Peer Revenue Publish or profit

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Monday 28 September

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

Enhanced sliding in the coexisting Charge Density Wave phase of strained TbTe3

Antoine Gallo Frantz, Aleksander Sinchenko, Luc Ortega et al. (+5 more)

In the last years, the application of mechanical tensile stress has been shown to trigger unconventional phases in quantum materials. Recently, an orientational transition of the charge density wave (CDW) of TbTe3 was reported under the application of moderate uniaxial tensile stress, associated to the in-plane a/c lattice anisotropy. This leads to the disappearance of the pristine c-oriented CDW (CDWc) and to the appearance of the orthogonal a-oriented one (CDWa). A coexistence phase with a superposition of CDWa and CDWc appears when a=c. Here, we probe the sliding dynamics of both CDWc and CDWa as a function of applied tensile stress, i.e. in the pure CDWc, pure CDWa and coexistence phases, by measuring current-voltage characteristics and associated differential resistances. If the pristine CDWc has been known to display non-linear dynamics and thus sliding for several years, we show here that the strain-induced CDWa phase also displays the same characteristics, proving its incommensurate nature. Moreover, we show that sliding also takes place both for CDWc and CDWa, with reduced threshold currents, in the coexistence phase, which questions the microstructure of these coexisting orthogonal CDWs in real space. Finally, the linearity of the threshold fields is kept for all deformation states, with finite threshold fields at Tc, which is discussed in terms of commensurability and pinning potentials. This work opens new questions for the theoretical description of sliding CDWs in quasi-2D systems.
Read the full abstract

All authors Antoine Gallo Frantz, Aleksander Sinchenko, Luc Ortega, Abdellali Hadj Azzem, Jose Emilio Lorenzo, Pierre Monceau, David Le Bolloch, Vincent Jacques

Materials Science

Magneto-optical Kerr spectroscopy of exciton Rydberg states in a magnetic van der Waals heterostructure

Astha Khandelwal, Benran Zhang, Madhusmita Jena et al. (+8 more)

Excitonic states in two-dimensional semiconductors are sensitive to time-reversal symmetry breaking, yet how interfacial exchange acts on higher-lying exciton Rydberg states remains largely unexplored. Here we show that wavelength-resolved magneto-optical Kerr spectroscopy of a proximity-coupled MoSe$_2$/Fe$_3$GaTe$_2$ van der Waals heterostructure resolves magnetic symmetry breaking across the A- and B-exciton manifolds. Combining reflection, photoluminescence, and photoluminescence excitation spectroscopy with first-principles many-body calculations including screening by the metallic Fe$_3$GaTe$_2$ layer, we assign the strongly enhanced Kerr resonances to the ground and 2s states of both manifolds. Reversing the magnetic field inverts the polarity of every resonance. A field-odd/field-even decomposition confirms a magnetic origin. The opposite Kerr polarities of the A- and B-exciton manifolds can be explained by proximity-induced exchange coupling to the opposite valence-band spins of the two exciton series. Our results establish resonant Kerr spectroscopy as a sensitive probe of magnetically induced symmetry breaking across the excitonic manifold.
Read the full abstract

All authors Astha Khandelwal, Benran Zhang, Madhusmita Jena, Zhenchao Wen, Kenji Watanabe, Takashi Taniguchi, Saroj P. Dash, Zhenglu Li, Ryo Kitaura, Bhagwati Prasad, Daichi Kozawa

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

Electronic and topological properties of Ce-based honeycomb ferromagnet Ce$_2$Zn$_6$Ge$_3$

Yanen Huang, Zihan Yang, Jiawen Zhang et al. (+7 more)

Ce$_2$Zn$_6$Ge$_3$ is a rare example of the Ce-based honeycomb ferromagnet. Here, we report its Fermi surface and topological properties by quantum oscillations via the magnetoresistance and tunnel diode oscillator (TDO) based measurements, in combination with the density functional theory (DFT) calculations. Four fundamental frequencies are observed in the quantum oscillations, and their angle dependence is more compatible with the DFT calculations assuming that the 4$f$-electrons are localized, suggesting a localized nature of ferromagnetism in Ce$_2$Zn$_6$Ge$_3$. Furthermore, the observations of negative longitudinal magnetoresistance and non-zero Berry phase, as well as the existence of two pairs of Weyl points near the Fermi level as revealed from the calculated electronic structures, provide strong evidence for nontrivial topology in Ce$_2$Zn$_6$Ge$_3$. These findings suggest that Ce$_2$Zn$_6$Ge$_3$ could provide a unique platform to study magnetism, topology, quantum criticality and their interplay.
Read the full abstract

All authors Yanen Huang, Zihan Yang, Jiawen Zhang, Yuwei Zhou, Lubin Wang, Gang Li, Michael Smidman, Chao Cao, Yu Liu, Huiqiu Yuan

Materials Science · Cross-listed from cond-mat.dis-nn

Pre-registered tests of solid-state-physics-inspired LLM compression: a cluster-level negative result at small-language-model scale

Jun-qiang Lu

We report a three-month autonomous research-agent program testing five solid-state-physics-inspired compression mappings on pretrained language models, with predictions committed to git before any pilot data and a 3-sigma gate deciding PASS or SHELVE. The common anchor – area-law / Kohn-nearsighted decay of the one-particle density matrix – has a distance face (P001 Wannier, P002 tight-binding) and a rank face (P003 DMRG-truncated MLPs, P005 Wilson-RG, P011 tensor-train embeddings). P005 was pre-empted at Phase 1; three of four Phase-3 pilots were falsified. On the attention face, GPT-2-medium attention-versus-distance is best fit by a stretched exponential in 12 of 16 median-layer heads once probe padding is excluded, and a tight-binding cutoff costs +96% perplexity (P002); on Pythia-160M the Wannier sparsity 0.054 +/- 0.004 is indistinguishable from PCA, random-Haar and identity baselines (P001). On the rank face, per-token tensor-train bond dimension does not track surprisal (r = 0.016 vs a pre-registered 0.65) and the format inflates rather than compresses (P011). P003 is mixed: its scaling claim shelved (r = -0.434), its MPO premise died at stage-0, and its cross-paper check, r = 0.523 as first written, collapses to 0.047 under the same correction, leaving both cross-paper checks null. The results invert the pre-registered prediction that most attention heads behave like Kohn-nearsighted insulators, pointing instead to critical, glassy or heavy-tailed regimes; the inversion is specific to the <= 350M scale tested, while the rank-face no-gain result held to 7-8B. We contribute the pre-registration + 3-sigma + cluster-framing + append-only-catalogue discipline – including why our own enforcement gate was designed but not deployed – four pre-registered negative results with full data release, and the inversion. The catalogue holds eighteen concluded studies, seventeen negative.
Read the full abstract

Materials Science

Finite-temperature grain boundary phases, transformations, and diagrams in alloys

Flynn Walsh and Timofey Frolov

Current understanding of alloy grain boundaries is limited by the incompleteness of atomistic simulation techniques, which either neglect entropy or artificially constrain the atomic density. This study introduces Monte Carlo simulations that simultaneously sample all the microscopic degrees of freedom in complex interfaces: position, configuration, and atom number. The method enables rigorous predictions of finite-temperature grain boundary structures, phase transformations, and diagrams in multicomponent materials. Simulations of W-V alloys demonstrate the necessity of the approach by uncovering a range of previously inaccessible phase transitions including condensation of interstitial solutes and transformation of dislocation structure.
Read the full abstract

Materials Science · Cross-listed from physics.optics

Stimulated Electro-optic Scattering

Violet Workman and Gaurav Bahl

Stimulated Brillouin Scattering (SBS) couples light to acoustic waves and underpins applications ranging from sensing and signal processing to quantum photonics. In solids, this interaction is generally attributed to photoelasticity and the motion of dielectric boundaries. Here we show that piezoelectricity opens an additional, previously unrecognized pathway that can substantially reshape Brillouin gain. This contribution arises from the combined action of linear electro-optic “Pockels” scattering and its reciprocal $\chi^{(2)}$-mediated optical drive, which couple optical fields to the electric fields that accompany mechanical motion in piezoelectrics. We formally incorporate these effects into the modern theory of SBS and apply it to monolithic lithium niobate waveguides. In addition to large enhancement and suppression of the Brillouin gain, we surprisingly find occurrences of large gain where conventional theory would otherwise have predicted zero Brillouin interaction. These instances are the first identification of purely electro-optic SBS, a process we term stimulated electro-optic scattering, as it only involves interactions between electromagnetic fields even though a mechanical excitation is present. Our results establish the electro-optic tensor as a key governing parameter for Brillouin interactions in piezoelectric media and provide a new degree of freedom for engineering photon-phonon coupling independent of photoelasticity and index contrast.
Read the full abstract

Materials Science

Nanometer-scale operando electric field mapping in oxide junctions by correlative STEM-EBIC and 4D-STEM

Yining Xie, Eoin Moynihan, Xingyao Li et al. (+5 more)

Understanding local electric fields at oxide interfaces is essential for linking interfacial electrostatics to device functionality, yet conventional electrical measurements infer these fields only indirectly. Here, we combine operando scanning transmission electron microscope electron-beam-induced current (STEM-EBIC) with four-dimensional-STEM (4D-STEM) to quantitatively reconstruct the bias-dependent electric field spatial distribution across an oxide Schottky junction at nanometer scale. Using La0.67Sr0.33MnO3/Nb:SrTiO3 (LSMO/NSTO) as a model system, we fabricate an electron-transparent junction on a MEMS biasing platform and verify that it retains the rectifying transport behavior. STEM-EBIC provides complementary information addressing several key limitations in quantitative 4D-STEM field mapping for heterojunctions. The reconstructed electric field profiles show a pronounced nonlinear decay within the depletion region and an extended penetration into the LSMO. These results directly reveal the deviations of oxides Schottky junction from the ideal conventional Schottky depletion model, providing experimental signatures of non-classical interfacial electrostatics. Our correlative approach enables quantitative nanoscale electric field mapping in operating oxide heterojunctions, providing a basis for linking interfacial electrostatics to macroscopic transport and guiding oxide devices design.
Read the full abstract

All authors Yining Xie, Eoin Moynihan, Xingyao Li, Richard Beanland, Aditya Singh, Marin Alexe, Mingmin Yang, Ana Sanchez

Materials Science

Native implementation of the machine-learned Skala exchange-correlation functional in CP2K: Unified one-centre reconstruction for molecular and condensed-phase calculations

Johann Pototschnig, Franz Pöschel, Jürg Hutter et al. (+1 more)

We implement the machine-learned Skala exchange-correlation (XC) functional natively in CP2K using its Gaussian and plane-wave (GPW) and Gaussian and augmented-plane-wave (GAPW) methods. A joint one-centre reconstruction of density, density gradients, and kinetic-energy density before functional evaluation preserves mixed gradient terms and nonlocal couplings between smooth and atom-local contributions in all-electron and pseudopotential calculations. An XC-specific GAPW representation resolves rapidly varying local contributions on atom-centred grids, reducing plane-wave requirements for pseudopotential calculations. The implementation includes Brillouin-zone sampling and point-group symmetry reduction. With sufficiently flexible orbital bases, it retains the molecular benchmark accuracy of our earlier GauXC formulation. All-electron Skala-D3(BJ) calculations yield a mean absolute error (MAE) of 1.54 kJ mol$^{-1}$ against diffusion Monte Carlo for crystalline CO$_2$, NH$_3$, and urea, spanning dispersion, quadrupolar electrostatics, and hydrogen bonding. For all thirteen DMC-ICE13 phases, the MAEs are 1.16 kJ mol$^{-1}$ for absolute lattice energies and 0.82 kJ mol$^{-1}$ for the twelve relative energies to ice Ih. At fixed experimental geometries, all-electron/mixed-core calculations give a band-gap MAE of 0.43 eV on a 15-material set, substantially below commonly used semilocal functionals and comparable to widely used hybrid functionals. The LC10 benchmark nevertheless reveals systematically underestimated equilibrium lattice constants, indicating structural overbinding. This framework connects molecular Skala to condensed-phase electronic structure and enables future development using periodic many-body reference data.
Read the full abstract

All authors Johann Pototschnig, Franz Pöschel, Jürg Hutter, Thomas D. Kühne

Sunday 27 September

Materials Science

Correlation Between Dopant Atom Evaporation Field and Measured Site Preference in Atom Probe Tomography

Kasper A. Hunnestad, Constantinos Hatzoglou, Frida H. Danmo et al. (+6 more)

Complex oxides possess a wide range of electric, magnetic, and optical properties that can be precisely tuned by chemical doping. The atomic-scale analysis of the property-controlling dopants, however, becomes increasingly difficult towards low doping levels. Atom probe tomography (APT) offers chemical sensitivity and spatial resolution to image individual dopant atoms down to a few parts per million. To reliably extract such information, detailed knowledge about the atom-specific field evaporation processes is required. Here we demonstrate a first insight into the APT-measured atomic position of dopant atoms and the field evaporation conditions, using Zr-doped ErMnO3 as a model system. Our analysis reveals a substantial preferential retention of both matrix and dopant atoms which strongly affects the dopant site determination and can lead to an incorrect interpretation. The retention effect is determined by intrinsic and extrinsic parameters, such as the dopant's evaporation field and concentration and the analysis temperature, respectively, as we explain based on field-evaporation simulations. Our results are important for the APT-based analysis of individual dopant atoms in solid systems and the understanding of field evaporation dynamics at the atomic level in general.
Read the full abstract

All authors Kasper A. Hunnestad, Constantinos Hatzoglou, Frida H. Danmo, Zewu Yan, Edith Bourret, Francois Vurpillot, Antonius T. J. van Helvoort, Sverre Selbach, Dennis Meier

Materials Science

Democratizing Atomistic Simulation Workflows for the AI Era with the Quantum Accelerator

Andrew S. Rosen, Naisargi Goyal, Brad Ayers et al. (+25 more)

We present the Quantum Accelerator (QuAcc), an open-source workflow library for atomistic simulations with an emphasis on quantum-mechanical calculations. QuAcc provides predefined workflow recipes spanning first-principles electronic-structure methods, semiempirical and tight-binding approaches, classical potentials, and foundation machine-learned interatomic potentials (MLIPs). A central design feature of QuAcc is its separation of domain-specific scientific logic from the workflow engine used to orchestrate and execute calculations. Workflows are written as ordinary Python functions and can be executed with multiple supported workflow engines without modifying the underlying source code, lowering the barrier to developing and contributing new workflows. QuAcc also streamlines the evaluation of foundation MLIPs by providing a unified platform for generating ab initio reference calculations consistent with the model of interest, mitigating methodological drift when assessing model performance. Together, these features make QuAcc a flexible and accessible framework for atomistic simulation workflows that have become central to the current era of machine learning and artificial intelligence.
Read the full abstract

All authors Andrew S. Rosen, Naisargi Goyal, Brad Ayers, Vineet Bansal, Julia H. Baratta, Samuel M. Blau, Yuan Chiang, Sihoon Choi, Orion Archer Cohen, Blake Dallmann, Tom Demeyere, Will Engler, Yue-Wen Fang, Isabella Furrick, Eliu Huerta, Honghui Kim, Hironori Kondo, Anup Kumar, Jaehong Kwon, Osman Mamun, Charles B. Musgrave III, Hananeh Oliaei, Aryan Saha, Davide Sarpa, Benjamin X. Shi, Yuliang Shi, Xing Wang, Robert B. Wexler

Materials Science

Benchmark of First-Principles Titanium K-Edge X-Ray Absorption Spectral Simulations on Titanium-containing Oxides

Chuntian Cao, Joshua J. Kas, Karol Dyro et al. (+3 more)

X-ray absorption spectroscopy (XAS) is a powerful, element-specific probe for investigating the local structural and electronic properties of materials. However, quantitative analysis remains challenging, necessitating accurate first-principles spectral simulations. In this study, we benchmark first-principles simulations of Ti K-edge X-ray absorption near-edge structure (XANES) against experimental data for nine common titanium compounds. We systematically investigate key physical effects, including quadrupole excitations, thermal disorder, and many-body shake-up. Our results demonstrate that quadrupole excitations and thermal disorder are essential for capturing accurate pre-edge features, while many-body shake-up effects significantly influence the spectral shape of the main- and post-edge regions. By incorporating these effects alongside a band-theory treatment of the core-hole final state, our simulated spectra achieve excellent agreement with experimental data for most of the systems, as evidenced by high similarity scores. The shoulder peak in BaTiO$_3$ at 4980 eV in the experiment is largely missing in simulation. Further analysis shows that more accurate electronic structure theory than semi-local density functional theory is required to capture the correlation effects of the Ba $4f$ orbitals and that defects, such as oxygen vacancies, may also contribute to the shoulder. Beyond tackling specific titanium material systems, this work establishes a robust workflow for generating high-fidelity Ti K-edge XANES databases for titanium compounds, providing a framework that can be generalized to a broad range of materials.
Read the full abstract

All authors Chuntian Cao, Joshua J. Kas, Karol Dyro, Bruce Ravel, John Vinson, Deyu Lu

Materials Science

Placement-driven reversal of preferred spin alignment in monolayer hBN vacancy pairs

Daniel Hashemi

The negatively charged boron vacancy is an optically addressable spin centre in hexagonal boron nitride (hBN), but bringing two vacancies together introduces electronic interactions absent from the isolated-defect picture. Here we use density-functional theory at total charge q = -2 to show that atomic-scale placement reverses the preferred collinear spin alignment in monolayer hBN. Among seven configurations, the closest pair, separated by 4.3 angstrom, favours parallel alignment by 27.6 meV within the semilocal approximation. Moving one vacancy by a single lattice vector reverses the preference, and a 7.5 angstrom pair favours antiparallel alignment by 50.7 meV. Numerical controls change these two reference splittings by less than 1 meV; hybrid-functional calculations retain their signs while substantially changing their magnitudes. Local distortions connect the antiparallel preference at 7.5 angstrom to changes in vacancy-state hybridization along an intervening atomic chain. The closest pair instead exhibits a contact-localized spin-density contrast and constrained angular energies that depart from the bilinear Heisenberg form. These results identify a placement-sensitive regime of interacting defects and provide a microscopic foundation for investigating coupled spin centres in atomically thin materials.
Read the full abstract

Materials Science

Computational symmetry hierarchy of time-reversal-even and -odd spin Hall conductivity tensors in altermagnets

Dameul Jeong, Seoung-Hun Kang and Young-Kyun Kwon

Predicting the full spin Hall conductivity tensor of a magnetic crystal is difficult because crystallographic and magnetic symmetries do not constrain all parts of the response in the same way. Here, we separate the spin Hall conductivity of altermagnets into time-reversal-even and time-reversal-odd channels and combine symmetry analysis with first-principles calculations for six representative compounds spanning distinct crystallographic classes. The even channel follows crystallographic selection rules consistent with its Berry-curvature Fermi-sea origin. The odd channel is set by magnetic symmetry and can be reshaped by antiunitary operations whose spatial parts originate from screw or glide symmetries. Momentum-resolved analysis further links the even response to spin-orbit-driven avoided crossings and the odd response to anisotropic near-Fermi-level spin-current response textures. By converting crystallographic and magnetic symmetry operations into linear constraints on the full 27-component SHC tensor, this framework provides a computational prescreening route for identifying symmetry-allowed spin Hall channels before dense first-principles transport calculations. Extending the same analysis to 62 spin-split collinear antiferromagnets yields a magnetic-point-group tensor atlas, identifying design limits such as the complete 13/14tensor partition in CuF2 and the one-parameter time-odd tensor compression in MnSe.
Read the full abstract

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

Accelerating Quantum Simulations of Materials Through Parameter and Ansatz Transfer Strategies

Saurabh Shivpuje, Vinit Singh, Manas Sajjan et al. (+1 more)

Quantum computing offers a promising route for electronic-structure calculations, but practical condensed-matter applications often require solving large families of related Hamiltonians arising from $\mathbf{k}$-point sampling, compositional variation, defects, and changes in system size. Here, we develop strategies for transferring variational information between related Hamiltonians to accelerate quantum simulations. For Hamiltonians of the same embedded size, optimized variational parameters are transferred between related calculations. For different sizes, we introduce Augmented Ansatz Reuse for Target Initialization (AARTI), which transfers compatible Pauli-generator structure and optimized source parameters, then augments the ansatz with target-specific generators. Our workflow combines density functional theory, Wannier downfolding, embedded tight-binding Hamiltonians, variational quantum algorithms, and neural-network quantum states, with quantum-circuit simulations implemented using NVIDIA's CUDA-Q platform. Using Li$_x$CoO$_2$ as a representative battery cathode material, we study Hamiltonian families spanning multiple delithiation levels, dense $\mathbf{k}$-point meshes, and increasing sizes. Parameter and ansatz transfer substantially reduce the optimization steps required to solve these related Hamiltonians while maintaining the common target accuracy, with lower terminal errors in several cases. The calculated electronic-structure evolution with delithiation exhibits pronounced non-rigid-band behavior consistent with experiment. These results establish a framework for exploiting similarity among related Hamiltonians to improve the efficiency and scalability of quantum workflows for realistic condensed-matter systems.
Read the full abstract

All authors Saurabh Shivpuje, Vinit Singh, Manas Sajjan, Sabre Kais

Materials Science

Toward catalyst-mediated growth of diamond and cubic boron nitride wires

Rodney S. Ruoff

A reproducible method for sustained catalyst-mediated growth of diamond and cubic boron nitride (cBN) wires has yet to be established. Catalyst-assisted growth has produced carbon and boron nitride nanotubes and a wide range of elemental, compound and alloy nanowires. Diamond and cBN wires could combine high specific stiffness and strength with heat conduction and electrical insulation. I propose vapor-liquid-solid (VLS) and vapor-solid-solid (VSS) routes in which temperature, feed, catalyst or starting contact changes between formation of the first diamond or cBN segment and its continued growth. The approaches include switching from carbide or boron-rich starter wires, depositing catalyst on selected facets of existing crystals, and using local solid feedstock to supply the catalyst during initial growth. Historical diamond-whisker reports motivate renewed tests of diamond-metal contacts. The proposed experiments ask whether these contacts can favor tetrahedral bonding while maintaining a supply of atoms to the growing wire. Both single-crystal and polycrystalline products, from nanometer to micrometer and larger diameters, are of interest.
Read the full abstract

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

Bare-Die Antiferromagnetic Computing

Yu Liu, Zhuoting Han, Zexin Feng et al. (+15 more)

Semiconductor electronic devices are increasingly constrained by fundamental quantum tunneling effects and charge-based mechanisms, which severely limit further miniaturization, write-speed scaling, and environmental robustness of silicon-based technologies. These limitations are particularly prohibitive for deep-space exploration, where extreme temperatures, ultra-strong magnetic fields, and intense radiation rapidly incapacitate conventional electronics without massive shielding. Here, we present an intrinsically resilient, strain-mediated antiferromagnetic MnIr/PMN-PT edge processor that operates reliably as a bare die under temperatures up to 500 K, magnetic fields of 55 T, and radiation doses of 1.5 Mrad. By exploiting an input-modulated in situ self-refreshing encoding mechanism, the device performs nonlinear feature extraction and classification directly from raw analog signals, enabling an analog computing architecture that requires no time-frequency transformation. This architecture achieves 99.8% accuracy in speech recognition without digital preprocessing and 100% accuracy in astronaut visual object recognition. Furthermore, an all-hardware integrated drone vision system demonstrates real-time in situ command execution and autonomous navigation, delivering a terahertz-level response frequency and an ultra-low energy consumption of approximately 0.2 fJ per operation. This work expands the functional scope of antiferromagnetic devices beyond memory and logic, establishing them as a promising materials platform for energy-efficient physical computing and autonomous intelligence in extreme environments.
Read the full abstract

All authors Yu Liu, Zhuoting Han, Zexin Feng, Peixin Qin, Zhiyuan Duan, Yuhao Ye, Zengwei Zhu, Chengyan Zhong, Li Liu, Guojian Zhao, Wenbin Shen, Jingyu Li, Sixu Jiang, Xiaoyang Tan, Xiaoning Wang, Ziang Meng, Chengbao Jiang, Zhiqi Liu

Materials Science

Temperature Periodic Modulation Doubles the Power Output of Thermoelectric Generators

Dario Narducci, Antonio Mazzacua and Federico Giulio

Thermoelectric heat harvesting provides in principle a flexible, reliable way to convert heat into electric energy, thus recovering waste heat and powering off-net devices. However, thermoelectricity conversion efficiency is still low, despite the major efforts deployed over the last two decades to improve materials performances. A largely unexplored opportunity to increase harvesting efficiency is offered by converting heat flux dynamically. It was shown [D. Narducci et al., Mater. Today Phys. 54, 101713 (2025)] that when the temperature of the heat source is sinusoidally modulated, this leads to an increase of the maximum power by up to 50 %. In this paper we show how this approach can be further and significantly enhanced. We found that sinusoidal modulation can be outperformed by a different periodic modulation, leading to an increase of the power output by up to 100 % compared to the stationary case. Furthermore, we extended our analyses beyond the constant-property approximation, showing that the power output enhancement is robust, applying to any real material where the temperature dependence of all phenomenological coefficients is accounted for. This major power output enhancement offers a novel, immediately applicable pathway to overcome the efficiency limits of thermoelectric devices.
Read the full abstract

Materials Science

Let CSP Be Your ANCHOR: Adaptive Crystal Search over Frozen Structure Priors

Emma Lei Hovmand, Jonas Elsborg, Melih Kandemir et al. (+1 more)

De novo crystal generation (DNG) models decide where to search in composition space and how to generate structures with one set of weights. We argue that discovery is better served by separating the two. A crystal structure prediction (CSP) model is a physical prior that should be improved by likelihood training, while rewards, including novelty measured against the search's own history, should act on a search over compositions. We introduce ANCHOR, a GRPO composition policy trained with multi-objective rewards around a frozen CSP model, and continuous adaptive novelty (CAN), a graded novelty score against known structures and a growing discovery history. Using the frozen CSP model as a fixed ruler under one evaluator, we test where adaptation should act. Replacing DNG compositions with ANCHOR's policy on the same CSP backbone raises MSUN from 11.4% to 47.6% and SUN from 1.1% to 22.1% at 99.9% formula uniqueness. Fine-tuning DNG models directly on the same rewards instead moves their composition marginal without raising their on-hull fraction. We show that KL-regularized fine-tuning of a DNG model can only reweight chemistry the pretrained model already supports by a bounded factor, while unregularized DNG fine-tunes move toward known or less stable chemistry. Even a stability-only reward routed into ANCHOR's CSP backbone roughly halves SUN relative to the frozen backbone, whereas likelihood training on structures found during search can improve a CSP backbone. Under MatterGen's evaluation pipeline, ANCHOR raises state-of-the-art MSUN from 29.2% to 41.3%, transfers without retraining to two further CSP backbones, and reaches 47.1% after distillation into Crystalite-CSP. As with any model optimised against a potential, its on-hull rate depends on that potential.
Read the full abstract

All authors Emma Lei Hovmand, Jonas Elsborg, Melih Kandemir, Arghya Bhowmik

Materials Science

Low-temperature thermal expansion of the $\alpha$ and $\omega$ phases of titanium

Norimasa Nishiyama, Atsushi Togo and Yoshitaka Matsushita

We investigated the low-temperature thermal expansion of the $\alpha$ phase and the $\omega$ phase, a high-pressure polymorph of titanium, by X-ray diffraction measurements from approximately 5 to 300 K, together with first-principles calculations. Single-phase bulk polycrystalline $\omega$-Ti was synthesized at 7.7 GPa and 500 $^\circ$C and recovered to ambient pressure. Although the two phases exhibit very similar volumetric thermal expansion, their axial responses are markedly different. In $\alpha$-Ti, the $c$-axis thermal expansion coefficient becomes negative below approximately 50 K and reaches a minimum of $-0.71 \times 10^{-6}$ K$^{-1}$ at 20 K. Both experiment and theory indicate substantially smaller $c$-axis negative thermal expansion than previously reported from single-crystal length measurements. In contrast, $\omega$-Ti expands nearly isotropically along the $a$ and $c$ axes, and its $c/a$ ratio remains nearly temperature independent and close to the ideal bcc-derived value. The $c$/$a$ ratio of $\alpha$-Ti decreases with increasing temperature. Debye-Grüneisen analysis yielded Debye temperatures of $427 \pm 5$ K and $409 \pm 12$ K and effective Grüneisen parameters of $1.33 \pm 0.04$ and $1.23 \pm 0.04$ for $\alpha$-Ti and $\omega$-Ti, respectively. The first-principles calculations reproduce the volumetric thermal expansion of both phases and capture the overall trends of their axial responses.
Read the full abstract

Materials Science

Symmetry-guided Design Principles for Spin Splitting and Hall Transport in Orthorhombic Altermagnetic Perovskites

Rasmita Kumari, Bishal Das and Aftab Alam

Magnetic symmetry can generate momentum-dependent spin-split electronic bands even in the absence of spin-orbit coupling (SOC), giving rise to the recently discovered class of altermagnets. Here, we establish a unified symmetry framework for collinear antiferromagnets in orthorhombic Pbnm perovskites by combining spin and magnetic group theory with first-principles calculations. We show that the irreducible representation of the magnetic order uniquely determines the momentum-space planes supporting altermagnetic spin splitting, the form of the effective low-energy Hamiltonian, the orientation of SOC-induced weak ferromagnetic canting, and the allowed anomalous Hall conductivity (AHC) tensor components. These predictions are validated in eight experimentally realized orthorhombic perovskite oxides spanning both insulating and metallic regimes. In particular, LaTiO3 and CaCrO3 exhibit sizable anomalous Hall conductivities of approximately 38 and 205 S/cm, respectively, despite nearly vanishing net magnetization. We further show that SOC gaps symmetry-protected altermagnetic band crossings, generating large Berry curvature, while the Hall response is fundamentally rooted in the underlying non-relativistic spin splitting. Our work establishes a predictive symmetry-based framework for discovering and engineering altermagnetic materials with tunable spin-dependent electronic and transport properties.
Read the full abstract

Materials Science

Unveiling Lattice Dynamics and a Hidden Structural Transition in the 2D Ferromagnet AgVP$_2$Se$_6$ via Raman Spectroscopy

Thi Hai Yen Pham, Po-hao Chang, Aidan C. Malloy et al. (+7 more)

Transition-metal chalcophosphates (TMCs) are two-dimensional (2D) van der Waals materials supporting a broad range of electronic and magnetic properties. Among quaternary TMCs, AgVP$_2$Se$_6$ is a rare ferromagnet (FM) with a triangular V sublattice, in contrast to the antiferromagnetic (AFM) zigzag chains of the sulfide AgVP$_2$S$_6$. Prior Raman studies of AgVP$_2$Se$_6$ have been performed far above the Curie temperature ($T_C$), preventing studies of spin-phonon coupling. Here, we report polarization-resolved, temperature-dependent Raman and magneto-Raman spectroscopy of AgVP$_2$Se$_6$ single crystals grown by chemical vapor transport (CVT) and flux methods, across the FM transition, complemented by density functional theory (DFT) calculations of phonon, optical and magnetic properties. Cryogenic Raman spectra resolve up to thirty peaks, while angle-resolved measurements enable their symmetry assignment. Spectral differences between CVT- and flux-grown crystals are traced back to the presence of different interlayer stacking domains in these samples. Temperature- and field-dependent Raman spectra remain largely unchanged across $T_C$, suggesting weak spin-phonon coupling. However, pronounced spectral alterations near 100 K suggest a potential structural phase transition. Our DFT calculations further reconcile the large discrepancy between the transport activation gap ($\approx$ 0.325 eV) and optical absorption edge ($\approx$ 2.14 eV), attributing the former to a transition to the V-d upper Hubbard band that is optically dark but thermally accessible. We also suggest a theoretical explanation of the qualitative difference (reproduced by DFT calculations) between the magnetic properties of the sulfide and selenide. These results provide key information regarding the lattice dynamics of AgVP$_2$Se$_6$ and will guide future applications in spin-based electronics.
Read the full abstract

All authors Thi Hai Yen Pham, Po-hao Chang, Aidan C. Malloy, Seng Huat Lee, Zhiqiang Mao, Maria F. Munoz, Riccardo Torsi, Angela R. Hight Walker, Igor Mazin, Patrick M. Vora

Materials Science

Unifying Magnetic, Electrical, and Thermoelectric Responses in a Non-Collinear Antiferromagnet

André José, Adrielson Dias, Carlos Eduardo et al. (+6 more)

Non-collinear antiferromagnets offer unconventional routes for controlling magnetic, electrical, and thermoelectric responses through their complex spin configurations and interfacial symmetry. Here, we detect exceptional interfacial properties arising from a non-collinear antiferromagnet by demonstrating a robust and quantitatively consistent exchange-bias response in an IrMn$_3$/Py heterostructure. The system consists of a 10 nm IrMn$_3$ layer coupled to a 5 nm permalloy (Py) film. Longitudinal magneto-optical Kerr effect (MOKE), anisotropic magnetoresistance (AMR), and anomalous Nernst effect (ANE) measurements independently reveal the same unidirectional field shift of approximately 50 Oe, together with a consistent cosine angular dependence. The simultaneous observation of these signatures establishes a direct correspondence between the interfacial magnetic symmetry imposed by the non-collinear antiferromagnet and the responses of the adjacent ferromagnet. This symmetry is manifested consistently in magnetization reversal, charge transport, and thermally driven voltage generation, demonstrating that the exchange-bias imprint is not restricted to a single experimental observable. Our results reveal a coherent multifunctional response of IrMn$_3$/Py and extend the conventional understanding of exchange bias beyond collinear antiferromagnetic systems. More broadly, they demonstrate the potential of non-collinear antiferromagnets as platforms for coupling magnetic, electrical, and thermoelectric functionalities in spintronic and spin-caloritronic devices.
Read the full abstract

All authors André José, Adrielson Dias, Carlos Eduardo, Giovanna Celly, Luiza Paffer, José Araújo, José Laurentino, Monalisa Cavalcante, José Holanda

Saturday 26 September

Materials Science

Piezo-Hall effect in $\mathrm{RbCr_2Se_2O}$

San-Dong Guo, Shi-Hao Zhang and Feng-Ren Fan

The anomalous Hall effect (AHE) is of fundamental importance for understanding spin-orbit coupling and magnetic transport in magnetic materials. Meanwhile, strain can significantly modify material properties, and the piezoelectric effect stands as a well-known representative. The piezo-Hall effect combines the two physical ingredients of AHE and strain. Specifically, the piezo-Hall effect describes a physical process in which the magnetic space group (MSG) of a magnetic material prohibits a net magnetic moment and suppresses the AHE in the pristine state but transforms into a new MSG upon strain application that permits a net magnetic moment, thereby enabling the emergence of the AHE. The underlying mechanisms cover strain-induced magnetic electronic state transition and strain tuning of magnetization direction. We take the $d$-wave altermagnetic metal as an example to analyze the piezo-Hall effect in detail, with first-principles calculations carried out on the specific material $\mathrm{RbCr_2Se_2O}$ to verify this scenario. A notable result is that under identical uniaxial strain applied along the $x$ and $y$ directions, the anomalous Hall conductivity exhibits opposite signs but equal magnitudes. Similarly, the piezo-magneto-optical effect can also be proposed, and if strain tuning is replaced by electric-field modulation, the electro-Hall effect and electro-magneto-optical effect can be also put forward accordingly. Even temperature can serve as an external field to introduce the temperature Hall effect. Our work advances the understanding of the coupling between strain and physical properties.
Read the full abstract

Materials Science

Impact of Phonon-Magnon Scattering on Thermal Transport across Antiferromagnetic and Ferromagnetic Oxides

Zeyu Xiang and Bolin Liao

Phonon–magnon coupling has been extensively studied in ferromagnets, whereas its microscopic mechanisms in antiferromagnets remain less understood. Here, we combine first-principles calculations with spin–lattice dynamics to investigate phonon–magnon interactions and their impact on thermal transport in antiferromagnetic NiO and MnO, which are put in contrast to the ferromagnetic EuO with an identical crystal structure. Green–Kubo and spectral energy density analyses show that spin dynamics reduce phonon thermal conductivity and lifetimes, with the strongest effects in MnO. Comparison of the excitation spectra indicates that spin-induced phonon scattering depends sensitively on the relative phonon and magnon energy scales, while the contrasting behavior of MnO and EuO further highlights the role of magnetic order. A simplified phase-space model further illustrates that, for comparable phonon and magnon energy scales, the antiferromagnetic case can support a larger phonon–magnon scattering phase space than the ferromagnetic case, suggesting a greater number of kinematically allowed scattering channels. These results identify excitation energy scales and magnetic order as key factors governing phonon–magnon scattering in magnetic materials.
Read the full abstract

Materials Science

Parity-selected Bethe-Salpeter equation: symmetry-adapted regularization of the exciton-phonon self-energy in polar semiconductors

Michael O. Atambo

Finite-temperature Bethe-Salpeter calculations of exciton-phonon self-energies in polar materials are bottlenecked by the Fröhlich divergence of the intra-1s scattering vertex. We show that for a bound electron-hole pair this divergence is analytically eliminated by electron-hole interference: the intra-1s vertex admits the exact factorization $V_{\mathrm{el}}(q)=q\,\mathcal G(q)$ with $\mathcal G(0)\propto(m_h-m_e)/(m_h+m_e)$, vanishing identically for equal masses (parity protection). A multipole interference factor $\mathcal I_n=\beta_e^{\,n}-(-\beta_h)^{n}$ determines where the singularity survives-only in dipole-allowed inter-state channels. We formulate a parity-selected truncation of the exciton-phonon self-energy in which the intra-1s channel is evaluated exactly at negligible cost, converging with $10^2$-$10^3$ fewer $q$-points. We find that the regularized intra-1s channel, previously obscured by numerical cutoffs, controls the temperature-dependent exciton shift in mass-asymmetric polar semiconductors.
Read the full abstract

Materials Science

Composition-Driven Metal-to-Semiconductor Transition and Enhanced Phonon Transport in B-C substituted Clathrate

Ghulam Hussain, Dario Massa, Rajibul Islam et al. (+3 more)

Establishing chemical design rules that simultaneously control the electronic structure and thermal transport is a long-sought goal for heat-management and energy materials. Here, we demonstrate that a single B-to-C substitution changes the electron count and simultaneously reconstructs the bonding network and crystal structure, driving a metal-to-semiconductor transition while concurrently enhancing the lattice thermal conductivity. Using density-functional theory (DFT) and machine-learned interatomic potentials (MLIPs), we investigate the electronic structure, lattice dynamics, and phonon thermal transport in cubic BaB3C3 and its B-to-C-substituted tetragonal BaB2C4 structure. The substitution donates one electron per formula unit to the B-C framework, thereby triggering the formation of strong C-C bonds and opening a bandgap of 0.33 eV. The Message Passing Atomic Cluster Expansion (MACE) model reproduces DFT energies and forces, yielding phonon dispersion and lattice thermal conductivity in excellent agreement with DFT benchmarks. Thermodynamically stable cubic BaB3C3 possesses an isotropic lattice thermal conductivity of 7.6 W/mK at 300 K. Substituting B with C hardens the phonon dispersion (evidenced by a frequency upshift from ~800 to ~900 cm^-1) and simultaneously boosts both phonon group velocities and lifetimes. Consequently, the lattice thermal conductivity surges to 18.7 W/mK, representing a remarkable ~2.5-fold enhancement of the in-plane component and a transformation from isotropic to anisotropic behavior, characterized by kappa_x = kappa_y > kappa_z. Our results demonstrate that minimal B-to-C substitution provides a viable strategy to modulate the electronic structure, thereby transforming the crystal from a metal to a semiconductor and concomitantly enhancing phonon thermal transport.
Read the full abstract

All authors Ghulam Hussain, Dario Massa, Rajibul Islam, Magdalena Birowska, Carmine Autieri, Xiaoguang Li

Materials Science

Digital Etching of Single-Crystalline Silicon Fin Barriers Down to Sub-10 nm

Yu Wu, Teun A. J. van Schijndel, Anthony P. McFadden et al. (+3 more)

This work presents a fabrication process to realize sub-10 nm-thick, high-aspect-ratio Si fins using high-resistivity float-zone single-crystal Si wafers. Following anisotropic wet etching, a digital etching process based on repeated rapid thermal annealing (RTA) oxidation and vapor-phase hydrofluoric acid (VHF) etching of the resulting oxide was developed, enabling thinning of Si fins into the sub-10 nm regime. Cross-sectional scanning transmission electron microscopy confirms fin thicknesses as thin as 6 nm, although with a tapered profile resulting from the initial anisotropic wet etch. Tapering of the fin was reduced by using an N{_2}/O{_2} (5:1) ambient together with a reduced ramp rate during the temperature ramping for the RTA oxidation process. A thickness variation of 3 nm along a 1.2 {\mu}m tall fin was achieved on a fin with 12 nm near the top and 15 nm near the base. The developed process provides a pathway for fabricating Josephson junctions, setting a foundation toward reproducible and scalable superconducting qubit fabrication with single-crystal Si dielectric barriers using readily available Si processing technology.
Read the full abstract

All authors Yu Wu, Teun A. J. van Schijndel, Anthony P. McFadden, Wilson J. Yánez-Parreño, Raymond W. Simmonds, Christopher J. Palmstrøm

Materials Science

Phase-selective growth of water-soluble strontium aluminate via sputtering deposition for freestanding oxide membranes

Evgenios Stylianidis, Marie Dallocchio, Bernat Mundet et al. (+6 more)

We report the epitaxial growth of high-quality water-soluble strontium aluminate films via sputtering deposition. We systematically investigate the dependence of the films structural quality on the growth conditions and we show that we can selectively grow, using the same target, both the cubic Sr3Al2O6 and the tetragonal Sr4Al2O7 phases by varying the atmosphere during growth. Using these water-soluble sacrificial layers we then synthesize ferromagnetic freestanding Sm2NiMnO6 membranes. By means of X-ray diffraction, synchrotron spectroscopic techniques and SQUID magnetometry, we demonstrate that our freestanding films exhibit properties comparable to epitaxial films.
Read the full abstract

All authors Evgenios Stylianidis, Marie Dallocchio, Bernat Mundet, Lucia Varbaro, Clementine Thibault, Christo Guguschev, Mario Brützam, Javier Herrero, Marta Gibert

Materials Science

Site-Selective Yttrium Substitution in Ti3AlC2 Enables Interlayer Engineering and Li Transport in Ti3C2Tx cathodes for High-Power Energy Storage

Tetiana Boichuk, Andrii Boichuk, Mahesh Eledath Changarath et al. (+5 more)

In this work, we introduce a precursor-level strategy by substitutionally doping the Ti3AlC2 MAX precursor with a small amount of Yttrium during top-down MAX preparation. This allows permanent structural changes that are retained in the resulting Ti3C2Tx MXene. Density functional theory (DFT) calculations identify the outer Ti(4f) site, facing the Al layer, as the preferred incorporation site for Y under the Al-excess synthesis conditions used here, rather than the inner Ti(2a) or Al(2b) sites. This site-specific substitution is consistent with the experimentally observed lattice expansion and carbide-like Y bonding and provides a microscopic basis for the structural changes retained in the resulting Ti3C2Tx MXene. Y incorporation expands the MXene interlayer spacing due to an increase in the amount of hydroxyl surface terminations, creating more favorable pathways for lithium-ion transport. Comprehensive structural characterization (including XRD, XPS and TEM) confirms these modifications. As a result, the Y-doped Ti3C2Tx cathode shows diffusion-controlled charge storage with a Li diffusion coefficient of 10-9-10-11 cm2/s. It delivers a reversible capacity of about 130 mAh/g at 0.2 C and retains 74 mAh/g after 1000 cycles at 2 C with nearly 100% Coulombic efficiency. The electrode also achieves a high power density of up to 3970 W/kg, outperforming the undoped MXene and previously reported multilayered MXene cathodes. These results show that substitutional doping of the MAX precursor is a promising strategy for controlling the interlayer structure of MXenes and improving ion transport, providing a new route for the development of high-power energy-storage electrodes.
Read the full abstract

All authors Tetiana Boichuk, Andrii Boichuk, Mahesh Eledath Changarath, Joao Fonseca, Said Agouram, Marie Finas, Alejandro Molina-Sanchez, Juan F. Sanchez-Royo

Materials Science

Electro-Thermal Origins of Enhanced Performance and Scalability in Disc-Type Phase-Change Memory

Ghazi Sarwat Syed, Loris Coccia, Siddharth Gautam et al. (+2 more)

Disc-type phase-change memory is a promising device architecture for analog in-memory computing, enabled by the unique physical properties of ultra-thin phase-change materials and the device geometry. In this study, we develop a comparative analytical framework using compact electro-thermal models to examine the state dependent readout and programming behavior of these devices. The framework provides insight into the fundamental physical mechanisms responsible for their enhanced functionality and highlights promising directions for further device optimization and performance improvement.
Read the full abstract

All authors Ghazi Sarwat Syed, Loris Coccia, Siddharth Gautam, Vara Prasad Jonnalagadda, Abu Sebastian