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Physics Condensed Matter Materials Science

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Tuesday 10 February

Materials Science

Chiralometer: Direct Torque Detection of Crystal Chirality

Nikolai Peshcherenko, Ning Mao, Claudia Felser et al. (+1 more)

Chirality governs phenomena ranging from chemical reactions to the topology of quasiparticle charge carriers. However, a direct macroscopic probe for crystal chirality remains a significant challenge, especially in time reversal symmetric systems with weak circular dichroism signal. Here, we propose the “Chiralometer”, a mechanical detection method that probes chirality by driving angular momentum carriers out of equilibrium. Using first-principles calculations and semiclassical transport theory, we demonstrate that a temperature gradient in insulators or an electric field in metals induces uncompensated angular momentum in phonons and electrons, respectively. This imbalance generates a macroscopic mechanical torque ($\tau \sim 10^{-11} N \cdot m$) well within the sensitivity of modern torque magnetometry and cantilever-based sensors. We identify robust signatures in chiral crystals such as Te, SiO$_2$, and the topological semimetal CoSi. Our work establishes mechanical torque as a fundamental order parameter for chirality, offering a transformative tool for orbitronics and chiral quantum materials.
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All authors Nikolai Peshcherenko, Ning Mao, Claudia Felser, Yang Zhang

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

Scattering theory of spin waves by lattice dislocation defects

Cristobal Larronde, Ignacio Castro, Alvaro S. Nunez et al. (+2 more)

We investigate spin-wave propagation in magnetic insulators in the presence of lattice dislocations. Within a continuum magnetoelastic framework, we show that the strain fields generated by dislocations induce equilibrium magnetic textures. The morphology of these textures depends sensitively on the dislocation type and acts as a localized scattering potential for spin-wave excitations. As a result, the scattering response exhibits pronounced asymmetries and interference effects governed by the magnetoelastic coupling and the dislocation type. By combining numerical simulations with analytical scattering theory, we compute differential cross sections and frequency-dependent transmission coefficients. Furthermore, analysis of the effective potential landscape reveals that the defect forms a barrier that modulates spin-wave transport and, crucially, breaks the intrinsic reflectionless nature of magnetic domain walls. Our findings identify lattice dislocations as tunable scattering centers, opening new avenues for defect engineering in magnonic devices.
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All authors Cristobal Larronde, Ignacio Castro, Alvaro S. Nunez, Roberto E. Troncoso, Nicolas Vidal-Silva

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

Origin of Moiré Potentials in WS$_2$/WSe$_2$ Heterobilayers: Contributions from Lattice Reconstruction and Interlayer Charge Transfer

Youwen Wang, Nanya Gao and Qingjun Tong

Moiré superlattices formed in WS$_2$/WSe$_2$ heterobilayers have emerged as an exciting platform to explore the quantum many-body physics. The key mechanism is the introduction of moiré potentials for the band-edge carriers induced by the lateral modulation of interlayer interactions. This trapping potential results in the formation of flat bands, which enhances the strong correlation effect. However, a full understanding of the origin of this intriguing potential remains elusive. In this paper, we present a comprehensive investigation of the origin of moiré potentials in both R-type and H-type moiré patterns formed in WS$_2$/WSe$_2$ heterobilayers. We show that both lattice reconstruction and interlayer charge transfer contribute significantly to the formation of moiré potentials. In particular, the lattice reconstruction induces a nonuniform local strain, which creates an energy modulation of 200 meV for the conduction band-edge state located at WS$_2$ layer and 20 meV for the valence band-edge state located at WSe$_2$ layer. In addition, the lattice reconstruction also introduces a piezopotential energy, whose amplitude ranges from 40 meV to 90 meV depending on the stacking and band-edge carrier. The interlayer charge transfer induces a built-in electric field, resulting in an energy modulation of 80 meV for an R-type moiré and 40 meV for an H-type moiré. Taking into account both effects from lattice reconstruction and interlayer charge transfer, the formation of moiré potential is well understood for both R-type and H-type moirés. This trapping potential localizes the wavefunctions of conduction and valence bands around the same moiré site for an R-type moiré, while around different moiré site for an H-type one.
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Materials Science

Competing magnetic states in a non-coplanar Kagome magnet

Xiaodong Hu, Amar Fakhredine, Roger Guzman et al. (+15 more)

Non-collinear Kagome antiferromagnets (AFMs) Mn3X (X = Sn, Ga, Ge, Ir, Pt) can generate an anomalous Hall effect (AHE) despite vanishing net magnetization, enabled by broken time-reversal and inversion symmetries. However, strong in-plane anisotropy has limited studies of the AFM-AHE and electronic applications to coplanar spin configurations. Non-coplanar spin textures in these systems have been realized only in low temperature spin-glass states or at interfaces with heavy metals. Here, we report an intrinsic non-coplanar spin configuration persisting up to 400 K in cubic-phase Mn3Ge, originating from coexisting symmetric and antisymmetric exchange interactions. Competing magnetic states associated with this non-coplanar spin configuration give rise to an unconventional AHE with a magnetic-field-induced sign reversal and a hump-like feature. Our findings establish a platform for non-coplanar magnetism in AFM spintronics.
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All authors Xiaodong Hu, Amar Fakhredine, Roger Guzman, Martin Frentrup, Jinan Shi, Giulio I. Lampronti, Sami El-Khatib, Waichuen Tse, Laura Gorzawski, Angelo Di Bernardo, Nadia Stelmashenko, Wu Zhou, Mehmet Egilmez, Danfeng Li, Grzegorz P. Mazur, Mario Cuoco, Carmine Autieri, Jason W. A. Robinson

Materials Science

Realistic tight-binding model for V2Se2O-family altermagnets

Xingkai Cheng, Yifan Gao and Junjie Pengand Junwei Liu

Following earlier theoretical prediction, intercalated V2Se2O-family altermagnets such as RbV2Te2O and KV2Se2O have now been experimentally confirmed as d-wave altermagnets, representing the only known van der Waals layered altermagnetic systems. By combining crystal-symmetry-paired spin-momentum locking (CSML) with the layered structure, the V2Se2O-family offers a suitable platform for studying low-dimensional spintronic responses and exploring the interplay among multiple quantum degrees of freedom. To establish a concrete theoretical foundation for understanding and utilizing these materials, we investigate six representative members of the V2Se2O-family and construct a realistic tight-binding model parameterized by first-principles calculations, which is benchmarked by experimental measurements. This model accurately captures essential altermagnetic electronic properties, including CSML and noncollinear spin-conserved currents. It further incorporates strain-coupling parameters, enabling the simulation of strain-tunable responses such as the piezo-Hall effects. This realistic model allows systematic exploration of multiple degrees of freedom (like spin, valley, and layer) within a single system, and lays the groundwork for understanding their coupling with other quantum materials, such as topological insulators and superconductors, thereby advancing both the fundamental understanding and potential device applications of this novel class of layered altermagnets.
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Materials Science

Nodal-Surface and Flat-Band Driven Large Anomalous Nernst Effect in Epitaxial Ferromagnetic Weyl Metal Fe5Si3

Shubhashish Pati, Sonali Srotaswini Pradhan, Nanhe Kumar Gupta et al. (+7 more)

Magnetic topological materials such as Weyl and Dirac magnets exhibit unconventional electronic properties arising from the interplay between magnetic order and band topology, leading to remarkable thermomagnetic and thermoelectric effects. Here, we investigate the ANE in epitaxial thin films of the Weyl ferromagnet candidate Fe5Si3. A pronounced transverse Nernst response exceeding approximately 1.50 microvolt per kelvin is observed at room temperature, together with a giant anomalous Nernst angle of about 0.56, indicating highly efficient conversion between thermal gradients and transverse electric fields. Beyond the anomalous contribution, a sizable topological Nernst signal of approximately 0.43 microvolt per kelvin persists above room temperature, suggesting the possible presence of real-space Berry curvature associated with nontrivial spin textures. First-principles density functional theory calculations combined with symmetry analysis reveal an unconventional electronic structure in which Weyl nodal lines, nodal surfaces, and nearly flat bands coexist near the Fermi level. This rare concurrence of multiple topological band features produces a strongly enhanced and sharply energy-dependent Berry curvature, which governs both the magnitude and temperature evolution of the observed Nernst response. The close quantitative agreement between calculated anomalous Nernst conductivity and experimental results establishes the topological electronic structure as the dominant origin of the observed thermomagnetic transport, highlighting Fe5Si3 as a chemically simple, low-cost binary topological magnet for exploring both real-space and momentum-space Berry-curvature-driven thermoelectric phenomena.
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All authors Shubhashish Pati, Sonali Srotaswini Pradhan, Nanhe Kumar Gupta, Abhay Pandey, Nikita Sharma, Nakul Kumar, Saurav Singh, Yuya Sakuraba, V. Kanchana, Sujeet Chaudhary

Materials Science · Cross-listed from physics.optics

Non-Hermitian stealthy hyperuniformity

Gitae Lee, Seungmok Youn, Ikbeom Lee et al. (+5 more)

Symmetry-driven wave physics in open systems, exemplified by parity-time (PT) symmetry, has extended the landscape of crystalline phases in materials science to include gain-loss media. Given the growing interest in engineering disorder for wave manipulation, such non-Hermitian crystals motivate the extension of non-Hermitian frameworks into the realm of correlated disorder. Here, we propose hyperuniformity and stealthiness in non-Hermitian systems as a generalization of PT-symmetric crystals to correlated disorder. We extend the scattering-microstructure correspondence to open systems, formulating non-Hermitian hyperuniformity and stealthiness that encompass their Hermitian counterparts. This approach, incorporating a statistical crystallography framework for non-Hermitian materials, demonstrates that real-imaginary cross-correlations of the material potential are irrelevant for achieving hyperuniformity but are essential for characterizing stealthiness, revealing unidirectional scattering phases that are inaccessible in Hermitian materials and in non-Hermitian crystals. By analysing the microstructural statistics of the resulting materials, our results, building on non-Hermitian wave physics, establish a connection to materials science, encompassing conventional descriptors of correlated disorder.
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All authors Gitae Lee, Seungmok Youn, Ikbeom Lee, Kunwoo Park, Duhwan Hwang, Xianji Piao, Namkyoo Park, Sunkyu Yu

Materials Science

Surface-State-Driven Anomalous Hall Effect in Altermagnetic MnTe Films

Ling-Jie Zhou, Zi-Jie Yan, Hongtao Rong et al. (+15 more)

Altermagnets have recently emerged as a new class of magnetic materials that combine compensated magnetic order with spin-split electronic band structures. In this work, we employ molecular beam epitaxy to grow MnTe thin films with controlled thickness on InP(111)A substrates. By performing angle-resolved photoemission spectroscopy measurements, we observe a large spin splitting of ~230 meV for bulk bands well below the Fermi level and identify surface states that cross the Fermi level. Electrical transport measurements reveal that a robust anomalous Hall (AH) effect persists down to 2 K and an AH sign reversal occurs near 175 K. By systematically tuning film thickness, growth conditions, and interfacial structure, we demonstrate that the AH response in MnTe films originates from the Berry curvature of surface states rather than from bulk bands. Our first-principles calculations reveal that this surface-state-driven AH effect is imprinted by the bulk altermagnetic order and remains unchanged for terminations with opposite Mn magnetic orientations. Our results establish a unique surface transport probe of bulk altermagnetism, demonstrate interface engineering as an effective route to generate and control the AH effect in altermagnets, and provide a unified understanding of the AH response in altermagentic MnTe films.
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All authors Ling-Jie Zhou, Zi-Jie Yan, Hongtao Rong, Yufei Zhao, Pu Xiao, Lok-Kan Lai, Zhiyuan Xi, Ke Wang, Tibendra Adhikari, Ganesh P. Tiwari, Zhong Lin, Pascal Manue, Fabio Orlandi, Dmitry Khalyavin, Alexander J. Grutter, Chao-Xing Liu, Binghai Yan, Cui-Zu Chang

Materials Science

Interplay of Quantum Size Effect and Tensile Strain on Surface Morphology of Sn(100) Islands

Bing Xia, Xiaoyin Li, Hongyuan Chen et al. (+16 more)

The quantum size effect (QSE) and strain effect are two key factors influencing the surface morphology of thin films, which can increase film surface roughness through QSE-induced thickness oscillation and strain-induced island formation, respectively. Surface roughness usually manifests in the early stages of film growth and diminishes beyond a critical thickness. In this work, we employ molecular beam epitaxy (MBE) to grow Sn(100) islands with varying thickness N on bilayer graphene-terminated 6H-SiC(0001) substrates. Scanning tunneling microscopy and spectroscopy measurements reveal an inverse surface roughness effect that highlights the interplay of QSE and misfit strain in shaping the surface morphology of Sn(100) islands. For N =< 10, the islands exhibit flat surfaces, while for N >= 26, the island surfaces become corrugated and patterned. For the intermediate range, i.e., 12 =< N =<24, both flat and patterned surfaces coexist, with the percentage coverage of the patterned surface oscillating as a function of N. By performing density functional theory calculations, we demonstrate that the unusual surface pattern evolution in our MBE-grown Sn(100) islands is a result of the interplay between QSE-induced surface roughing and tensile strain-induced smoothening effect.
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All authors Bing Xia, Xiaoyin Li, Hongyuan Chen, Bo Yang, Jie Cai, Stephen Paolini, Zihao Wang, Zi-Jie Yan, Hao Yang, Xiaoxue Liu, Liang Liu, Dandan Guan, Shiyong Wang, Yaoyi Li, Canhua Liu, Hao Zheng, Cui-Zu Chang, Feng Liu, Jinfeng Jia

Materials Science

How Far Can You Grow? Characterizing the Extrapolation Frontier of Graph Generative Models for Materials Science

Can Polat, Erchin Serpedin, Mustafa Kurban et al. (+1 more)

Every generative model for crystalline materials harbors a critical structure size beyond which its outputs become unreliable; we call this the extrapolation frontier. Despite its consequences for nanomaterial design, this frontier has never been systematically measured. We introduce RADII, a radius-resolved benchmark of ~75,000 crystal-derived nanoparticle structures (33-11,298 atoms) that treats radius as a continuous scaling knob, tracing generation quality from in- to out-of-distribution under leakage-free splits. Each model is conditioned on target composition and atom count, isolating geometric extrapolation as the evaluation variable. RADII provides frontier-specific diagnostics: per-radius error profiles pinpoint each architecture's scaling ceiling, surface-interior decomposition separates boundary from bulk failures, and cross-metric sequencing reveals which aspect of structural fidelity breaks first. Benchmarking five state-of-the-art architectures, we find that: (i) well-behaved models degrade by ~13% in global positional error beyond training radii, while divergent models show poor fidelity across scales, with local bond fidelity ranging from negligible degradation to over 2x error growth; (ii) no two architectures share a failure sequence, revealing the frontier as a multi-dimensional surface shaped by model family; and (iii) well-behaved models follow the expected geometric scaling exponent alpha ~ 1/3, whose in-distribution fit predicts out-of-distribution error, making frontiers forecastable. Scaling MatterGen to its published parameter count stabilizes sampling but does not close the frontier, while DiffCSP remains unstable at published scale. These findings establish output scale as a first-class evaluation axis for geometric generative models. Code and data: https://github.com/KurbanIntelligenceLab/RADII.
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All authors Can Polat, Erchin Serpedin, Mustafa Kurban, Hasan Kurban

Monday 9 February

Materials Science

Deformation-Potential-Driven Photostriction in Layered Ferroelectrics

S. Puri, R. Rodriguez, C. Dansou et al. (+5 more)

The coupling between electronic excitations and lattice deformation in van der Waals ferroelectrics is governed by a competition between the electron deformation potential and the inverse piezoelectric effect. While theory predicts that piezoelectric screening should drive a polar-axis contraction in monolayer group-IV monochalcogenides, we demonstrate that in multilayer SnS, the deformation potential provides the dominant contribution, driving a polar-axis expansion even within ferroelectric domains. By correlating polarization-resolved second-harmonic generation microscopy with ultrafast reflectance spectroscopy and first-principles calculations, we resolve the anisotropic lattice response and disentangle intrinsic photostrictive strain from extrinsic thin-film interference artifacts. These results establish a microscopic hierarchy of photostrictive mechanisms and position stacking-engineered SnS as a platform for ultrafast optomechanical transduction.
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All authors S. Puri, R. Rodriguez, C. Dansou, L. Bouric, A. Sheibani, C. Paillard, L. Bellaiche, H. Nakamura

Materials Science

Stress-Induced Ferroelectricity in Hafnium Oxide Core-Shell Nanoparticles

Anna N. Morozovska, Eugene A. Eliseev, Richard Liu et al. (+2 more)

In contrast to hafnia (HfO2) thin films, where the appearance of switchable ferroelectric polarization can be induced by strain or defect engineering, reliable methods for controlling ferroelectricity are absent in HfO2 nanoparticles. Direct experimental observations of ferroelectric hysteresis and ferroelectric domains in these nanoparticles are also absent. To the best of our knowledge, stress-induced ferroelectric states in the HfO2 nanoparticles have not been explored. In this work, we study the influence of chemical stress on phase diagrams, dielectric and polar properties of spherical HfO2 core-shell nanoparticles using a Landau-Ginzburg-Devonshire free energy functional that includes trilinear and biquadratic couplings involving polar, antipolar, and nonpolar order parameters. The ferroelectric phase exhibits reentrant behavior as a function of nanoparticle size, such that the spontaneous polarization exists only within a limited range of core radii R_c, namely R_cr^min<R_c<R_cr^max. The minimal critical radius R_cr^min is primarily determined by the size dependence of the depolarization field and correlation effects; the maximal critical radius R_cr^max is primarily determined by the size dependence of chemical stresses induced by the elastic defects in the shell. Thus, this work identifies a stress-driven mechanism for reentrant ferroelectricity stabilization in nanoscale HfO2 systems, arising from the competition between depolarization field-induced suppression of ferroelectricity and its stabilization by shell-induced chemical stress. We revealed that relatively large compressive chemical strains are necessary to induce the ferroelectric phase in the HfO2 nanoparticles. Successful chemical strain engineering opens the way for significant enhancement of nanoscale HfO2 polar properties for applications in advanced memory cells and logic devices.
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All authors Anna N. Morozovska, Eugene A. Eliseev, Richard Liu, Sergei V. Kalinin, Dean R. Evans

Materials Science

Adsorption of Water on Pristine Graphene: A van der Waals Density Functional Study with the vdW-C09 Approach

Aline Oliveira Santos, Bruno H. S. Mendonça and Elizane E. de Moraes

Understanding how water interacts with graphene at the molecular level is essential for advancing nanomaterial applications in filtration, catalysis, and environmental technologies. This study establishes a quantitative baseline for assessing how structural defects, dopants, or surface functionalization may enhance water adsorption, providing insights for the rational design of graphene-based materials in water purification, sensing, and nanofluidic applications. In this work, we employed density functional theory (DFT) with the vdW-C09 functional to investigate the adsorption of a single water molecule on pristine graphene, accurately accounting for long-range dispersion forces. Three high-symmetry adsorption sites-the center of the hexagonal ring, the C-C bond, and the top site-were explored in combination with three molecular orientations: Down, H-bond, and Up configurations. The calculated adsorption energies range from -93 to -145 meV (milli-electron volts), indicating that the interaction is dominated by weak van der Waals forces characteristic of physisorption. The most stable configuration corresponds to the Down orientation above the center of the hexagonal ring, with an adsorption energy of -145 meV and an equilibrium distance of 3.27 A (angstrom), defined as the vertical separation between the oxygen atom of the water molecule and the graphene plane. These results are in close agreement with previous theoretical studies and confirm the non-reactive and hydrophobic nature of pristine graphene.
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Materials Science

Chiral Polar Eu2(SeO3)2(SO4)(H2O)2: A Pathway Toward Narrow Optical Linewidths and Microsecond Lifetimes for Quantum Memory Candidates

Uchenna Chinaegbomkpa, Ebube Oyeka, Xudong Huai et al. (+5 more)

Stoichiometric materials of Eu(III) offer a promising platform for quantum memories attributable to their unique capability to display a distinctive, nondegenerate J = 0 transition, which enables precise mapping of optical quantum states into their hyperfine structure for reliable storage and retrieval on demand. However, placing Eu(III) into chiral polar structures, which are necessary for achieving narrow spectral linewidths and long optical lifetimes, is a daunting task. Here, we discover Eu2(SeO3)2(SO4)(H2O)2, a rare Eu(III) material that exhibits chiral polar symmetries encompassing both local and global structures. This unique structure is shaped by an appropriate combination of asymmetric ligands. The chirality fosters dipole-dipole interactions and J-mixing, as characterized by second-harmonic generation, photoluminescence, and magnetic susceptibility. The broken inversion symmetry is supported by the phase-matching behavior of second-harmonic generation. The J = 0 transition is observed at 578 nm with a narrow linewidth at 78 K and a microsecond-scale optical lifetime. The analysis of magnetic susceptibility data using Van Vleck theory results in an effective magnetic moment of 3.33 {\mu}B/Eu3+ and J-mixing. Heat capacity data reveal underlying phonon dynamics in the material. This study demonstrates a pathway toward realizing new stoichiometric Eu3+ compounds with potential for optically addressable quantum memory applications.
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All authors Uchenna Chinaegbomkpa, Ebube Oyeka, Xudong Huai, Ramesh Kumar, Mingli Liang, Jakoah Brgoch, Hugo Sanabria, Thao T. Tran

Materials Science · Cross-listed from cs.LG

Boltzmann Reinforcement Learning for Noise resilience in Analog Ising Machines

Aditya Choudhary, Saaketh Desai and Prasad Iyer

Analog Ising machines (AIMs) have emerged as a promising paradigm for combinatorial optimization, utilizing physical dynamics to solve Ising problems with high energy efficiency. However, the performance of traditional optimization and sampling algorithms on these platforms is often limited by inherent measurement noise. We introduce BRAIN (Boltzmann Reinforcement for Analog Ising Networks), a distribution learning framework that utilizes variational reinforcement learning to approximate the Boltzmann distribution. By shifting from state-by-state sampling to aggregating information across multiple noisy measurements, BRAIN is resilient to Gaussian noise characteristic of AIMs. We evaluate BRAIN across diverse combinatorial topologies, including the Curie-Weiss and 2D nearest-neighbor Ising systems. We find that under realistic 3% Gaussian measurement noise, BRAIN maintains 98% ground state fidelity, whereas Markov Chain Monte Carlo (MCMC) methods degrade to 51% fidelity. Furthermore, BRAIN reaches the MCMC-equivalent solution up to 192x faster under these conditions. BRAIN exhibits $\mathcal{O}(N^{1.55})$ scaling up to 65,536 spins and maintains robustness against severe measurement uncertainty up to 40%. Beyond ground state optimization, BRAIN accurately captures thermodynamic phase transitions and metastable states, providing a scalable and noise-resilient method for utilizing analog computing architectures in complex optimizations.
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Materials Science

Fixed-grid sharp-interface numerical solutions to the three-phase spherical Stefan problem

Yavkreet Swami, Jacob Barajas and Amneet Pal Singh Bhalla

Many metal manufacturing processes involve phase change phenomena, which include melting, boiling, and vaporization. These phenomena often occur concurrently. A prototypical 1D model for understanding the phase change phenomena is the Stefan problem. There is a large body of literature discussing the analytical solution to the two-phase Stefan problem that describes only the melting or boiling of phase change materials (PCMs) with one moving interface. Density-change effects that induce additional fluid flow during phase change are generally neglected in the literature to simplify the math of the Stefan problem. In our recent work [1], we provide analytical and numerical solutions to the three-phase Stefan problem with simultaneous occurrences of melting, solidification, boiling, and condensation in Cartesian coordinates. Our current work builds on our previous work to solve a more challenging problem: the three-phase Stefan problem in spherical coordinates for finite-sized particles. There are three moving interfaces in this system: the melt front, the boiling front, and the outer boundary which is in contact with the atmosphere. Although an analytical solution could not be found for this problem, we solved the governing equations using a fixed-grid sharp-interface method with second-order spatio-temporal accuracy. Using a small-time analytical solution, we predict a reasonably accurate estimate of temperature (in the three phases) and interface positions and velocities at the start of the simulation. Our numerical method is validated by reproducing the two-phase nanoparticle melting results of Font et al. [2]. Lastly, we solve the three-phase Stefan problems numerically to demonstrate the importance of kinetic energy terms during phase change of smaller (nano) particles. In contrast, these effects diminish for large particles (microns and larger).
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Materials Science

Tailoring Ultrathin Magnetic Multilayers at Terraced Topologically Insulating Interfaces for Perpendicularly Magnetized Domains

Benjamin A. Brereton, Soumyarup Hait, Ahmet Yagmur et al. (+8 more)

Topological insulators and skyrmion-hosting, chiral magnetic multilayers are two well-explored areas of modern condensed matter physics, each offering unique advantages for spintronics applications. In this paper, we demonstrate the optimization process for the growth of a Bi$_2$Se$_3$/buffer/[Pt/CoB/Ru]$_{\times N}$ heterostructure that combines these two material classes: the Bi$_2$Se$_3$ epilayer was grown by molecular beam epitaxy before transfer under ultrahigh vacuum to a separate growth chamber where the polycrystalline metallic multilayer was sputter deposited. The structure of the samples was characterized by co-fitted X-ray and polarized neutron reflectometry measurements and scanning transmission electron microscopy. Polarized neutron models and standard magnetometry show that a buffer layer exceeding a critical thickness is required to obtain the desired uniform, perpendicular magnetic anisotropy in every magnetic layer in the multilayer. Samples with both Ta and Mo buffers were used requiring thicknesses of 1.5 and 0.9 nm respectively. In minimizing the Bi$_2$Se$_3$ terracing, buffered samples yield well-defined, out-of-plane, magnetic domains suitable for spin-orbit torque induced manipulation as determined by X-ray photoemission electron microscopy.
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All authors Benjamin A. Brereton, Soumyarup Hait, Ahmet Yagmur, Christy J. Kinane, Francesco Maccherozzi, Michele Conroy, Satoshi Sasaki, Thomas A. Moore, Sarnjeet S. Dhesi, Sean Langridge, Christopher H. Marrows

Materials Science

The role of absorption in three-dimensional electron diffraction dynamical structure refinement

Benjamin Colmey, Tiarnan A.S. Doherty, Shreshth A. Malik et al. (+1 more)

The role of absorption in 3D electron diffraction is established through analytical theory, simulation, and dynamical refinement. A two-beam expression for the absorbed integrated intensity in centrosymmetric crystals is derived, showing that for $t/\xi_g \ll 1$ reflections follow a uniform exponential decay set by the mean absorptive potential $U_0'$. Many-beam simulations of both centrosymmetric and non-centrosymmetric crystals reveal additional reflection-specific anomalous absorption beyond the uniform attenuation set by $U_0'$. Neglecting these effects in dynamical refinement of integrated intensities incurs an error that increases approximately linearly with thickness, with this error becoming more severe near zone axes. Dynamical refinements were performed on CsPbBr$_3$, quartz, and borane, with the inclusion of absorption yielding an improvement in $R_{\mathrm{obs}}$ from $6.4$ to $5.3$ % for CsPbBr$_3$ and negligible improvements for quartz and borane. Anomalous absorption may therefore be ignored for routine refinement of integrated intensities except in high-$Z$ materials at thicknesses approaching $\xi_g $.
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All authors Benjamin Colmey, Tiarnan A.S. Doherty, Shreshth A. Malik, Paul A. Midgley

Materials Science · Cross-listed from quant-ph

Spin-active chlorine-related centers in 4H-SiC with telecom-band emissions

Danial Shafizadeh, Misagh Ghezellou, Viktor M. Bobal et al. (+5 more)

A photoluminescence (PL) and magnetic resonance investigation of a defect in chlorine-implanted 4H-SiC is presented. This Cl-related center emits light at telecom wavelengths with zero-phonon lines in the range 1350-1540 nm. Its four configurations exhibit stable PL spectra characterized by narrow zero-phonon lines. For the two configurations that emit light at the C-band, a Debye-Waller factor in the range 22-25% is estimated. Optically detected magnetic resonance confirms that the Cl-related center is spin active and stable at room temperature with the zero-field splitting in the range of 1.0-1.4 GHz. The combined optical and spin properties suggest this center to be a highly promising candidate for scalable quantum networks.
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All authors Danial Shafizadeh, Misagh Ghezellou, Viktor M. Bobal, Lasse Vines, Jawad Ul-Hassan, Valdas Jokubavicius, Nguyen T. Son, Ivan G. Ivanov

Materials Science · Cross-listed from stat.ML

Cutting Through the Noise: On-the-fly Outlier Detection for Robust Training of Machine Learning Interatomic Potentials

Terry C. W. Lam, Niamh O'Neill, Christoph Schran et al. (+1 more)

The accuracy of machine learning interatomic potentials suffers from reference data that contains numerical noise. Often originating from unconverged or inconsistent electronic-structure calculations, this noise is challenging to identify. Existing mitigation strategies such as manual filtering or iterative refinement of outliers, require either substantial expert effort or multiple expensive retraining cycles, making them difficult to scale to large datasets. Here, we introduce an on-the-fly outlier detection scheme that automatically down-weights noisy samples, without requiring additional reference calculations. By tracking the loss distribution via an exponential moving average, this unsupervised method identifies outliers throughout a single training run. We show that this approach prevents overfitting and matches the performance of iterative refinement baselines with significantly reduced overhead. The method's effectiveness is demonstrated by recovering accurate physical observables for liquid water from unconverged reference data, including diffusion coefficients. Furthermore, we validate its scalability by training a foundation model for organic chemistry on the SPICE dataset, where it reduces energy errors by a factor of three. This framework provides a simple, automated solution for training robust models on imperfect datasets across dataset sizes.
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All authors Terry C. W. Lam, Niamh O'Neill, Christoph Schran, Lars L. Schaaf

Materials Science

Flash annealing-engineered wafer-scale relaxor antiferroelectrics for enhanced energy storage performance

Yizhuo Li, Kepeng Song, Meixiong Zhu et al. (+11 more)

Dielectric capacitors are essential for energy storage systems due to their high-power density and fast operation speed. However, optimizing energy storage density with concurrent thermal stability remains a substantial challenge. Here, we develop a flash annealing process with ultrafast heating and cooling rates of 1000 oC/s, which facilitates the rapid crystallization of PbZrO3 film within a mere second, while locking its high-temperature microstructure to room temperature. This produces compact films with sub-grain boundaries fraction of 36%, nanodomains of several nanometers, and negligible lead volatilization. These contribute to relaxor antiferroelectric film with a high breakdown strength (4800 kV/cm) and large polarization (70 uC/cm2). Consequently, we have achieved a high energy storage density of 63.5 J/cm3 and outstanding thermal stability with performance degradation less than 3% up to 250 oC. Our approach is extendable to ferroelectrics like Pb(Zr0.52Ti0.48)O3 and on wafer scale, providing on-chip nonlinear dielectric energy storage solutions with industrial scalability.
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All authors Yizhuo Li, Kepeng Song, Meixiong Zhu, Xiaoqi Li, Zhaowei Zeng, KangMing Luo, Yuxuan Jiang, Zhe Zhang, Cuihong Li, Yujia Wang, Bing Li, Zhihong Wang, Zhidong Zhang, Weijin Hu

Materials Science

$d$-wave Surface Altermagnetism in Centrosymmetric Collinear Antiferromagnets

Ersoy Sasioglu, Ingrid Mertig and Samir Lounis

Broken inversion symmetry at the surfaces of centrosymmetric collinear antiferromagnets lifts combined inversion and time-reversal symmetry ($PT$) and can, in principle, enable nonrelativistic d-wave spin splitting, termed surface altermagnetism. Combining symmetry analysis with first-principles calculations, we show that surface inversion breaking, while necessary, is not sufficient for this effect. Surface altermagnetism emerges only when no antiunitary symmetry survives at the surface that exchanges the two antiferromagnetically coupled surface sublattices and enforces spin degeneracy. We demonstrate this mechanism explicitly for the centrosymmetric G-type antiferromagnets V$_3$Al and BaMn$_2$Sb$_2$, and contrast it with MnPt, where a sublattice-exchanging symmetry survives at the surface in the form of translation-time-reversal symmetry ($tT$), thereby preserving spin degeneracy despite broken inversion symmetry. The mechanism is shown to apply across multiple classes of centrosymmetric antiferromagnets and remains robust against spin-orbit coupling, although relativistic spin mixing in heavier-element compounds may reduce the observable spin polarization. These results establish a symmetry-based route toward realizing robust nonrelativistic momentum-dependent spin polarization at antiferromagnetic surfaces and interfaces.
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Materials Science

Emergent altermagnetism at surfaces of antiferromagnets: full symmetry classification and material identification

Colin Lange, Rodrigo Jaeschke-Ubiergo, Atasi Chakraborty et al. (+4 more)

We demonstrate the emergence of altermagnetism at the surfaces of antiferromagnets, vastly expanding the number of material candidates with altermagnetic characteristics and establishing a route towards two-dimensional altermagnetism through surface-induced symmetry breaking. We do so by developing a surface spin group formalism that fully classifies all surface magnetic states and identifies altermagnetic surface spin groups that can arise at the surfaces of antiferromagnets. We use this formalism to identify over 150 antiferromagnetic entries from the MAGNDATA database with at least one altermagnetic surface, often times with multiple such surfaces in the same material, and clarify the role of surface roughness and terraces. We illustrate this emergent phenomenon in a realistic Lieb lattice-based minimal model and present ab initio calculations on two representative material candidates, $\text{NaMnP}$ and $\text{FeGe}_2$, exhibiting $d$-wave and $g$-wave surface altermagnetism, respectively. Our theory naturally resolves the contradiction of recent experimental reports of $d$-wave spin splitting from ARPES measurements on metallic Lieb lattice compounds such as KV$_2$Se$_2$O that have been shown to be antiferromagnetic in the bulk. Hence, we establish a new paradigm for generating effectively two-dimensional altermagnetism by functionalizing the abundant material class of collinear antiferromagnets as viable platforms for controlled surface altermagnetism.
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All authors Colin Lange, Rodrigo Jaeschke-Ubiergo, Atasi Chakraborty, Xanthe H. Verbeek, Libor Šmejkal, Jairo Sinova, Alexander Mook

Materials Science · Cross-listed from quant-ph

Heterogeneous Optically-Detected Spin-Acoustic Resonance in Solid-State Molecular Thin-film

Kuan-Cheng Chen, Yongqiang Wen, Xiaotian Xu et al. (+7 more)

We report an implementation of spin-acoustic resonance in pentacene thin films integrated on a high-quality-factor (high-Q) surface acoustic wave (SAW) resonator on a lithium niobate substrate. Heterogeneous optically detected spin-acoustic resonance (HODSAR) is an optically detected spin-resonance measurement in which the resonant drive is delivered mechanically by a surface acoustic wave (SAW). By leveraging the photo-excited triplet state of pentacene at room temperature, we demonstrate coherent spin manipulation via acoustic driving under zero externally applied magnetic field. The heterogeneously integrated device, referred to as HODSAR, utilizes spin-phonon coupling to achieve mechanically driven, zero-field spin resonance, opening avenues for room-temperature mechanically addressable spin control and device integration. We show that the high-Q multimode response of the SAW resonator enables spectrally selective acoustic addressing of triplet transitions near 105 MHz. Coherent control is evidenced by Rabi oscillations, with a Rabi frequency that increases linearly with the square root of the applied RF input power over the measured drive range, consistent with driven two-level dynamics under acoustic excitation. These results establish spin-acoustic resonance in a heterogeneously integrated molecular thin-film platform and provide a quantitative basis for benchmarking mechanically mediated spin control.
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All authors Kuan-Cheng Chen, Yongqiang Wen, Xiaotian Xu, Max Attwood, Jingdong Xu, Chen Fu, Sami Ramadan, Shang Yu, Sandrine Heutz, Mark Oxborrow

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

Topological properties of spin block magnetic ladders in proximity of a superconductor: application to BaFe$_{2}$S$_{3}$

Shivam Yadav, Pascal Simon and Andrzej Ptok

Monoatomic chains with magnetic order in proximity of a s-wave superconductor can host Majorana edge modes. In this paper, we extend this idea to more complex spin-block chains such as the BaFe$_{2}$S$_{3}$ magnetic material that has a spin-ladder like structure. We investigate the topological phase diagram of such a system as function of the system parameters. We show that the coupling between chains within the ladder leads to the topological phase with a winding number larger than the sum of two single magnetic chains. Furthermore, strong coupling between chains leads to fractal-like substructure in the topological phase diagram. By investigating the real space properties of such a system and particularly its edge modes, we find that the system spectrum contains several in-gap states that we analyze in detail.
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Materials Science · Cross-listed from physics.app-ph

Germanium Thermophotovoltaic Devices Achieving 7.3% Efficiency Under High-Temperature Emission by Empirical Calorimetry

A. M. Medrano, E. Lopez, Pablo Garcia-Linares et al. (+6 more)

We report the first empirical efficiency measurement of germanium-based thermophotovoltaic devices under high-temperature, high-irradiance conditions using a high view-factor calorimetric setup. Two TPV cell architectures were fabricated on p-type, highly doped (10^17 cm-3) Ge substrates, differing only in rear contact configuration. A standard device with a gold rear contact achieves a peak efficiency of 7.3 % and a power density of 1.77 W/cm2 at an emitter temperature of 1480 C, while a PERC-type device reaches 6.3 % efficiency and 1.22 W/cm2 at 1426 C. The superior performance of the standard device is attributed to lower series resistance, whereas the PERC design exhibits slightly higher efficiency at lower emitter temperatures (4.0 % vs. 3.8 % at 1150 C) due to enhanced rear-surface reflectivity. A detailed TPV model has been developed and validated across both device architectures. The model identifies out-of-band optical losses as the dominant efficiency-limiting mechanism, primarily caused by strong free-carrier absorption in the highly doped Ge substrate. Using this model, we predict device performance under idealized spectral conditions commonly assumed in prior literature. For a simulated AlN/W spectrally selective emitter, efficiencies as high as 22.3 % at 1800 C are obtained, consistent with previous semi-empirical predictions. In contrast, when previously reported Ge devices are modeled under the realistic graphite emitter spectrum used here, projected efficiencies decrease to as low as 8.1 % at 1480 C. These results show that earlier projections remain valid but idealized and underscore the importance of emitter spectral engineering and substrate optimization. Finally, we present the first direct comparison of Ge and InGaAs TPV devices under identical conditions, demonstrating the superior performance of InGaAs while confirming the cost-driven competitiveness of Ge.
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All authors A. M. Medrano, E. Lopez, Pablo Garcia-Linares, J. Villa, M. Gamel, M. Garin, I. Martin, C. Canizo, A. Datas

Materials Science

NMRPeak: a ready-to-use intelligent system for molecular structure elucidation enabled by synergistic cross-modal learning

Fanjie Xu, Jinyuan Hu, Jingxiang Zou et al. (+8 more)

One-dimensional nuclear magnetic resonance (NMR) spectroscopy is essential for molecular structure elucidation in organic synthesis, drug discovery, natural product characterization, and metabolomics, yet its interpretation remains heavily dependent on expert knowledge and difficult to scale. Although machine learning has been applied to NMR spectrum prediction, library retrieval, and structure generation, these tasks have evolved in isolation using simulated data and incompatible spectral representations, limiting their utility under real experimental scenarios. Here we present NMRPeak, a unified cross-modal learning system that integrates these three tasks through experimentally grounded design. We curate approximately 1.8 million experimental and simulated spectra to construct the largest benchmark for NMR-based structure elucidation and systematically quantify the distribution shift between these domains. We introduce a chemically-aware adaptive tokenizer that dynamically balances discretization granularity to preserve spectral semantics while controlling vocabulary size, and an assignment-free peak-aware similarity metric that enables direct comparison between predicted and experimental spectra. Through a unified molecule-to-spectrum paradigm and synergistic coupling of prediction, retrieval, and generation modules, NMRPeak achieves transformative performance on experimental benchmarks: it overcomes the longstanding simulation-to-experiment gap in spectrum prediction while delivering over 95% top-1 accuracy in molecular retrieval and approximately 75% top-1 accuracy in stereochemistry-aware de novo structure generation. These capabilities establish a foundation for automated, high-throughput molecular structure elucidation in organic synthesis, drug discovery, and chemical biology.
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All authors Fanjie Xu, Jinyuan Hu, Jingxiang Zou, Junjie Wang, Boying Huang, Zhifeng Gao, Xiaohong Ji, Weinan E, Zhong-Qun Tian, Fujie Tang, Jun Cheng

Materials Science

Phase behavior and electrical transport in DBTTF-HATCN donor-acceptor mixtures

Andreas Opitz, Hongwon Kim, Dmitry Lapkin et al. (+10 more)

The formation of donor-acceptor complexes (DACs) between the electron donor Dibenzotetrathiafulvalene (DBTTF) and the acceptor Hexaaza\-triphenylene\-hexacarbo\-nitrile (HATCN) results in a new phase with a distinctly different crystal structure as well as new optical absorption bands below the energy gaps of the two pristine materials. X-ray scattering and atomic force microscopy provide detailed insights into the film structure and morphology by systematic variation of the mixing ratio from pristine DBTTF to pristine HATCN. The measured electrical conductivity of thin films depends in a highly non-monotonic manner on the composition of the mixture and shows significantly improved charge transport compared to the pristine films. The temperature-dependent conductivity, charge carrier concentration, and mobility were investigated across these compositions. Surprisingly, all compositions exhibited n-type behavior, except for pristine DBTTF. This behavior is explained by the electronic structure of the mixtures, as revealed by ultraviolet photoelectron spectroscopy, which indicates that charge injection and transport occur via the lowest unoccupied molecular orbital of the DAC and HATCN. Additionally, the observed electrical conductivity is strongly influenced by morphology and structural ordering of the films. These findings offer valuable insights for the design of advanced materials with enhanced electrical performance.
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All authors Andreas Opitz, Hongwon Kim, Dmitry Lapkin, Gianfranco Melis, Ainur Abukaev, Marie Siegert, Lennart Frohloff, Lisa Schraut-May, Oleg Konovalov, Alexander Hinderhofer, Frank Schreiber, Jens Pflaum, Wolfgang Brütting

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

First-principles discovery of stable, anisotropic, semiconducting Sb2X2O (X = S, Se) and Janus Sb2SSeO nanosheets for optoelectronics and photocatalysis

Masoud Shahrokhi and Bohayra Mortazavi

In this work, we conduct a comprehensive first-principles investigation into the design and discovery of novel antimony oxychalcogenide monolayers Sb2X2O (X = S, Se) and Janus Sb2SSeO, examining their structural stability, elastic, electronic, optoelectronic, and photocatalytic properties. Our analysis confirms their thermodynamic and dynamical stability and reveals low cleavage energies, indicating strong feasibility for mechanical exfoliation. The excellent agreement between our HSE06-predicted bandgap of bulk Sb2S2O and experimental measurements further validates the employed computational framework. EWe also find that their optoelectronic responses can be efficiently tuned via biaxial strain, providing a viable route for device-specific property engineering. Favorable band alignments, strong optical absorption, efficient carrier transport, and relatively high dielectric constants collectively support their candidacy for overall water splitting under neutral conditions.These results establish a solid theoretical foundation for the rational design of Sb-based 2D nanostructures and highlight their potential in next-generation direction-dependent optoelectronic and sustainable energy-conversion applications.
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Materials Science

Precipitation induced recrystallisation (PIX) in a Ti-Fe-Mo bcc-superalloy driven by lattice misfit

Neal M. Parkes, Kan Ma, Ben Poole et al. (+2 more)

Beta-Ti bcc-superalloys, comprising an A2 beta-Ti matrix reinforced by ordered intermetallic B2 beta-prime-TiFe precipitates, exhibit an unusual recrystallisation that occurs with no externally applied strain (i.e. no thermomechanical processing). Thermal ageing at 750 degrees Celsius for 72 h results in refinement of the grain size from 364 um to 30 um. This grain refinement is driven by discontinuous precipitation of beta-prime-TiFe lamellae with the beta-Ti matrix from grain/phase boundaries, which is associated with significant misorientation and increased dislocation density, attributed as precipitation induced recrystallisation (PIX).
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All authors Neal M. Parkes, Kan Ma, Ben Poole, Chris Hardie, Alexander J. Knowles