Using this framework, the effects of 2e Gaunt and Breit integrals are studied. Results demonstrate growing contributions from these integrals to the generated X2C-mmf mean-fields and electronic fine structure calculations with increasing atomic number. Overall, this paper outlines the method and effect of a higher level of accuracy within the X2C-mmf approach and lays the foundation for future theoretical development of relativistic calculations within this framework.
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Materials Science

Fermi-liquid behavior and characteristic temperature-dependent susceptibility in clean RuO$_2$ crystal

Shubhankar Paul, Atsutoshi Ikeda, Hisakazu Matsuki et al. (+6 more)

The magnetic nature of the altermagnet candidate RuO$_2$ remains under debate. It has been recently shown from quantum oscillations and angle-resolved photoemission spectroscopy (ARPES) that the high-quality RuO$_2$ bulk single crystal is a paramagnetic metal. Here we report the specific heat and magnetic susceptibility in ultra-clean RuO$_2$ single crystals with residual resistivity ratio up to 1200. The magnetic susceptibility increases with temperature and is phenomenologically fitted with an inclusion of $T\textrm{ln}(T/T_0)$ over a wide temperature range up to 400 K. In contrast, the energy dependence of the density of states and thermal activation of quasiparticles lead to a decrease with temperature. Such characteristic temperature dependence, similar to that observed in other $d$-electron metals, is attributable to an enhanced orbital contribution arising from lattice-expansion-induced changes in the band structure. The electronic specific heat, the magnetic susceptibility, and the $T^2$ coefficient in resistivity point to a weakly-correlated 3D Fermi-liquid state with a modest electron correlation, as supported by the Wilson and Kadowaki-Woods ratios.
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All authors Shubhankar Paul, Atsutoshi Ikeda, Hisakazu Matsuki, Giordano Mattoni, Jörg Schmalian, Kunihiko Yamauchi, Chanchal Sow, Shingo Yonezawa, Yoshiteru Maeno

Materials Science

Learning interpretable surface elasticity properties from bulk properties

Saaketh Desai, Prasad P. Iyer and Remi Dingreville

Surface elasticity is central to understanding the mechanics and stability of surfaces and interfaces. It is characterized by quantities such as surface tension, residual surface stress, and surface stiffness, however their analytical expressions are typically difficult to derive from atomistic data, and depend strongly on modeling choices. This work presents a neural network-based equation learner which combines customized activation functions and connection-based pruning to discover parsimonious, closed-form equations for surface elasticity from atomistic simulations. Applying the method to seven face centered cubic (FCC) metals, our equation learner uncovers interpretable equations that describe both low-Miller index and high-Miller index surface properties, capturing long-tail property distributions accurately. The discovered expressions are decoupled into two components: a universal, geometry-driven orientation function, and material-specific baseline coefficients. We find that lower-order properties such as surface tension are fundamentally geometry dependent, while higher-order properties such as surface stress and elasticity show more complex geometry and material dependence. We also relate material dependent coefficients to bulk properties, forming a clear map from bulk material properties to surface elasticity. Overall, this approach demonstrates that interpretable neurosymbolic machine learning can bridge the gap between atomistic simulations and physical laws, enabling the discovery of generalizable structure-property relationships for materials science phenomena such as surface elasticity.
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