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Physics Condensed Matter Materials Science

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Friday 7 August

Materials Science · Cross-listed from quant-ph

Exploring the Relaxation Landscape of a 2D Quantum Magnet on a 256-Qubit Processor

Tiago Mendes-Santos, Joseph Vovrosh, Sergi Julià-Farré et al. (+33 more)

How quantum matter relaxes far from equilibrium is a central open problem in many-body physics, and one for which analog quantum simulators are well positioned to move from confirming theory to discovering new physics. Here, we use a two-dimensional Rydberg atom array of 256 qubits to map the relaxation landscape of the two-dimensional transverse-field Ising model across its phase diagram. Beyond the expected rapid thermalization, we identify two further regimes. The first is a prethermal regime whose dynamics are governed by an effective XY model. The second, and most unexpected, is a crossover regime characterized by a slowdown in relaxation. This slowdown occurs precisely where state-of-the-art classical tensor-network methods lose control at late times, whereas the quantum simulation remains consistent across system sizes. These results establish Rydberg atom arrays as a platform for scientific discovery in nonequilibrium quantum many-body dynamics.
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All authors Tiago Mendes-Santos, Joseph Vovrosh, Sergi Julià-Farré, Dorian Claveau, Guillaume Villaret, Lucas Béguin, Lucas Leclerc, Laurin Brunner, Wladislaw Krinitsin, Matthias Hecker, Fergus Hayes, Boris Albrecht, Lilian Bourachot, Clémence Briosne-Frejaville, Antoine Cornillot, Julius de Hond, Djibril Diallo, Clément Dupays, Robin Dupont, Thomas Eritzpokhoff, Loïc Henriet, Lucas Lassablière, Arvid Lindberg, Yohann Machu, Hadriel Mamann, Thomas Pansiot, Julien Ripoll, Bruno Ximenez, Henrique Silvério, Joseph Tindall, Markus Schmitt, Markus Heyl, Adrien Signoles, Constantin Dalyac, Antoine Browaeys, Alexandre Dauphin

Materials Science

Morphology Engineering of Mixed Ionic Electronic Conductors through Aqueous Phase Separation

Siqi Wang, Maria Restrepo, John Linkhorst et al. (+1 more)

The performance of organic electrochemical transistors (OECTs) is fundamentally governed by the interplay between ionic accessibility and electronic transport within organic mixed ionic-electronic conductors. Although increasing channel thickness enhances transconductance, it also prolongs ion transport, resulting in the well-known gain-speed trade-off. Here, we demonstrate that engineering the internal morphology of PEDOT:PSS:PEI films through pH-induced aqueous phase separation provides an effective route to mitigate this limitation. The resulting interconnected pore network promotes electrolyte penetration and increases the electrochemically addressable volume, while DMSO treatment and annealing enhance the continuity and ordering of the PEDOT-rich electronic phase. Consequently, porous OECT channels achieve a transconductance of 30 mS and a response time of 13 ms at an ultralow gate voltage of 0.05 V despite channel thicknesses exceeding 100 um. Comparison of films with comparable electronic conductivity but different pore architectures identifies morphology as the dominant factor governing device performance, supporting a transition from predominantly surface-limited modulation toward spatially distributed mixed ionic-electronic transport. Beyond demonstrating a scalable water-based fabrication strategy, this work establishes internal morphology as a design parameter that complements molecular structure and device geometry in organic mixed conductors, providing a general framework for the development of high-performance OECTs, soft bioelectronics, and future neuromorphic materials.
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All authors Siqi Wang, Maria Restrepo, John Linkhorst, Matthias Wessling

Materials Science · Cross-listed from quant-ph

Niobium Titanium Nitride as a High Tensile Stress Material for Nanomechanics

Korbinian Rubenbauer, Burak E. Bülbüloglu, Thomas Luschmann et al. (+6 more)

Over the past decades, high-coherence mechanical resonators have been continuously pushed to new limits, using techniques such as dissipation dilution and clamp-tapering to enhance their quality factor beyond intrinsic material limitations. Today, these mechanical resonators are often fabricated from silicon-nitride, silicon-carbide or aluminum. Recently, however, interest in novel material platforms has grown, especially those allowing for the integration within superconducting circuits. Among these, superconducting nitrides stand out as particularly promising due to their high transition temperatures compared to elementary superconductors. Here, we introduce them as nanomechanical resonators and report on the fabrication and characterization of highly stressed, doubly clamped niobium titanium nitride (NbTiN) nanostring resonators. Using optical interferometry, we determine the elastic properties and mechanical quality factor from room temperature to 13 K. We observe high tensile stress up to 0.81 GPa along with a Young's modulus of 181 GPa and an intrinsic mechanical quality factor up to 850. With these favorable mechanical properties, NbTiN constitutes a promising material platform for future applications in cavity electro- and nanomechanics.
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All authors Korbinian Rubenbauer, Burak E. Bülbüloglu, Thomas Luschmann, Manuel Müller, Stephan Geprägs, Witlef Wieczorek, Eva M. Weig, Matthias Althammer, Hans Huebl

Materials Science

Net and Hidden Spin-Valley Locking Enable Ultrahigh Hole Mobility in Covalent Bulk WN$_2$

Rong-Tian Pang, Zhongjuan Han, Jiayi Gong et al. (+3 more)

High carrier mobility at room temperature underpins high-performance electronics, yet high hole mobility remains rare in bulk semiconductors. Spin-valley locking can suppress intervalley scattering and enhance mobility, but it is limited to materials with broken inversion symmetry. Hidden spin polarization offers a possible route beyond this constraint, although whether its compensated spin textures could protect charge transport remains unclear. Using ab initio electron-phonon and transport calculations, we show that the two hexagonal phases of bulk WN$_2$ realize net and hidden spin-valley locking and exhibit ultrahigh room-temperature hole mobilities. In non-centrosymmetric $\alpha$-WN$_2$, a large valley spin splitting produces net spin-valley locking that nearly eliminates phonon-mediated intervalley scattering. In centrosymmetric $\beta$-WN$_2$, hidden Zeeman-type spin polarization yields a compensated, sector-resolved spin texture that reverses between valleys and suppresses intervalley scattering as effectively as the net locking does. The stiff W-N/N-N covalent network further keeps the remaining intravalley scattering weak. Our results establish hidden spin polarization as an effective transport-protection mechanism and extend spin-valley engineering to centrosymmetric bulk semiconductors.
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All authors Rong-Tian Pang, Zhongjuan Han, Jiayi Gong, Jiangang He, Jin-Jian Zhou, Yugui Yao

Materials Science

Local lattice dynamics of hcp zinc from EXAFS and machine-learning interatomic potentials

Vitalijs Dimitrijevs, Pjotrs Žguns, Inga Pudza et al. (+2 more)

The lattice dynamics of hexagonal close-packed (hcp) zinc, a prototypical anisotropic metal, is studied using temperature-dependent Zn K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy combined with atomistic simulations. The reverse Monte Carlo method enable the extraction of mean-square relative displacements (MSRDs) for eight coordination shells, providing a shell-resolved description of thermal motion. The MSRD temperature dependence, analysed using the correlated Einstein model, yields effective interatomic force constants and reveals pronounced anisotropy between in-plane and out-of-plane interactions. This anisotropy is further quantified by the ratio of MSRDs for the first and second coordination shells, which closely matches the anisotropic displacement parameters from diffraction experiments. Molecular dynamics simulations using the CHGNet universal machine-learning interatomic potential show that the original model overestimates thermal disorder, while a fine-tuned version substantially improves agreement with experimental EXAFS spectrum and radial distribution function. Overall, EXAFS-informed analysis is effective for validating and refining machine-learning interatomic potentials.
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All authors Vitalijs Dimitrijevs, Pjotrs Žguns, Inga Pudza, Aleksandr Kalinko, Alexei Kuzmin

Materials Science · Cross-listed from math-ph

Effective mass density for wave propagation in periodic layered media in the elasto-acoustic transition

Gabriel Núñez, William J. Parnell and Raphaël C. Assier

This article investigates the effective mass density for acoustic and elastic wave propagation in layered media, with emphasis on its transition between these regimes. Conventionally, it is possible to recover the governing equations of acoustics from those of elasticity via the no-shear limit. However, when considering an effective medium, the anisotropic effective mass density typically obtained for acoustics differs from the isotropic one found in elasticity. Furthermore, direct investigation of this limit is hindered by the fact that the effective mass density is independent of the shear modulus $\mu$. To tackle this problem, a transfer matrix approach is combined with Bloch's theorem to derive the effective wavenumber for a periodic material whose unit cell consists of two layers with different densities. The effective mass density is obtained analytically from the wavenumber, allowing for its evaluation in both regimes. Moreover, for the first time, a description of the transition from isotropic elastic to anisotropic acoustic effective density in a periodic layered medium is provided. Additionally, the existence of band structure in $\mu$-space is demonstrated, along with exceptional points, where compressional and shear modes coalesce and waves become evanescent, which heavily affects the behaviour of the effective density in the elasto-acoustic transition.
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Materials Science · Cross-listed from cond-mat.mes-hall

Magneto-optical signal from $\mathrm{Co_2Mn}$-based Heusler thin films in MOKE and BLS

Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher et al. (+3 more)

$\mathrm{Co_2Mn}$-based Heusler compounds offer a versatile, composition-tunable platform for magnonics and spintronics. Among them, the half-metallic $\mathrm{Co_2MnSi}$ is of particular interest for magnonics owing to its ultralow Gilbert damping, yet its weak magneto-optical response in the visible challenges optical probing such as Brillouin light scattering (BLS). We study the magneto-optical response of epitaxial $\mathrm{Co_2Mn}X$ films ($X = \{\mathrm{Al}_x\mathrm{Si}_{1-x}, \mathrm{Ga}_x\mathrm{Ge}_{1-x}, \mathrm{Sn}\}$) by magneto-optical Kerr effect (MOKE) spectroscopy and BLS. Angle-resolved MOKE resolves a significant, wavelength-dependent quadratic MOKE (QMOKE) only for $\mathrm{Co_2MnSi}$, whereas $\mathrm{Co_2MnAl}$, $\mathrm{Co_2MnGa}$ and $\mathrm{Co_2MnSn}$ respond dominantly linearly. Comparing BLS intensities of thermal magnons at two wavelengths, $\mathrm{Co_2MnSi}$ gives the weakest signal at 532 nm yet among the strongest at 457 nm, tracking the spectral dependence of its Kerr angle. These results emphasise the relation between the two magneto-optical techniques, guiding the choice of probing wavelength for $\mathrm{Co_2Mn}$-based Heusler compounds.
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All authors Anna Maria Friedel, Nicolas Fermon, Tobias Böttcher, Sébastien Petit-Watelot, Stéphane Andrieu, Philipp Pirro

Materials Science

Spin-group theory on Edelstein effect and spin-orbit torque in Collinear Ferromagnets

Yizhuo Song, Qing Zhang, Jiahao Shentu et al. (+2 more)

Current-induced spin-orbit torques (SOTs) are central to the electrical manipulation of magnetic order in spintronic devices. In transition-metal/collinear ferromagnet bilayers, field-like and damping-like torques have been described only phenomenologically via the spin or orbital Hall effect, lacking a rigorous symmetry-based foundation. The precise role of spin-orbit coupling (SOC) in both the Edelstein effect and SOTs has remained unresolved. Here we develop a spin-group symmetry theory for the Edelstein effect and SOTs in collinear ferromagnets, treating SOC as a symmetry-breaking perturbation. For 4mm (C4v) point group symmetry, we derive the full forms of field-like and damping-like torques, which arise predominantly from first- and second-order SOC. We further show that SOTs in both orbital-Hall-dominated Ti/Ni and spin-Hall-dominated Pt/CoFe bilayers originate at first-order SOC. Taking the 3m (C3v) torque as a paradigmatic example, we elucidate the role of second- and higher-order SOC torques in field-free switching of perpendicular magnetic anisotropy. Remarkably, in PtMnSb, we demonstrate that SOTs under certain point group symmetries deviate from the conventional form: zeroth- and first-order SOC contributions vanish identically, with the leading SOT emerging at second order. All symmetry-based predictions from spin-group theory are in excellent quantitative agreement with first-principles calculations. Our work establishes a unified symmetry framework for the microscopic understanding of the Edelstein effect and current-induced spin torques in ferromagnetic systems.
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All authors Yizhuo Song, Qing Zhang, Jiahao Shentu, Jie Li, Jia Zhang

Materials Science

Fast Isotropic Li-Ion Diffusion in Zeolitic Imidazolate Framework Glass Electrolytes for Batteries

Yong Li, Tao Du, Timothée Jamin et al. (+4 more)

All-solid-state lithium batteries require solid electrolytes that combine rapid room-temperature ion transport with mechanical robustness and interfacial compatibility. Zeolitic imidazolate framework (ZIF) glasses, with ZIFs being a sub-set of metal-organic frameworks, offer an attractive yet relatively underexplored platform because they combine an grainboundary-free and amorphous topology with chemically tunable frameworks. Here, we reveal that structural disorder unlocks fast and isotropic lithium diffusion in ZIF glasses. This is realized by using a machine learning interatomic potential to simulate Li+ transport in crystalline and glassy ZIF-4 and ZIF-62. Structural disorder reduces the activation energy for Li+ migration from ~0.35 eV to 0.16 eV and increases the extrapolated room-temperature diffusion coefficient by more than one order of magnitude for ZIF-4 and nearly sevenfold for ZIF-62. Analyses of non-Gaussian dynamics and van Hove correlation functions reveal that Li+ diffusion in crystalline ZIFs occurs via rare, dynamically heterogeneous hopping events among well-defined cages, whereas Li+ diffusion in glassy ZIFs is more homogeneous, continuous, and Fickian-like, benefiting from a wide distribution of coordination geometries and migration barriers. Li+ diffusion in crystalline ZIFs is strongly anisotropic, reflecting that ordered orientations of imidazolate and benzimidazolate rings impose distinct energy barriers along different crystallographic directions. Upon vitrification, these ring orientations become randomized, and hence, the diffusion of Li+ becomes isotropic or near-isotropic. These findings imply that well-designed metal-organic framework glasses are a promising candidate as high-performance solid-state electrolytes.
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All authors Yong Li, Tao Du, Timothée Jamin, Zhencai Li, Kasper Tolborg, Yuanzheng Yue, Morten M. Smedskjaer

Materials Science

Local Structure Dictates Ionic Transport and Mechanical Properties in Glassy Solid Electrolytes for Lithium Batteries

Yong Li, Tao Du, Rasmus Christensen et al. (+7 more)

Electrolytes composed of sulfide and halide glasses are promising candidates for all-solid-state lithium batteries owing to their processability, lack of grain boundaries, and relatively high ionic conductivity. Nevertheless, their ionic conductivity and mechanical properties are still not satisfying for the real-world applications. Significant advances in solid electrolytes require a thorough understanding of their microstructures. Here, we reveal the connections among structure, ionic transport properties, and mechanical stability in a series of glassy solid electrolytes by employing molecular dynamics simulations based on a machine learning interatomic potential. Specifically, we explore how the interplay between B-S and P-S networks in glassy Li-S-P-B-I (LSPBI) governs ionic conductivity and deformation behavior. The introduction of P2S5 into a B2S3-based glass induces a critical structural transformation, through which both ionic conductivity and mechanical nano-ductility can be enhanced. For a moderate P2S5 content, incorporated PS4 units depolymerize the rigid boron framework, creating percolative diffusion pathways for fast ionic transport. Concurrently, the flexible P-S-P configurations enable energy dissipation through bond bending, leading to the brittle-to-ductile transition. However, excessive P2S5 increases the fraction of polyphosphates (e.g., P2S6 and P2S7), thereby polymerizing the structural network and ultimately impeding Li+ mobility. Our work thus provides atomistic principles for engineering glass electrolytes with balanced ionic conductivity and mechanical robustness.
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All authors Yong Li, Tao Du, Rasmus Christensen, Timothée Jamin, Zhencai Li, Qi Zhang, Xiaoyi Xu, Kasper Tolborg, Yuanzheng Yue, Morten M. Smedskjaer

Materials Science

Autonomous Optimization of Complex Oxides for Thermochemical Fuel Production

Shuiping Gong, Mingcheng Li, Han Hao et al. (+13 more)

Two-step thermochemical fuel production, including H2O and CO2 splitting, offers a promising route to sustainable fuel manufacturing, with performance governed by redox-active oxides that enable cyclic reduction-oxidation reactions. Maximizing thermal-to-fuel conversion efficiency demands materials that simultaneously satisfy multiple stringent thermodynamic and kinetic targets. Addressing these requirements has increasingly driven materials design toward complex, multi-cation oxides, such as mixed-cation fluorites, perovskites, and high-entropy oxides, wherein composition, defect chemistry, phase stability, and morphology should be co-optimized. This creates a challenging materials optimization problem that is poorly suited to traditional trial-and-error approaches. In this review, we argue that thermochemical fuel production provides a compelling frontier for autonomous materials design and optimization. We first examine why redox-active complex oxides are difficult to develop, owing to multidimensional phase spaces, harsh operating conditions, and competing functional targets. We then discuss how high-throughput computation, automated synthesis, characterization and testing, and machine learning can be integrated into closed-loop workflows to address these challenges. Building on broader oxide materials research, we organize recent progress into a capability roadmap for complex-oxide optimization, spanning compositionally diverse synthesis, operando characterization, robotic testing, operation-condition computation, and multi-objective optimization. Finally, we outline key experimental, computational, and data challenges for building self-improving materials development platforms for materials development in thermochemical fuel production.
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All authors Shuiping Gong, Mingcheng Li, Han Hao, Zhenhao Zhou, Yi Li, Xiaobo Liao, Cheng Fang, Jian Deng, Jiangang He, Wenpei Gao, Yakun Yuan, Chris Wolverton, Tao Deng, Chaochao Dun, Runxia Cai, Zhenpeng Yao

Materials Science

Symmetry Classification of Non-Relativistic Hidden Spin Polarization in Noncollinear Magnets

Yuzhong Hu, Pan Zhou, Baoru Pan et al. (+2 more)

Hidden spin polarization (HSP), in which spin-polarized states exist locally while the total spin polarization are hidden in momentum space, has been extensively studied in nonmagnetic and collinear magnetic systems, but remains largely unexplored in noncollinear magnets. Here we establish a unified symmetry framework for HSP in noncollinear magnetic materials based on spin-group theory. We show that spin symmetries systematically constrain nonrelativistic spin polarization, giving rise to four distinct split spin-texture (SST) types for each local sector, denoted as SST-1, SST-2, SST-3, and SST-4. Based on these splitting forms, together with the dimensionality of the associated local spin textures and the symmetry relations between different local sectors, we further classify HSP into three categories: HSP-1, HSP-2, and HSP-3. We illustrate these categories using tight-binding models and representative material examples, including SrFe$_2$Se$_2$O, USb, Sr$_2$Mn$_3$Sb$_2$O$_2$, PrFeAsO, and GdMn$_2$Si$_2$. A survey of the MAGNDATA database further identifies 133, 7, and 139 candidate noncollinear magnetic materials hosting HSP-1, HSP-2, and HSP-3, respectively. In addition, our symmetry analysis and first-principles calculation show that many of these materials can exhibit nonzero spin-related response tensors. These results establish a general framework for understanding HSP in noncollinear magnets and highlight their potential for spin-dependent functionalities.
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All authors Yuzhong Hu, Pan Zhou, Baoru Pan, PengBo Lyu, Lizhong Sun

Materials Science

Optical Anisotropy and Phase Matching in Non-Centrosymmetric Perovskite Oxides from DFT+U and DFT+U+V Functionals

Mohamed S.M.M. Ali and Ismaila Dabo

Optical anisotropy underpins the operation and performance of a broad range of photonic and quantum technologies. In this work, we critically examine the accuracy of density functional theory approximations with onsite and intersite Hubbard corrections (the DFT+$U$ and DFT+$U$+$V$ functionals) in predicting the anisotropic optical response of the non-centrosymmetric perovskite oxides, such as BaTiO$_3$, LiNbO$_3$, KNbO$_3$, and PbTiO$_3$. It is found that correcting self-interaction errors using DFT+$U$ alone does not capture the optoelectronic response of these materials, often leading to a suppression of their optical anisotropy. While intersite Hubbard interactions restore this anisotropy, the choice of the (inter)atomic orbital manifold that defines the Hubbard correction remains critical to its accuracy. The predictive performance of the resulting, systematically validated DFT+$U$+$V$ functional is achieved at a fraction of the computational cost of hybrid functionals and many-body perturbation theory calculations. As benchmarks, we investigate Zn- and (Bi,Mn)-substituted BaTiO$_3$ solid solutions; the latter exhibit polarization-dependent bandgap narrowing from mid-gap states, substantially enhancing the dichroic ratio and birefringence with promising implications for polarization-sensitive photodetectors and integrated photonics.
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Materials Science · Cross-listed from cond-mat.str-el

Suppression of orbital ordering and emergence of a glassy magnetic state in a high-entropy spinel vanadate

Shun Ito, Sota Nakakuki, Satoshi Demura et al. (+1 more)

High-entropy oxides provide a unique platform for exploring the interplay between configurational disorder and correlated electronic states. We report on structural, thermodynamic, and magnetic properties of the high-entropy spinel vanadate (Li$_{0.2}$Mg$_{0.2}$Mn$_{0.2}$Co$_{0.2}$Zn$_{0.2}$)V$_2$O$_4$, in which orbital-active V ions occupy the pyrochlore sublattice. X-ray diffraction measurements reveal that the cubic spinel structure is preserved at temperatures down to 5 K without any detectable symmetry lowering. Unlike conventional spinel vanadates exhibiting a symmetry-lowering structural transition driven by orbital ordering, the compound that we study exhibits a suppression of long-range orbital ordering in the high-entropy state. Magnetic susceptibility measurements show glassy magnetic freezing at temperatures below $\sim$20 K, while specific-heat measurements reveal no anomaly associated with long-range ordering down to 3 K. Frequency-dependent ac susceptibility reveals pronounced glassy dynamics. Analyses based on the Mydosh parameter, dynamic scaling law, and Vogel–Fulcher law suggest an intermediate dynamical regime between canonical spin-glass and cluster-glass behavior. Furthermore, Cole–Cole analyses reveal systematic deviations from a single Debye relaxation process, indicating the presence of heterogeneous magnetic relaxation dynamics near the freezing regime. Our results demonstrate that, in a frustrated spinel vanadate, high configurational entropy suppresses long-range orbital ordering and stabilizes a heterogeneous glassy magnetic state, highlighting the combined roles of geometrical frustration, orbital degrees of freedom, and configurational disorder in high-entropy magnets.
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All authors Shun Ito, Sota Nakakuki, Satoshi Demura, Tadataka Watanabe

Materials Science

Giant-exchange-driven Vectorial Control of a Minimal Topological Magnet in Eu3In2As4

Haonan Chen, Xunkai Duan, Guangyi Wang et al. (+13 more)

The interplay between magnetism and band topology provides a route to controlling quantum states of matter, yet its realization in materials is often constrained by weak exchange coupling and complex electronic structures. Here, a giant exchange coupling is identified in the newly predicted topological magnet Eu3In2As4, giving rise to magnetization-dependent band shifts of up to 300 meV. Together with its intrinsically soft magnetic response, this strong cou-pling enables systematic tuning of topological phases by both the magnitude and orientation of applied magnetic fields. The magneto-topological phase diagram is mapped out in which an antiferromagnetic topological insulator ground state evolves, under modest fields, into a pro-posed intermediate 2/3-ferrimagnetic phase, and further into fully polarized ferromagnetic states predicted to host either Weyl or nodal-ring semimetals. Notably, the Weyl phase corresponds to a minimal model hosting a single pair of Weyl nodes. Quantum oscillations, anomalous Hall transport and magneto-infrared spectroscopy consistently reveal exchange-driven band recon-struction across these transitions. Rotation of the magnetization theoretically provides an effi-cient means to tune the momentum-space positions and separations of the Weyl nodes. These results establish Eu3In2As4 as a model system for exploring how strong exchange coupling can be used to control topological band structures with minimal complexity.
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All authors Haonan Chen, Xunkai Duan, Guangyi Wang, Yuhan Du, Huayao Li, Jiayu Wang, Wenbin Wu, Zixuan Xu, Yingchao Xia, Jiaming Gu, Pengliang Leng, Lin Miao, Fengfeng Zhu, Xiang Yuan, Tong Zhou, Cheng Zhang

Materials Science

Universal Magnetoresistance Scaling in Layered Pd-based Multiband Metals Beyond Compensated Semimetal Regime

Kenjiro Okawa and Takao Sasagawa

We systematically investigated the magnetoresistance ratio (MR) of single-crystalline, nonmagnetic layered Pd-based metals, including centrosymmetric PdTe2, PdPb2, and beta-PdBi2 and noncentrosymmetric alpha-PdBi. Our study identifies a distinct class of large MR in multiband, high-carrier-density systems. Unlike well-studied extremely large MR materials, such as Dirac and Weyl semimetals described by simple compensated-carrier models, these compounds possess complex Fermi surfaces, as validated by our first-principles calculations. Nevertheless, they exhibit a remarkably simple MR scaling governed by carrier mobility, manifested in systematic dependencies on magnetic field, temperature, and the residual resistivity ratio (RRR). The validity of Kohler's rule in high-RRR crystals indicates that MR is governed by a single effective scattering time, even in these multiband systems. The field and RRR dependences of MR follow an intermediate power-law behavior between linear and quadratic, attributable to imperfect carrier compensation and a distribution of carrier mobilities. Among the studied compounds, alpha-PdBi exhibits the largest MR, reaching 1500% (2 K, 7 T), owing to its exceptionally high RRR (approximately 660). However, when compared on an equal-RRR basis, its MR is smaller than that of its centrosymmetric counterparts. This trend suggests that additional scattering channels arising from spin-orbit-induced band splitting in noncentrosymmetric systems reduce the effective carrier mobility. Our results establish a new class of large MR in clean multiband metals where complex electronic structures give rise to emergent single-parameter scaling, highlighting the interplay between disorder, mobility, and symmetry.
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Materials Science · Cross-listed from physics.optics

Geometric Control of Visible Emitter Creation in Hexagonal Boron Nitride by Oblique Ion Irradiation

Sagar Chowdhury, Bhaveshkumar Kamaliya, Ramachandra Bangari et al. (+5 more)

Ion irradiation creates optically active defects in wide-bandgap van der Waals materials, yet most approaches tune defect formation by varying the ion species, energy, or fluence while leaving the incidence geometry fixed. The ion-incidence angle is established here as a geometric control parameter for engineering visible emitters in hexagonal boron nitride (hBN). The angle and ion fluence of a plasma-focused heavy-ion (Xe+) beam are varied across hBN flakes of different thickness, and the resulting photoluminescence is quantified. In thick flakes, oblique irradiation shifts the fluence for maximum emission by nearly two orders of magnitude relative to normal incidence, whereas thin flakes exhibit an angle-independent optimum. Ion-trajectory simulations attribute this thickness dependence to lateral redistribution of the collision cascade and enhanced oblique sputtering. Atomic force microscopy identifies distinct processing regimes that delineate the useful defect-creation window. Post-irradiation annealing quenches the emission and shifts the spectral weight toward the green-yellow band while preserving the angle-dependent activation trends. Spectrally resolved lifetime measurements show comparable biexponential dynamics for normal and oblique incidence, consistent with emission from related defect families rather than a geometry-specific emitter species. These results establish ion-incidence geometry as a materials-level knob for programming optical defect activation and spatial defect distributions in van der Waals photonic materials.
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All authors Sagar Chowdhury, Bhaveshkumar Kamaliya, Ramachandra Bangari, Caleb Whittier, Joseph Spielbauer, Nabil D. Bassim, Thomas G. Folland, Ravitej Uppu

Materials Science

Cross-Geometry Transferability Assessment of Universal Machine Learning Interatomic Potentials: From Bulk Materials to Atomic Nanowires

Pedro H. M. Zanineli, Bruno Focassio and Gabriel R. Schleder

Foundation machine-learning interatomic potentials (MLIPs) enable atomistic simulations at substantially lower computational cost than first-principles methods, but their reliability across structural geometries remains insufficiently understood. Here, we construct a density-functional-theory dataset of ZrO2 configurations spanning bulk, slab, particle, neck, and atomically thin wire environments motivated by an experimentally observed ZrO2 desintering process involving neck thinning and atomic wire formation. We first benchmark 26 pretrained MLIPs and observe pronounced geometry-dependent degradation in zero-shot predictions. Without any training, after only reference-energy alignment, the best zero-shot model (ORB-V3) reaches energy and force root-mean-square errors of 6 meV/atom and 197.3 meV/Å, respectively, with the largest force errors in neck and wire configurations. We then compare zero-shot inference, fine-tuning, and training from scratch strategies. Fine-tuning yields lower energy and force errors than training from scratch, while both require comparable wall-clock time. Geometry-specific fine-tuning improves in-domain accuracy but frequently produces negative transfer to other structural classes, whereas mixed-geometry fine-tuning reduces cross-geometry errors. Evaluations of elastic and vibrational properties, surface energies, and neck dynamics further show that rankings based on average energy and force errors do not universally predict property-level behavior. These results demonstrate that geometry-diverse target data and independent physical validations are necessary when adapting foundation MLIPs to low-coordination (ionic) nanostructures.
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Thursday 6 August

Materials Science

Extracting the full conductivity tensor in a rectangular sample

Julia Gelfond and Oskar Vafek

Electrical transport measurements reveal that many 2D materials exhibit anisotropic conductivity. However, current methodologies for rectangular geometries can only extract a partial conductivity tensor or are difficult to execute experimentally. Here, we propose a simple experimental procedure to extract the full conductivity tensor (or the resistivity tensor by inversion) including the principal axes angle. Our procedure is developed by using a conformal mapping approach to obtain an analytical expression for the potential with a point source and drain on the perimeter. Our solution agrees very well with numerical simulations using COMSOL and the known limiting case where the principal axes angle vanishes. Finite source/drains can be modeled using superposition.
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Materials Science

Nonreciprocity reversal of magnetoacoustic attenuation in NiFe alloy thin films

Mingran Xu, Kei Yamamoto, Kouta Kondou et al. (+8 more)

Nonreciprocity, the asymmetry of transport, underlies technologies from the diode to the microwave isolator. In a ferromagnet, a surface acoustic wave generates an elliptical effective field with propagation-locked handedness, breaking the reciprocity of its propagation. Despite decades of study on this phenomenon, a method for controlling the sign of the nonreciprocity has remained elusive. Here we observe a sign reversal in Ni$_x$Fe$_{100-x}$ films. A 0.8 at.% change across Permalloy's zero-magnetostriction composition, where the magnetoelastic coefficient $b$ changes sign, reverses the handedness of the elliptical effective field and thereby the nonreciprocity, from 78.6% to -61.8%. Angle-dependent measurements and spin-wave-ellipticity modelling show that reversing the sign of $b$ reverses the handedness of the elliptically polarized effective field. Aided by cubic frequency scaling, we resolve the sign of $b$ down to -0.05 MPa in a 10-nm film, establishing nonreciprocity as a nanoscale probe of magnetoelastic coupling.
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All authors Mingran Xu, Kei Yamamoto, Kouta Kondou, Zheng Zhu, Liyang Liao, Kiyohiro Adachi, Tomoka Kikitsu, Daisuke Hashizume, Dirk Grundler, Sadamichi Maekawa, Yoshichika Otani

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

Emergence of Bogoliubov Fermi Surfaces in hybrid Al/InAs heterostructures

S. Feyrer, V. Dimic, I. Lobato et al. (+15 more)

We investigate the microwave electrodynamics of a proximitized two-dimensional electron gas in hybrid superconductor/semiconductor heterostructures. Using lumped-element resonators with inductor wires oriented relative to an in-plane magnetic field, we directly probe the superfluid stiffness via the kinetic inductance. As the field increases, the resonance frequency exhibits a non-monotonic and strongly anisotropic evolution that cannot be explained by orbital pair breaking alone. We show that this behavior is consistent with the emergence of Bogoliubov Fermi surfaces, which selectively suppress the supercurrent response depending on the direction of the magnetic field. Microscopic calculations of the stiffness tensor capture the observed anisotropy driven by the interplay of Zeeman and orbital Fulde-Ferrell effects. Our results establish microwave stiffness measurements as a sensitive probe of anisotropic gapless superconductivity in hybrid systems.
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All authors S. Feyrer, V. Dimic, I. Lobato, A. Kirchner, P. Drexler, L. Rupp, D. Bougeard, T. Lindemann, S. Gronin, G. Gardner, M. J. Manfra, G. F. R. Ruiz, C. A. Balseiro, L. Arrachea, M. Aprili, N. Paradiso, C. Strunk, L. Tosi

Materials Science

Sublattice-resolved coherent phonon dynamics in charge density waves

Kyoung Hun Oh, Honglie Ning, Zongqi Shen et al. (+15 more)

Phonons govern fundamental material properties and play a central role in various electronic phase transitions. Coherent driving of specific phonon modes enables on-demand phase control, motivating sublattice-resolved identification of real-space phonon motions. Yet experimentally resolving these motions remains challenging, limiting precise phonon-based control. Here, we introduce a dynamical protocol to track element-resolved phonon dynamics in the charge density wave material EuTe4, in which the dominant Te-sublattice charge order is accompanied by a previously unreported Eu-sublattice component. We leverage the elemental selectivity of time-resolved resonant X-ray scattering to reveal three coherent phonon modes with distinct sublattice character, thereby disentangling Eu- and Te-dominated lattice dynamics, in good agreement with theoretical calculations of the phonon eigenvectors. This time-domain approach, which surpasses the energy-resolution limits of conventional frequency-domain inelastic scattering, provides a broadly applicable framework for decomposing coherent phonons in multi-element materials, which is crucial for the targeted control of phases of matter.
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All authors Kyoung Hun Oh, Honglie Ning, Zongqi Shen, Yifan Su, Jack Maier, Gyeongbo Kang, Hyeongi Choi, Dong Wu, Qiaomei Liu, Hyun-Woo J. Kim, Seunghyeok Ha, Jaehwon Kim, Byungjune Lee, B. J. Kim, N. L. Wang, Yao Wang, Hoyoung Jang, Nuh Gedik

Materials Science

Metal-Coordination Effects on the Stability and ORR/OER Activity of Layered Organometallic Single-Atom Catalysts: A Theoretical Study

Pedro H. Souza, Victor Hoyos-Sinchi and Walter Orellana

Organometallic layered materials have emerged as promising single-atom catalysts for oxygen reduction and evolution reactions, but their practical use has been limited by insufficient electrochemical stability. Here, we present a density functional theory study clarifying the relationship between catalytic activity and stability in organometallic single-atom catalysts with metal-N$_4$ (MN$_4$) and metal-O$_4$ (MO$_4$) coordination. We compare graphene-embedded MN$_4$ motif and phthalocyanine-like frameworks with MO$_4$-coordination frameworks, including M$_4$(OHPTP)$_2$ and M$_3$(HHTP)$_2$ (M = Mn, Fe, Co, Ni, Cu, Zn). Stability is assessed by surface Pourbaix analysis, while activity is evaluated using the computational hydrogen electrode method. MN$_4$ systems show competitive overpotentials but suffer strong pH-dependent instability. In contrast, MO$_4$ frameworks exhibit enhanced robustness across wide pH ranges while maintaining good catalytic performance. A proposed stability descriptor enables direct comparison across systems, identifying MO$_4$ coordination structures, particularly M$_4$(OHPTP)$_2$ (M = Zn, Co) as optimal for balancing activity and stability in practical electrocatalysis.
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Materials Science · Cross-listed from cond-mat.mes-hall

Unconventional Scaling of Electric Hall Effect in Magnetic Weyl Semimetals

Chaoxi Cui, Yilin Han, Run-Wu Zhang et al. (+2 more)

Electric Hall Effect (EHE), a unique phenomenon in two-dimensional (2D) magnetic systems, refers to the generation of Hall current by an out-of-plane electric field $\Ez$. Here, we demonstrate that for 2D magnetic Weyl semimetals that host doubly degenerate nodal points, the EHE features multiple unconventional scaling laws. At zero temperature, the EHE exhibits a topological $E_F^{-1}$ Fermi-energy scaling. Remarkably, the prefactor of the scaling is determined by the global topological charge of the point without any dependence on the local parameters of the system, leading to a universal and significant enhancement of Hall response in any species of Weyl points as the Fermi energy approaches the Weyl point. This significant response enables a weak electric field to be directly converted into a measurable Hall signal. Surprisingly, this enhanced Hall response is not diminished by temperature, but evolves into an unconventional logarithmically corrected scaling at finite temperature $\sigma_{xy}\propto\Ez\ln(1/|\Ez|)$ for weak $\Ez$, still yielding a divergent electric-field susceptibility. Thus, our work not only unveils intriguing scaling laws resulting from the interaction between magnetism and topology, but also suggests a novel scaling-enhanced and temperature-robust mechanism that may enable weak electric-field sensing through a practical and all-electric route.
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All authors Chaoxi Cui, Yilin Han, Run-Wu Zhang, Zhi-Ming Yu, Yugui Yao

Materials Science · Cross-listed from physics.optics

Pulse-Duration Control of Subcycle Multiband Electron Dynamics Extends the High-Harmonic Cutoff in a Light-Driven Insulator

Hortense Allegre, Simon V. B. Jensen, Joseph J. Broughton et al. (+7 more)

We demonstrate pathway-selective control of extreme-ultraviolet high-harmonic generation by jointly tuning laser pulse duration ($5$ - $29$ fs) and intensity ($0.8$ - $74$ TW/cm$^2$). Many-cycle pulses at moderate intensities, $\sim 6$ TW/cm$^2$, promote cumulative carrier transfer over successive optical cycles, progressively accessing higher conduction bands. In contrast, few-cycle, high-intensity, $\sim 22$ TW/cm$^2$, pulses drive subcycle multiband dynamics that reach $25$ - $50$ eV photon energies before decoherence can suppress coherent emission. These results reveal pulse duration and intensity as decisive control knobs for high-harmonic emission, opening a route to band-structure-guided pulse design for higher energy extreme-ultraviolet light sources.
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All authors Hortense Allegre, Simon V. B. Jensen, Joseph J. Broughton, Tim Klee, Yan Li, Jon P. Marangos, Nicolas Tancogne-Dejean, Angel Rubio, John W. G. Tisch, Mary R. Matthews

Materials Science

Calculations of the Krypton Phase Diagram and Novel Plasticity

Marcin Kirsz, Asuka Iwasaki and Graeme John Ackland

The phase diagram for Kr, as represented by the Tadah! two-body potential is shown to have face-centred cubic (fcc), hexahonal close packed (hcp), and body centred cubic (bcc) regions. It has been assembled by combining several methods: direct liquid–solid coexistence for the melt lines, Gibbs–Helmholtz integration and Clapeyron slopes for the bcc–fcc line, slab coexistence for the liquid–gas line, static zero-temperature relaxations for the crystals, and the quasiharmonic approximation for the low-temperature fcc–hcp windows. The bcc phase contains highly mobile “greedy snake" defects, which suggests a reinterpretation of the melt-curve data: the anomaly observed may be due to the speckle method detecting the bcc-fcc boundary, not the melt curve. While pair potentials have limitations, comparison with a foundation MACE model shows that a more flexible machine-learned model does not necessarily improve matters if inappropriately trained.
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Materials Science

ASE2SPRKKR: a unified Python framework integrating the Spin-Polarized Relativistic Korringa-Kohn-Rostoker method into the Atomic Simulation Environment

Ridha Eddhib, Matyáš Novák, Hubert Ebert et al. (+2 more)

The Spin-Polarized Relativistic Korringa-Kohn-Rostoker (SPR-KKR) is an all-electron ab-initio multiple-scattering code that provides unique capabilities for treating chemical disorder, finite-temperature magnetism, relativistic effects, and spectroscopic properties of various types of solids through its fundamental formulation in terms of the single-particle Green's function rather than eigenstates. We present ASE2SPRKKR, a comprehensive Python interface that integrates SPR-KKR into the Atomic Simulation Environment (ASE), making SPR-KKR more accessible, streamlined, and uniform. Our implementation extends the ASE's Atoms object to handle fractional site occupations for coherent-potential-approximation calculations while maintaining full compatibility with ASE's extensive ecosystem of structure builders, optimizers, and analysis tools. Automated input generation with validation, comprehensive output parsing, and direct MPI support enable seamless integration into high-throughput and multi-method workflows. We demonstrate the interface through representative applications: semi-infinite surface calculations reproducing Rashba-split Au(111) surface states; one-step photoemission modeling capturing matrix-element effects; exchange-parameter extraction for atomistic spin dynamics; and X-ray absorption spectroscopy including magnetic circular dichroism. Beyond these demonstrations, ASE2SPRKKR is designed with transferability as a first-class concern. By grounding its architecture in FAIR principles of Findability, Accessibility, Interoperability, and Reusability, it establishes a replicable blueprint for bringing other specialized Green's function and first-principles codes into the collaborative, reproducible workflows that modern materials discovery requires.
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All authors Ridha Eddhib, Matyáš Novák, Hubert Ebert, Aki Pulkkinen, Ján Minár

Materials Science

Jsymm: A Python package for symmetry analysis of exchange tensors in magnetic Hamiltonians

A.S. Sergeev and S.V. Streltsov

Symmetries of a crystal often restrict its physical properties. In particular, they determine possible forms of the tensors that describe interatomic exchange interaction, which governs a wide range of magnetic phenomena. Computationally demanding first-principles calculations of the exchange tensors can be greatly simplified by taking the symmetry constraints into account. Here, we present Jsymm, a Python package that derives the most general symmetry-compatible form of the exchange tensors directly from the crystallographic data. For any bond formed by magnetic ions, Jsymm produces the tensors of the Dzyaloshinskii-Moriya and anisotropic Heisenberg exchange interaction in symbolic form, as well as the tensors for all other bonds related to it by symmetry. This reduces the number of independent model parameters, dramatically lowering the computational cost of the ab initio calculations and preventing unphysical results arising from symmetry violations. The package accepts standard CIF files and provides a web interface in addition to an interactive text mode and a Python library. We demonstrate its utility on La$_2$CuO$_4$ and $\alpha$-Fe$_2$O$_3$, reproducing known symmetry constraints and revealing additional relations between components of the exchange tensors of different bonds.
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Materials Science

Tuning the Optoelectronics of Mixed-Semiconductors through the interplay of Quantum confinement and Stoichiometry Engineering

Kanha Ram Khator, Anupam Manna, Amlandeep Nayak et al. (+3 more)

All-inorganic cesium lead bromide (CsPbBr3) nanocrystals (NCs) have established themselves as an emerging semiconductor for next-generation optoelectronic technologies due to their unique combination of properties, such as near unity photoluminescence quantum yields, narrow color pure emission, and exceptional defect tolerance. Although size-dependent optical signatures of these NCs are well reported, the complexity of mixed ionic-electronic transport remains largely unexplored. In this study, we provide a comprehensive analysis of size-dependent charge transport by decoupling ionic and electronic transport dynamics through carefully designed transient current and space charge limited current measurements. By employing NCs of different sizes ranging from 5.6 nm to 11.3 nm in thin films, we provide a comprehensive understanding of quantum confinement effects and related synthetic chemistry. Contrary to popular beliefs of quantum confinement and band gap broadening, our results demonstrate that the smallest NCs exhibit the most efficient transport characteristics, evidenced by the lowest activation energy (hole activation energy = 78 meV) for hole transport and the highest barrier for vacancy-mediated ion migration (ion activation energy = 370 meV). This work paves a way forward for perovskite-based efficient quantum devices, by demonstrating that moving into a strong quantum confinement regime, a superior charge transport can be facilitated, when supported by carefully tailored stoichiometry.
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All authors Kanha Ram Khator, Anupam Manna, Amlandeep Nayak, Pravat Nayek, Prasenjit Mal, Satyaprasad P Senanayak

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

Correlated topological-polarization surface states in the narrow-gap insulator FeSb2

Takahiro Iwagaki, Hideki Matsuoka, Ginta Hoshino et al. (+7 more)

Strong electron correlations and band topology each generate rich quantum phases, but conflicting elemental requirements have largely kept them apart. Topological polarization offers a route to unite them, producing polar surface states from bonding charge without spin-orbit coupling and thereby extending band topology to correlated 3d transition-metal compounds. Here we demonstrate that epitaxial thin films of the narrow-gap insulator FeSb2 host metallic polar surface states of topological-polarization origin, governed by the strong correlations of the bulk. Nonreciprocal surface transport emerges only below the onset temperature of a correlation-driven reconstruction of the bulk Fe 3d orbital occupation, providing direct evidence of bulk-edge correspondence in a correlated topological system. Moreover, electrostatic gating drives this correlated surface across a quantum phase transition into a ferromagnetic or possibly altermagnetic state. Our results establish topological polarization as a design principle for correlated topological phases in a broad range of materials.
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All authors Takahiro Iwagaki, Hideki Matsuoka, Ginta Hoshino, Kanata Watanabe, Shungo Aoyagi, Shunsuke Kitou, Yuiga Nakamura, Motoaki Hirayama, Takashi Koretsune, Naoya Kanazawa