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Physics Condensed Matter Materials Science

cond-mat.mtrl-sci Watch Materials Science

Wednesday 10 June

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

Nonlinear Mechanics and Predictable Bifurcation of Multi-Cell Kresling Origami Chains

Songlin Yue, Leo de Waal, David Garcia Cava et al. (+1 more)

Meta-structures that display axial-twist coupling can be achieved through the emerging kinematics in Kresling origami patterns. A central challenge in these structures is understanding their nonlinear mechanical behaviour, specifically their equilibrium branches and bifurcation diagrams. This involves identifying relationships between desired responses and the geometric variables that define the design space, including the Kresling polygon count, initial twist angle, height, radius, and crease lengths. As the number of constituent units increases in an n-layer chain, we track complex equilibrium branches extending into the post-critical regime under successive instabilities, including branch-point bifurcations and limit-point instabilities. This work begins by establishing the relationship between the geometric design variables and the response curves of the assembled chain by modelling the crease lines as axial-load-carrying elements. Subsequently, equilibrium branches and instabilities are systematically investigated via continuation and bifurcation analysis, beginning with the single-layer system and progressively extending to two- and three-layer configurations. Finally, a generalisation strategy is proposed to extend these findings to an n-layer Kresling chain. This strategy enables the predictive construction of equilibrium paths and the inverse design of multi-layer meta-structures, using prescribed critical points to control post-critical behaviour. It provides a foundation for the inverse design and optimisation of architected mechanical metamaterials with programmable responses.
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All authors Songlin Yue, Leo de Waal, David Garcia Cava, Marcelo A. Dias

Materials Science

Bulk-like Compressibility of the Au-Au Metallic Bond in the Atomically Precise $\mathrm{Au}_{25}$ Cluster

Camino Martín-Sánchez, Khadijetou Ahmed Ethmane, Nicholas Giamboni et al. (+3 more)

We present a high-pressure single-crystal X-ray diffraction study of the atomically precise $\mathrm{Au}_{25}(\mathrm{PET})_{18}^{q}$ cluster ($q=-1,0$) up to 10 GPa under strictly hydrostatic conditions. Our crystallographic analysis provides direct evidence for the pressure-induced phase transitions previously suggested by spectroscopic studies. Structural refinements reveal that the cluster accommodates compression through the reorganization of the flexible ligand shell and secondary distortions of the staple motifs, while the $\mathrm{Au}_{13}$ icosahedral core remains intact. Notably, the internal Au-Au distances exhibit a monotonic contraction that quantitatively mirrors the compressibility of bulk gold. This invariant rigidity at the sub-nanometer scale demonstrates that the fundamental stiffness of the metallic bond is preserved regardless of size. Our findings reconcile previous contradictions in the elasticity of metal nanostructures by isolating the intrinsic mechanical response of the gold kernel from extrinsic structural and experimental artifacts.
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All authors Camino Martín-Sánchez, Khadijetou Ahmed Ethmane, Nicholas Giamboni, Latévi Max Lawson Daku, Céline Besnard, Thomas Bürgi

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

Spin-Orbit Torque and Magnetization Switching in 2D Ferromagnetic Devices

Bao-Huei Huang, Hong Guo and Yu-Hui Tang

Current-induced spin-orbit torque has emerged as a powerful technique for manipulating magnetization switching of ferromagnet/nonmagnet (FM/NM) based memory cell. By investigating nonequilibrium spin torque effect in a van der Waals heterobilayer, trigonal $\text{Cr}_{3}\text{Te}_{4}/\text{PtTe}_{2}$, the first-principles quantum transport calculations are applied to determine both local spin induction, resulting from Rashba-Edelstein effect in the FM layer, and spin current injection, flowing from the NM to the FM layer. Our work reveals that local spin induction significantly generates the fieldlike torque, which primarily governs the switching current in systems with strong in-plane magnetic anisotropy. Our work emphasizes the importance of optimizing spin Hall effect in the NM layer for perpendicular magnetic anisotropy (PMA)-based magnetization switching and maximizing the Rashba effect in the FM layer for in-plane magnetic anisotropy (IMA)-based switching.
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Materials Science · Cross-listed from cond-mat.supr-con

Ambient and Pressure Dependent Superconductivity with Hydrogen Storage Potential in Quaternary Hydride LiMgZr2H12: A Comprehensive First-principles Insights

Jubair Hossan Abir, Tauhidur Rahman, Salauddin Muhammad Anis et al. (+2 more)

Molecular hydrides have attracted relatively less attention in the search for high Tc superconductors because their hydrogen quasi-molecular units tend to be electronically inactive for superconductivity. In contrast, hydrogen rich compounds under high pressure have been widely considered strong candidates for achieving room-temperature superconductivity. However, their dependence on extreme pressure conditions significantly constrains their practical applicability. This work investigates hydrogen-rich superconducting materials that may be stable under ambient pressure conditions. Motivated by recent studies on the MgZrH2n family, a LiMgZr2H12 structure with Pmmm symmetry was designed. The mechanical, thermodynamic, and dynamical stability of the compound, together with its electronic and optical properties, were systematically investigated using first-principles calculations. Li doping in LiMgZr2H12 significantly increases the hydrogen derived contribution near the Fermi level (EF) and strengthens the electron-phonon coupling constant ({\lambda}) compared with MgZrH6. LiMgZr2H12 exhibits a critical temperature of 72.76 K at ambient pressure, which is further enhanced by applying pressure. At 10 GPa the critical temperature increases to 77.3 K. Elastic property analysis shows that the material remains mechanically stable over the pressure range studied (0-10 GPa). It also behaves like a ductile material suitable for current carrying applications. The material has a high machinability index, which is much higher than that of stainless steels. In addition, LiMgZr2H12 exhibits a gravimetric hydrogen storage capacity of 5.36 wt%, indicating its potential as a promising candidate for hybrid hydrogen storage technologies. This work offers a new direction for designing high-Tc hydrides at ambient conditions.
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All authors Jubair Hossan Abir, Tauhidur Rahman, Salauddin Muhammad Anis, Saleh Hasan Naqib, Raihana Shams Islam

Materials Science

Integrated magnonic neural circuits based on nonlinear wave neurons

Mengying Guo, Xudong Jing, Kristýna Davidkova et al. (+11 more)

Artificial intelligence is driving intense interest in alternative computing hardware capable of neural information processing beyond conventional charge-based electronics. Among emerging approaches, wave-based computing promises highly parallel and energy-efficient operation, but scalable physical neural hardware has remained elusive because wave systems generally lack cascadable nonlinear neurons with signal regeneration and phase-robust operation. Here we demonstrate integrated magnonic neural circuits based on nonlinear threshold neurons realized in nanoscale yttrium iron garnet waveguides. The neurons perform weighted summation of multiple spin-wave inputs, while a pump-controlled nonlinear activation defines continuously tunable firing thresholds. Owing to deeply nonlinear spin-wave dynamics, the activated neurons emit self-normalized outputs whose intensities are largely independent of the input amplitudes, while nonlinear phase self-adjustment suppresses sensitivity to the relative input phases, enabling deterministic neuron-to-neuron cascading without external signal restoration. We experimentally realize programmable threshold neurons, reconfigurable weighted classification and deterministic cascading between sequential neuronal stages, and further demonstrate reconfigurable physical pattern recognition in a seven-neuron integrated magnonic circuit through experimental classification of the binary letter patterns 'HUST'. These results establish nonlinear magnons as a scalable platform for integrated neural hardware and position nonlinear wave dynamics as a general paradigm for physical neuromorphic computing.
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All authors Mengying Guo, Xudong Jing, Kristýna Davidkova, Roman Verba, Zhenyu Zhou, Xueyu Guo, Carsten Dubs, Chuan Gao, Yiheng Rao, Kaiming Cai, Jing Li, Philipp Pirro, Andrii V. Chumak, Qi Wang

Materials Science

Observation of coherently modulated thermal phonon band and lifetime in superlattice

Yuxuan Liao, Hiroshi Uchiyama, Naomi Nagai et al. (+12 more)

Manipulating phonon band structures through wave interference in artificial periodic nanostructures is of fundamental interest and forms the foundation of phonon band engineering. Yet, direct observation of thermal phonon wave interference has remained elusive despite half a century of extensive research. Here, utilizing inelastic x-ray scattering, we directly observed momentum-resolved coherently modulated thermal phonon bands and lifetimes in a short-period GaAs/AlAs superlattice at 300 K. The modulation persists at even 500 K, demonstrating robust coherent thermal phonon transport at high temperatures. Our measurements, combined with ab initio lattice-dynamics calculations, further show that thermal phonon interference expands the three-phonon scattering phase space and strengthens anharmonic effects, highlighting the interplay between phonon band modulation and anharmonicity. Our observations establish nanostructuring as a versatile route for engineering thermal phonon bands and lifetimes at high temperatures across diverse applications.
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All authors Yuxuan Liao, Hiroshi Uchiyama, Naomi Nagai, Natalia Morais, Taiushun Manjo, Rulei Guo, Harsh Chandra, Ryohei Nagahiro, Bin Xu, Hiroshi Fukui, Daisuke Ishikawa, Alfred Q.R. Baron, Yasuhiko Arakawa, Kazuhiko Hirakawa, Junichiro Shiomi

Materials Science

Unveiling Orbital-mediated Ultrafast Demagnetization in Rare Earth-Transition-Metal Ferrimagnets

Jianwen Gao, Linlin Zhang, Mingli Ge et al. (+12 more)

The ultimate speed limit of magnetic recording and spintronic devices is set by the efficiency of angular-momentum transfer during ultrafast demagnetization, yet its microscopic pathway in Rare-Earth-Transition-Metal (RE-TM) ferrimagnets remains debated. Here, we establish an orbital-mediated framework in which 3d spin-orbit coupling (SOC) governs angular momentum (AM) dissipation. Strong 3d-SOC in RE-Co enables sub-picosecond, single-step demagnetization via direct orbital-to-lattice transfer, whereas weak 3d-SOC in RE-Fe redirects AM into 4f orbitals, producing slower two-step dynamics. The second-stage rate scales with 4f-SOC strength, revealing a distinct orbital-mediated dissipation channel. Using time-resolved magneto-optical Kerr measurements, supported by an extended four-temperature model, corroborate this picture across diverse RE-TM systems (RE = Sm, Gd, Tb, Dy, Ho and TM = Fe, Co, CoNi). Our results identify the SOC-driven competition between 3d and 4f orbital channels as the universal mechanism governing ultrafast demagnetization in RE-TM ferrimagnets, enabling rational design of the switching speed for next-generation spintronic devices.
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All authors Jianwen Gao, Linlin Zhang, Mingli Ge, Runhua Zhang, Jinshan Wang, Hui Li, Xiaowei Zhou, Zhu Liu, Zongzhi Zhang, Li Xi, Yalu Zuo, Chenglong Jia, Feng Qiu, Shaojie Hu, Yang Ren

Materials Science

Chiral Magnons and Cycloidal Phonons in Altermagnetic CuF$_{2}$ Monolayer

Andrea M. León, Matías F. Torreblanca, Carmine Autieri et al. (+1 more)

Altermagnetism establishes momentum-dependent spin splitting through non-symmorphic crystal symmetries, yet whether these same symmetries simultaneously govern spin and lattice collective excitations remains open. Here we show, using first-principles calculations and linear spin-wave theory, that monolayer CuF$_2$ hosts both chirality-split magnons and cycloidal phonons controlled by the same $P2_1/c$ symmetry operations. The altermagnetic order drives strongly anisotropic magnon chirality via symmetric anisotropic exchange, with Dzyaloshinskii–Moriya interactions acting as a weak secondary modulation. Crucially, the phonon and magnon chiral responses are directionally complementary: cycloidal phonon angular momentum emerges precisely where magnon chirality is symmetry-suppressed, and vice versa. The magnon bands further carry quantized Chern numbers $C^M = \pm 2$, confirming non-trivial altermagnetic topology. These results establish monolayer CuF$_2$ as a platform where a single symmetry framework engineers magnonic, phononic, and topological responses, providing a direct connection between altermagnetism and spin-lattice chirality in two-dimensional materials.
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All authors Andrea M. León, Matías F. Torreblanca, Carmine Autieri, Jhon W. González

Materials Science · Cross-listed from cs.LG

Range-Aware Bayesian Optimization for Discovering Diverse Designs within Target Property Windows

Shengli Jiang, Jason Wu, Charles M. Schroeder et al. (+1 more)

In many materials and product design problems, desirable candidates exhibit properties that fall within an acceptable range rather than achieve a single optimum. Recovering multiple, distinct solutions that satisfy such specifications is also practically valuable, as some candidates may be preferred for reasons of cost, processability, or robustness that are difficult to encode directly in an objective function. Here, we develop a range-aware Bayesian optimization (BO) framework in which the acquisition function directly scores the posterior probability that a candidate satisfies a target range. The framework naturally extends to parallel pursuit of multiple distinct specifications over a shared candidate space. Across benchmark tasks, range-aware acquisition consistently recovers larger and more diverse sets of valid designs than standard BO baselines and recent goal-seeking methods. Its utility is further demonstrated in two practically motivated design case studies involving optimizing reaction conditions for polymer synthesis and sequence-defined oligomer discovery for prescribed optical absorption bands, supported by quantum chemical calculations. These results suggest that range-aware BO can provide a practical and sample-efficient foundation for specification-driven design, particularly when design flexibility and solution diversity are important considerations.
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All authors Shengli Jiang, Jason Wu, Charles M. Schroeder, Michael A. Webb

Tuesday 9 June

Materials Science

Nucleation instability preempts relativistic domain wall transport in high-exchange ferrimagnetic nanowires

Pietro Diona

Current-driven domain wall motion in ferrimagnets can approach the spin-wave velocity, giving rise to relativistic-like dynamics. While this regime has been experimentally observed in crystalline ferrimagnetic garnets and amorphous GdFeCo, the material conditions that determine whether it can be accessed remain unresolved. Here, we investigate spin-orbit-torque-driven domain wall motion in high-exchange GdCo nanowires using magneto-optical Kerr effect microscopy. We find that nucleation preempts relativistic transport. In GdCo, no velocity saturation or high-field collapse is observed. Instead, the large exchange interaction raises the maximum spin-wave group velocity to $\approx 7\text{--}9~\mathrm{km/s}$, far above the experimentally accessible domain wall velocities. Before this limit can be approached, increasing current density and in-plane magnetic field induce domain nucleation, disrupting steady-state propagation. We map the boundary separating domain wall transport from nucleation instability and show that the nucleation threshold decreases with pulse duration, consistent with thermally assisted barrier crossing. These results identify nucleation as the mechanism that prevents access to the relativistic regime in high-exchange ferrimagnets and establish a dynamical phase boundary between steady propagation and nucleation.
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Materials Science · Cross-listed from quant-ph

A Cryogenic Uniaxial Strain Cell for Quantum Devices

Bradley Lloyd, Davis Rash, Chandler Wilburn et al. (+2 more)

Mechanical strain is a powerful resource for tuning quantum systems, but existing piezoelectric strain cells are generally optimized for fragile, high-aspect-ratio single crystals rather than the thick, square-profile chips typical of semiconductor quantum devices. Furthermore, adapting these cells for qubits requires accommodating dense RF and DC wiring while maintaining strict electrical isolation from high-voltage piezo actuators. Here, we present a piezoelectric uniaxial strain cell designed to homogeneously strain thick, square-profile substrates. We introduce a highly symmetric dual-chip loading configuration that effectively suppresses flexural deformation and shear stress. The cell integrates a high-density RF/DC interposer to support standard wire bonding and encloses the actuators in a grounded Faraday cage to prevent unwanted Stark shifts in the device layer. Finite element simulations confirm that combining stiff actuators with this symmetric mounting drastically improves strain homogeneity. Finally, we validate the apparatus experimentally by applying uniaxial strain to a 200 $\mu$m thick silicon die. Surface strain measurements demonstrate an applied strain of 215 $\mu\epsilon$ for 200 V applied piezo bias.
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All authors Bradley Lloyd, Davis Rash, Chandler Wilburn, Paul Kliewer, Meenakshi Singh

Materials Science

Screening of the Coulomb interaction in Carbon Nanotubes: A First-Principles cRPA study

Mohadese Rezayi and Hanif Hadipour

We investigate the electronic screening of long-range Coulomb interactions in carbon nanotubes with different chiralities using first-principles calculations within the random-phase approximation. Depending on their wrapping vector, carbon nanotubes exhibit either metallic or semiconducting behavior, providing an ideal platform to explore how reduced dimensionality and electronic structure govern screening in one-dimensional systems. The strength of on-site Coulomb interactions in these compounds falls within the range of 3.5 to 5 eV, which is approximately 2-3 eV smaller than the corresponding values in nanoribbon compounds. This reduction subsequently affects the value of long-range interactions, consistent with experimental results regarding the smaller binding energy of excitons in nanotubes. Despite their common carbon backbone, we find that the effective interaction landscape depends not only on metallicity but also sensitively on chirality and band topology. In particular, armchair and zigzag nanotubes with similar electronic character exhibit markedly different screening efficiencies. Our results establish a unified microscopic picture of electronic screening in carbon nanotubes and place them in direct context with previous first-principles studies of low-dimensional carbon nanostructures.
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Materials Science

Topological Phase Transition in Mechanical Honeycomb Lattice

Yi Chen, Xiaoning Liu and Gengkai Hu

Topological materials provide a new tool to direct wave energy with unprecedented precision and robustness. Three elastic topological phases, the valley Hall, Chern and spin Hall insulators, are currently studied, and they are achieved separately in rather distinct configurations. Here, we explore analytically various topological phase transitions for in-plane elastic wave in a unified mass-spring honeycomb lattice. It is demonstrated that the three elastic topological phases can be realized in this single lattice by designing mass, stiffness or introducing Coriolis' effect. In particular, the interface between valley Hall and Chern insulators is found to support topological interface mode for the first time. Perturbation method is used to derive the analytic effective continuum model in the neighbor of band degeneracy, and the physics in topological phase transitions are revealed through evaluation of topological invariants. The topologically protected interface states, their decaying profile as well as the pseudo-spin-indicating polarization specific for elastic wave are systematically analyzed, and these results are further confirmed numerically by Bloch wave analysis of domain wall strip and transient simulation of finite sized sample. This study offers a concise and unified analytical model to explore topology nature of elastic wave, and can provide intuitive guidance to design of continuum mechanical topological materials.
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Materials Science

Defect Tolerance in Trigonal Selenium Photovoltaics

Jiban Kangsabanik, Kasper Tolborg, Thomas Olsen et al. (+1 more)

Understanding how point defects fundamentally influence photovoltaic performance remains a central question for emerging wide-band gap absorbers. Trigonal selenium (t-Se) has recently re-emerged as a promising photovoltaic material due to its near-optimal band gap for tandem and indoor applications. Here we quantify defect-assisted Shockley-Read-Hall (SRH) recombination in t-Se using first principles calculations across a large and chemically diverse set of point defects. Our results suggest that t-Se is intrinsically defect tolerant. Despite the presence of multiple deep levels in the gap, recombination via nonradiative multi-phonon emission processes is strongly suppressed by large lattice reorganizations and large energy releases of at least 0.5 EG per recombination event, while radiative defect-assisted capture also remains too small to account for the observed device losses. Consequently, SRH recombination mediated by realistic concentrations of point defects cannot account for the observed efficiency limitations in selenium photovoltaics. We explore trends in both radiative and nonradiative SRH recombination rates across the defect data set, highlighting their complex dependence on defect level position, lattice relaxation, charge state, and doping conditions. These findings establish trigonal selenium as a defect-tolerant wide-band-gap absorber and provide transferable design principles for optimizing next-generation photovoltaic materials for tandem and indoor applications.
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All authors Jiban Kangsabanik, Kasper Tolborg, Thomas Olsen, Kristian S. Thygesen

Materials Science · Cross-listed from physics.optics

Pulse-Duration Scaling of Ultrafast Laser-Induced Damage Threshold in Hybrid Gratings

Ziyao Su and Enam Chowdhury

High damage threshold gratings are in demand worldwide as critical components for next generation ultrahigh intensity lasers. Here we investigate the pulse-duration dependence of ultrafast laser-induced damage thresholds (LIDT) in hybrid multilayer dielectric gratings, touted to combine superior performance properties of both metallic and multilayer dielectric (MLD) gratings, using a dynamic finite-difference time-domain model incorporated with linear and non-linear absorption models. Simulations agree with reported experimental LIDT values for three representative designs and predict scaling exponents which vary with pulse durations ranging from 10 to 500 fs. The results reveal strong dependence on both material bandgap and grating field distribution, providing guidance for designing high LIDT gratings.
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Materials Science

Reconfigurable Strain Gradient Polarity in Crystalline Oxide Nanomembranes for Controlled Bending of Functional Materials

Tiffany C. Wang, Minyong Han, Varun Harbola et al. (+1 more)

We report the fabrication and mechanical characterization of a "bubble" geometry for accessing local strain gradients using freestanding, single-crystalline manganite nanomembranes: a switchable bistable nanodrum, with opposite strain gradient polarities. By leveraging epitaxial strain as a source of pre-strain and with control of geometrical and mechanical boundary conditions, the fabricated device can support strain gradients with strain variation ranging from 0.01% to 1%. Switching energetics can be designed to configure the bubble morphology. By providing a mechanical framework for sustained strain gradients, this platform supports scalable oxide membrane applications such as the mechanical manipulation of magnetism, coupled to local probes.
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All authors Tiffany C. Wang, Minyong Han, Varun Harbola, Harold Y. Hwang

Materials Science

Roughness-robust surface altermagnetism in $PT$ antiferromagnets

K. D. Belashchenko

Surface altermagnetism extends spin splitting beyond bulk altermagnets through symmetry reduction at surfaces and interfaces. An existing classification applies to the local symmetry of atomically flat surface terraces. The present paper addresses the symmetry of macroscopic spin-momentum correlations that survive averaging over compensated rough surfaces. These correlations are governed by the surface antisymmetry Laue point group. Rough-surface altermagnetism is forbidden at any surface of a magnet whose antisymmetry space group contains antitranslations, and the classification therefore reduces to $PT$-symmetric antiferromagnets. By restoring all symmetries leaving the surface normal invariant, roughness can generate compensated surface altermagnets from uncompensated flat terminations, increase the surface symmetry, or suppress spin splitting. By combining bulk switchability with altermagnetic surface transport properties, roughness-robust surface altermagnetism in $PT$-symmetric antiferromagnets provides a route toward spintronic functionality.
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Materials Science

Flower-like WO3-modified Vulcan carbon GDEs for photoelectro-Fenton process: Efficient ciprofloxacin degradation and mechanistic insights

João Paulo C. Moura, Vanessa S. Antonin, Caio Machado Fernandes et al. (+8 more)

Electrochemical H2O2 synthesis was investigated using a 3 percent WO3 C gas diffusion electrode GDE. The catalyst outperformed bare Vulcan carbon, generating H2O2 concentrations of 423, 586, and 916 mg L at 50, 75, and 100 mA cm2, respectively, maintaining around 70 percent current efficiency. This performance and lower energy consumption are attributed to the WO3 carbon synergistic effect. In electro Fenton EF applications, the WO3 C GDE achieved rapid initial ciprofloxacin CIP degradation of around 70 percent in 30 min, though limited later by slow Fe2 regeneration. Incorporating UV light photoelectro Fenton overcame this constraint, yielding complete CIP removal within 90 min, while a boron doped diamond BDD anode enhanced total organic carbon TOC mineralization to 66 percent. The proposed degradation mechanism proceeds via hydroxyl radical attack on the piperazine ring with or without defluorination and quinolone ring oxidation, with theoretical analysis confirming reduced environmental toxicity of the transformation products. Overall, WO3 C GDEs represent a highly efficient strategy for H2O2 generation and wastewater remediation.
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All authors João Paulo C. Moura, Vanessa S. Antonin, Caio Machado Fernandes, Aline B. Trench, Erica S. Conrado, Michell O. Almeida, Kathia M. Honorio, Renata Colombo, Rafael Sotana, Ana M.P. Neto, Mauro C. Santos

Materials Science

Approaching the Limit of Intrinsic Crystalline Thermal Insulation

Ruihuan Cheng, Zhiqiang Cui, Mani Jayaraman et al. (+9 more)

Crystalline materials with ultralow thermal conductivity ($\kappa$) are potential thermal barrier coatings or thermoelectrics, yet the discovery of ultralow-$\kappa$ materials remains inefficient due to the limitations of trial-and-error approaches. Herein, we propose a state-of-the-art high-throughput workflow that integrates universal machine learning interatomic potentials with high-fidelity phonon transport theories to accelerate the exploration of thermal insulators. Applying this approach, we identify dozens of crystalline materials with intrinsic room-temperature $\kappa$ values below 0.2 $\rm W m^{-1} K^{-1}$. Among them, we report and experimentally validate CsTlI$_4$, a record-breaking material with an ultralow $\kappa$ of 0.14 $\rm W m^{-1} K^{-1}$ at 300 K. Structural and bond analyses reveal that a hierarchical bonding framework, consisting of multi-coordinated Cs-I and antibonding Tl-I interactions, leads to weak chemical bonding and a soft lattice. These features reduce phonon group velocities, enhance phonon scattering, and induce strong vibrational mismatch between sublattices, collectively suppressing both particle-like phonon propagation and wave-like tunneling. Beyond this specific system, we establish physically interpretable descriptors based on interatomic force constants that correlate strongly with ultralow $\kappa$ and capture the role of bonding hierarchy and coordination environments in governing thermal transport. This work demonstrates a robust data-driven strategy for accelerating the discovery of thermal insulators and provides microscopic insight into how hierarchical bonding and strong anharmonicity cooperate to impede heat-carrying vibrations.
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All authors Ruihuan Cheng, Zhiqiang Cui, Mani Jayaraman, Lincong Ji, Chen Wang, Zesheng Zeng, Petr Levinsky, Jiri Hejtmanek, Christophe Candolfi, Emmanuel Guilmeau, Xingchen Shen, Yue Chen

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

The UZH protocol: Separating errors and constructing improved CP2K basis sets and pseudopotentials

Hossein Mirhosseini, Tiziano M. A. Müller, Matthias Krack et al. (+2 more)

Reliable density-functional simulations require numerical settings whose residual errors are smaller than the chemical and materials trends being interpreted. In CP2K/Quickstep, this requirement is complicated by the joint use of atom-centered Gaussian basis sets and norm-conserving pseudopotentials: a code-to-code discrepancy usually contains both contributions. We present the UZH protocol, a closed-loop CP2K workflow that calibrates molecularly optimized Gaussian basis sets on small molecules, validates the resulting settings in unary-crystal equation-of-state benchmarks, identifies whether the limiting approximation is the Gaussian basis or the pseudopotential. The diagnosis is then used to revise the parameter files. The central diagnostic is a three-way comparison between production CP2K-GTH-UZH calculations, SIRIUS calculations using the same Goedecker–Teter–Hutter pseudopotential in a systematic plane-wave representation, and all-electron full-potential linearized augmented-plane-wave SIRIUS references. This construction decomposes the practical CP2K error into a Gaussian-basis component and a pseudopotential component. The protocol distinguishes basis-limited noble-gas and heavy-element cases from pseudopotential-limited transition-metal cases, guides targeted revisions with the CP2K basis and pseudopotential optimizers, and produces improved MOLOPT basis sets and GTH pseudopotentials as explicit outputs of the workflow. The UZH protocol is therefore constructive: it does not merely measure or reduce errors a posteriori, but allows turning verification outliers into validated CP2K parameter files for simulations across molecules and condensed phases.
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All authors Hossein Mirhosseini, Tiziano M. A. Müller, Matthias Krack, Thomas D. Kühne, Jürg Hutter

Materials Science

In-situ total scattering investigation of crystalline ordering in amorphous ion-beam sputtered thin films for interferometric gravitational wave detectors

Alberto Martinelli, Giulio Favaro, Giacomo Ciani et al. (+9 more)

Amorphous tantala is an important optical material used in a number of high-precision optical applications, including gravitational wave interferometry. In this paper, we study in-situ the structural changes that occur in amorphous ion-beam sputtered coatings during an annealing treatment by means of a synchrotron radiation scattering experiment. The scattering signal is measured as a function of time on a large range of the Q-space. X-Ray diffraction and Rietveld analysis are used to study crystallization during the annealing treatment, whereas pair distribution function analysis allows to inspect the structural changes occurring during the amorphous to crystalline transition. Our findings indicate that several structural rearrangements occur in parallel, namely a first quick establishment of a backbone structure in the cationic substructure appearing on a rather extended range (up to 100 Angstrom), followed by a progressive rearrangement of the oxygen atoms environment which gradually increases the crystallinity of the structure.
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All authors Alberto Martinelli, Giulio Favaro, Giacomo Ciani, Livia Conti, Jean-Pierre Zendri, David Hofman, Massimo Granata, Angela Trapananti, Flavio Travasso, Laura Silenzi, Valeria Milotti, Marco Bazzan

Materials Science

Synthetic pre-training of graph-network models for predicting solid-state NMR parameters

Chiheb Ben Mahmoud, Carlos Bornes, Christopher J. Heard et al. (+3 more)

Nuclear magnetic resonance (NMR) is a powerful probe of atomic structure, but accurate quantum-mechanical predictions of tensorial NMR parameters are computationally demanding. This creates a bottleneck both for direct quantum-mechanical studies and for collecting high-quality training data for machine-learning (ML) models. Here, we introduce a synthetic pre-training and fine-tuning protocol for graph-based ML models of solid-state NMR parameters. We first pre-train models on synthetic tensorial data, as obtained using an existing ML model, and subsequently fine-tune those models on new ground-truth data. We observe a pronounced improvement in data efficiency when pre-training and fine-tuning span the same compositional and configurational space, and we carry out initial experiments regarding chemical transferability. Our work outlines a route toward future data-efficient training workflows for tensorial ML models for solid-state NMR, combining inexpensive synthetic supervision with targeted first-principles refinement.
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All authors Chiheb Ben Mahmoud, Carlos Bornes, Christopher J. Heard, Lukáš Grajciar, Jonathan R. Yates, Volker L. Deringer

Materials Science

Influence of CeO$_2$MnO$_x$ heterostructure on Hydrogen Peroxide Electrogeneration on Carbon-Based Catalysts

Caroline de O. Carrilho, Juliana M. S. de Jesus, João Paulo C. Moura et al. (+7 more)

The sustainable electrogeneration of hydrogen peroxide (H2O2) via the two-electron oxygen reduction reaction (2e$^-$ ORR) represents a promising alternative to conventional production methods. In this study, CeO2 and CeO2MnOx nanoparticles were synthesized and supported on Vulcan XC-72 carbon at varying loadings (1, 3, and 5%), aiming to assess the lowest metal loading and high H2O2 electrosynthesis. Physicochemical characterizations confirmed the successful formation of CeO2 nanowires and the effectiveness of the MnOx surface modification. XRD, TEM, XPS, EPR, and contact angle analyses revealed that CeO2 loading increased surface hydrophilicity through the presence of oxygenated functional groups, thereby favoring electrochemical activity. On the other hand, all CeO2MnOx loadings were statistically equivalent to Vulcan XC-72 in terms of contact angle. Electrochemical evaluations using a rotating ring-disk electrode (RRDE) demonstrated enhanced ORR activity and high H2O2 selectivity for the 1% CeO2MnOx/C and 3% CeO2/C catalysts, achieving up to 90% selectivity and elevated ring currents. The results suggest that low metal loading and surface modification via MnOx improve the balance between active site exposure, oxygen adsorption, and intermediate stabilization, thus favoring the selective 2e$^-$ pathway. These findings support the development of cost-effective, non-noble-metal catalysts for green H2O2 production via electrosynthesis.
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All authors Caroline de O. Carrilho, Juliana M. S. de Jesus, João Paulo C. Moura, Dara Silva Santos, Aline B. Trench, Caio Machado Fernandes, Aila O. Santos, Odivaldo C. Alves, Júlio C. M. Silva, Mauro C. dos Santos

Materials Science

Direction-Dependent Quantum Transport Properties of MoS$_2$ Integrated into Biphenylene Configuration

Gözde Özbal Sarg{\i}n

Motivated by the experimental realization of the two-dimensional (2D) carbon biphenylene network (BPN), the theoretical extension of the BPN topology to various groups of elements was successfully implemented. In this work, we conducted first principles and quantum transport calculations to reveal the electronic, thermal, thermoelectric performance and current-voltage (I-V) behavior of the pristine MoS$_2$-BPN by using density functional theory (DFT) combined with Non-Equilibrium Green's Function (NEGF) formalism. At room temperature, the phonon thermal conductance is remarkably low along both the armchair and zigzag orientations, with values of 0.28 nW/K and 0.23 nW/K, respectively. The directional dependence of the electronic and thermal transport properties is clearly reflected in the thermoelectric figure of merit ($zT$) values, which reach first peaks at 0.27 and 0.19 along the armchair and zigzag directions, respectively. The current-voltage ($I-V$) characteristics demonstrate an exceptionally strong transport anisotropy, characterized by a substantial current ratio of $I_{\text{armchair}}/I_{\text{zigzag}} \approx 7 \times 10^4$. Furthermore, while the current along the armchair direction increases steadily with the applied bias, transport along the zigzag direction is characterized by a pronounced intrinsic negative differential conductance (NDC). This contrast highlights fundamentally distinct charge transport mechanisms along the two orthogonal axes. Consequently, different directions of this BPN phase of MoS$_2$ can be tailored for distinct nanoelectronic applications, where the armchair and zigzag axes serve as a reliable current switch and an active NDC device, respectively.
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Materials Science

Ab initio study of magnetism in pristine and defective MnBi2Te4

Ana Beatriz Pedro Fontes, Jiaqi Zhou, Simon M.-M. Dubois et al. (+1 more)

The magnetic material MnBi2Te4 (MBT) has garnered significant attention due to its unique combination of long-range antiferromagnetism and nontrivial topological electronic properties. However, experimental measurements report inconsistent magnetizations, which could be attributed to a variety of intrinsic defects. To date, a comprehensive investigation of defect-engineered MBT systems has not yet been established. Employing state-of-the-art $ab~initio$ techniques, this work systematically investigates the influence of various experimentally reported defects on the magnetic properties of bulk and monolayer MBT at different concentrations. Mn-vacancy and Mn-rich defects are found to enhance the ferromagnetism of bulk MBT. The investigation of Mn-rich and intermixing defects in the monolayer reveals that subtle structural and electronic modifications can alter the magnetic coupling. Projection onto a Heisenberg Hamiltonian demonstrates that defects modify exchange interactions, thereby giving rise to distinct magnetic ground states. This work sheds light on magnetic coupling mechanisms and provides guidelines for the experimental control of magnetism in MnBi2Te4.
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All authors Ana Beatriz Pedro Fontes, Jiaqi Zhou, Simon M.-M. Dubois, Jean-Christophe Charlier

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

Field-Induced Up-Up-Down State and Frustrated Magnetism in a Non-Kramers Triangular Antiferromagnet

Zhaoyi Li, Qinchen Duan, Bo Wen et al. (+2 more)

A previously unreported triangular lattice (TL) antiferromagnet, TmZnGaO4, was synthesized as single crystals, and its crystal structure, magnetic susceptibilities, and specific heat were reported. Its crystal structure is isomorphic to that of the transverse-field Ising antiferromagnet TmMgGaO4, with Tm3+ ions located in the TLs, separated by a nonmagnetic bilayer composed mainly of Ga3+ and Zn2+ ions. The magnetic susceptibilities indicate the dominating antiferromagnetic interactions. The magnetization curves (M-H) exhibit strong easy-c-axis anisotropy, with a clear one-third magnetic plateau emerging, consistent with a field-induced up-up-down spin configuration. Instead of forming a conventional long-range magnetic order, the system exhibits two broad anomalies at 0.11 K and 2.81 K in zero-field specific heat measurements, highlighting the persistence of strong spin fluctuations and the potential for exotic quantum spin states. The above results reveal its future interest in exploring exotic quantum spin states in TmZnGaO4.
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All authors Zhaoyi Li, Qinchen Duan, Bo Wen, Ruidan Zhong, Shu Guo

Materials Science

Degeneracy and trajectory control of spin eigenmodes excited by fs-optical pulses in a nearly compensated ferrimagnet

G. Yu. Levkin, D. M. Krichevsky, N. A. Gusev et al. (+4 more)

We investigate optically excited spin dynamics in a uniaxial ferrimagnet near the magnetization compensation point under a magnetic field applied along the magnetic anisotropy axis. Experiment and numerical modeling reveal an unusual regime where the frequencies of two spin eigenmodes approach each other and become highly field sensitive. The modes, corresponding to opposite rotations of the Neel vector, simultaneously reverse their handedness at a critical field where their frequencies become degenerate. At this point, the two-frequency precessional dynamics collapses into a linear oscillations directed along the inverse-Faraday-effect excitation induced by a single pump pulse. We further show that a double-pulse excitation scheme enables control of the spin trajectory. These results uncover an unconventional dynamical regime in ferrimagnets and establish new opportunities for manipulating spin motion in magnonic systems and devices.
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All authors G. Yu. Levkin, D. M. Krichevsky, N. A. Gusev, A. K. Zvezdin, S. N. Polulyakh, V. I. Belotelov, D. O. Ignatyeva

Materials Science · Cross-listed from eess.IV

Low-Dose 3D Bonding Mapping Through "Soft" Core-Loss EELS Tomography and Unsupervised Deep Learning

Mario Pelaez-Fernandez, Daniel del-Pozo-Bueno, Adrien Teurtrie et al. (+10 more)

Resolving the 3D chemical configuration of beam-sensitive nanomaterials at high spatial resolution remains a persistent frontier in scanning transmission electron microscopy (STEM). The main limitation lies in the trade-off between high electron dose required for analytical signals and the large number of projections needed for tomographic reconstruction. Here, we achieve dose-efficient 3D bonding mapping of FeO/Fe$_3$O$_4$ core-shell nanocubes with high resolution via electron energy loss spectroscopy (EELS). Our approach relies on two developments. First, a standardless "soft" core-loss EELS methodology exploiting Fe-M$_{2,3}$ edges provides ${\sim}50\times$ higher dose efficiency than conventional Fe-L$_{2,3}$ edges, using the latter only as a source of FeO and Fe$_3$O$_4$ standards. Second, we introduce multi-channel deep image prior with total variation regularization (DIPm-TV), an unsupervised method for spectroscopic tomography that jointly reconstructs multiple channels by exploiting spatial correlations under sparse-view and low-dose conditions. Using simulated datasets, high-quality reconstructions are obtained from as few as nine projections over $-70^\circ$ to $+70^\circ$, without HAADF-STEM signal or symmetry constraints. Applied to FeO/Fe$_3$O$_4$ nanocubes, Fe-M$_{2,3}$ EELS maps show improved SNR and spatial resolution, revealing a thin outer FeO shell surrounding the magnetite shell. DIPm-TV yields ${\sim}1$ nm isotropic resolution oxidation-state volumes preserving cubic morphology, recovering the outer FeO shell, and revealing a small internal void, features not accessible with conventional reconstruction methods. This work establishes a pathway for low-dose 2D and 3D analytical mapping of beam-sensitive materials using shallow core-loss edges, enabling orders-of-magnitude dose reduction while maintaining spectral fidelity and reliable 3D information.
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All authors Mario Pelaez-Fernandez, Daniel del-Pozo-Bueno, Adrien Teurtrie, Serge Brosset, Maya Marinova, Phillipe Ciuciu, Marta Estrader, German Salazar-Alvarez, Francesca Peiró, Raul Arenal, Sonia Estradé, Zineb Saghi, Francisco De la Peña

Materials Science

Efficient analytic continuation approach to Bethe-Salpeter excitation spectra in selected energy windows

Ivan Duchemin and Xavier Blase

We explore the merits of building the Bethe-Salpeter absorption spectrum in a specific energy range using analytic continuation techniques. Specifically, we calculate iteratively a few $\bar{\bar \alpha}(z_k)$ polarizability tensors for a coarse set of $(z_k)$ frequencies in the complex-plane. These data allow constructing a continued-fraction representation for $\bar{\bar{\alpha}}(z)$ that is used to calculate the absorption spectrum close to the real energy axis in the desired energy range. The number and location of these sampling complex frequencies are discussed. The importance of building a continued-fraction representation of the full polarizability tensor with matrix-valued coefficients is emphasized. We show how to extract the poles of the continued fraction as a tool for analyzing the resulting spectra. We study as examples the valence excitations of a paradigmatic dipeptide, the C$_{60}$ fullerene and its PCBM derivative, together with the description of the surface plasmon resonance of the Ag$_{20}$ silver cluster. Further, the high-energy C$_{60}$ X-ray absorption spectrum is explored.
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Materials Science · Cross-listed from astro-ph.IM

UnReal-B : Real-Space DFT Solver for Matter in Extreme Magnetic Fields

Bhalchandra S. Pujari, Andrey Tokarev and Dipanjan Mitra

As new observational technologies reveal increasingly detailed properties of neutron star surfaces, the demand for accessible and extensible theoretical modeling tools continues to grow. We present UnReal-B, a real-space Density Functional Theory solver for one-dimensional chains of matter in extreme magnetic fields $B \approx 10^{12} - 10^{15},\mathrm{G}$. By employing the adiabatic approximation, UnReal-B, provides a streamlined numerical framework for calculating the electronic structure of strongly magnetized condensed matter. The solver is benchmarked against published results for several astrophysically relevant elements, demonstrating excellent agreement while maintaining a comparatively simple and transparent implementation. Released as open-source software, UnReal-B facilitates reproducible and community-driven investigations of neutron-star surface matter and provides a foundation for future developments motivated by emerging observational constraints.
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