Materials Science
Homogeneous Charge Relaxation in Organic Mixed Ionic-Electronic Conductors
Silan Zhang, Scott T. Keene, Junfu Tian et al. (+11 more)
Organic mixed ionic-electronic conductors (OMIECs) couple ionic and electronic signals, enabling energy storage, neuromorphic computing, and bioelectronics. However, how charge relaxes in water once the bias is removed, which determines how long stored states persist, remains unclear. Using operando charge photometry, we tracked charge in OMIEC films during biasing and open-
circuit relaxation. Under bias, charges moved as redox fronts. After bias removal, charge instead relaxed uniformly across the channel. Modeling and cryo-electron microscopy indicate that swelling creates connected water-rich pathways through the bulk. These pathways speed ion motion but also let stored charge leak away. Tuning the terminal side chain of a polythiophene controls water uptake and ion trapping. Bulky hydrophobic side chains enable stable programmable states, whereas hydrophilic side chains support fast electrophysiology sensing.
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All authors Silan Zhang, Scott T. Keene, Junfu Tian, Georgina E. Lindop, Simon M. Fairclough, Zhengkang Qu, Xian Wei Chua, Christopher Slaughter, Christina J. Kousseff, Caterina Ducati, Iain McCulloch, Henning Sirringhaus, Akshay Rao, George G. Malliaras
Materials Science
Comprehensive study of massively overlapping cascades in common elemental metals
Aslak Fellman, Jesper Byggmästar and Fredric Granberg
Massively overlapping cascades simulations were carried out in 21 elemental metals: Be, Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zr, Nb, Mo, Rh, Pd, Ag, Hf, Ta, W, Pt, Au and Pb. These elements have simple FCC, BCC and HCP
lattice structures. For each element, 2000 cumulative 5 keV cascades were simulated using molecular dynamics. The overlapping cascades were simulated using various classical analytical interatomic potentials as well as with machine-learning interatomic potentials for many of the elements. The general conclusion is that results from massively overlapping cascades simulations are very sensitive to the choice of interatomic potential across the periodic table. Furthermore, we see that FCC metals all form stacking fault tetrahedra due to irradiation, and also typically include interstitial type Shockley partial and Frank type dislocations. In BCC materials typically form interstitial 1/2$\langle$1 1 1$\rangle$ dislocations, but vacancy type 1/2$\langle$1 1 1$\rangle$ dislocations were also observed in V and Nb. HCP materials tend to form complex dislocation structures mainly consisting of a-type dislocations that can be of both vacancy or interstitial type. Correlations between saturated defect concentrations and fundamental underlying material properties are explored.
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Materials Science
Beyond special quasirandom structures: free energies from energy cumulants
Yann L. Müller and Anirudh Raju Natarajan
Predicting the finite-temperature stability of a disordered phase requires its free energy. It is traditionally approximated by combining the energy of a special quasirandom structure (a small
cell mimicking a random
alloy) with the ideal configurational
entropy. This approximation neglects the short-range order that develops on cooling. In this study, we show that the conventional approximation is the first term of an infinite expansion of the free energy in energy cumulants. Higher-order cumulants are estimated from energies of random arrangements, without Monte Carlo or molecular dynamics. In a nine-element refractory system, adding the second cumulant reduced free energy errors by about an order of magnitude. The expansion gives phase diagrams with order–disorder transitions, defect concentrations, and short-range order. To demonstrate its utility, we used a foundation interatomic potential to screen lithium-excess rocksalt oxides across 26 elements for synthesizable disordered phases rich in the Li$_4$ clusters needed for lithium percolation. The approach applies to any
lattice and chemistry, and brings disordered phases within reach of routine screening.
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Materials Science
Benchmarking Universal Machine-Learning Interatomic Potentials for Temperature-Dependent Elasticity of Binary and High-Entropy Refractory Carbides
Miroslav Lebeda, Jan Drahokoupil, Šimon Svoboda et al. (+1 more)
Accurate prediction of temperature-dependent elasticity is important for assessing refractory carbides under high-temperature conditions, but the computational cost of ab initio molecular dynamics (AIMD) limits systematic investigations across compositions and temperatures. Universal machine-learning interatomic potentials (uMLIPs) offer an efficient alternative, yet their accuracy for this task remains insufficiently established. Here, we
benchmark nine uMLIPs against consistent AIMD reference data for five binary and two high-
entropy (HE) carbides between 300 and 1200 K. Elastic constants and the corresponding bulk, shear, and Young's moduli are obtained using stress-strain molecular dynamics, explicitly sampling thermal atomic motion and anharmonic effects beyond thermal expansion alone. We assess absolute elastic properties and normalized thermal softening separately. MACE-MH-1 achieves the lowest overall mean absolute percentage error (5.7%). MACE-MH-1 and DPA4-Mini reproduce thermal softening most accurately, with mean deviations of 2.5 and 2.3 percentage points, respectively. All models generally underestimate stiffness, with larger
equilibrium volumes relative to the AIMD reference likely contributing to this trend for most models. C12 exhibits the largest model-dependent errors. The HE carbides are described with accuracy comparable to that of the binary carbides, indicating no apparent accuracy penalty from chemical complexity. Accuracy instead varies with transition-metal composition, with group-V carbides, particularly TaC, presenting the greatest challenge. These results identify promising pretrained models for finite-temperature elasticity in carbides and show why accurate absolute stiffness and thermal softening must be assessed independently.
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All authors Miroslav Lebeda, Jan Drahokoupil, Šimon Svoboda, Petr Vlčák
Materials Science · Cross-listed from cond-mat.mes-hall
Tunable Ultrastrong Magnon-Magnon Coupling and Squeezed States in a Triaxial Van der Waals Antiferromagnet
Xiao Xiao, Zishuang Li, Zui Tao et al. (+6 more)
Achieving and quantifying ultrastrong
magnon-
magnon coupling (USC) remains a key challenge for
quantum magnonics. Here, we demonstrate widely tunable USC between chiral (right- and left-handed) and acoustic or optical
magnon modes in the van der Waals antiferromagnet $CrPS_4$. Using a full
quantum model, we decompose the interaction into three microscopic interaction channels: the co-rotating term $g_1$ (mode hybridization), the counter-rotating term $g_2$ (two-mode squeezing), and, uniquely in the chiral regime, the self-squared term $g_3$ that mediates single-mode squeezing. The normalized coupling ratio reaches $g/f_g$ $\sim$ 0.41, entering the USC regime. Most significantly, we establish a complete protocol linking these USC parameters to a measurable
quantum phenomenon: a squeezed
magnon vacuum state. Our simulations not only visualize the chirality and polarization
evolution of the hybrid modes but also demonstrate how to directly extract quadrature fluctuations and a substantial squeezing factor (up to $\sim$ 9.7 dB) from thermal noise-driven magnetization dynamics. This work provides a material-specific
quantum framework for USC and a practical pathway to detect and exploit non-classical
magnon states in low-damping two-dimensional magnets, opening a route toward
quantum-enhanced spintronics and hybrid
quantum information platforms.
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All authors Xiao Xiao, Zishuang Li, Zui Tao, Lina Chen, Ping Liu, Shuai Zhang, Haozhe Wang, Yong Pu, Ronghua Liu
Materials Science · Cross-listed from cond-mat.str-el
Magnon band splitting without altermagnetism in CuF2
Ioannis Rousochatzakis, Oleg Janson and Alexander A. Tsirlin
Conclusive identification of an altermagnetic state requires going beyond mere
symmetry arguments. We illustrate this in a combined computational and experimental study of the rutile-like material CuF$_2$, which is on the list of predicted altermagnets. Using ab initio and linear
spin-wave calculations supplied by magnetization measurements, we show that CuF$_2$ in its experimental monoclinic structure can be described by a
spin-$\frac12$ model of weakly coupled square-
lattice layers with the in-plane coupling $J_1\simeq 115$ K and two synergistic antiferromagnetic interplane couplings amounting to 4% and 8% of $J_1$, respectively. Driven by long-range superexchange, these interlayer couplings are oblique to the square planes, resulting in the unit-
cell doubling in the magnetically ordered state, thus effectively suppressing any altermagnetic band splitting. Concurrently, we identify unusually strong Dzyaloshinskii-Moriya interactions, $|\mathbf D|/J_1\simeq 0.3$, that produce
spin canting and, together with order-by-disorder effect, pin the Néel vector to the crystallographic $b$-axis. Additionally, DM anisotropy promotes
magnon band splitting, but these bands remain non-chiral. Our results highlight the importance of relativistic effects even in $3d$ magnets with altermagnetic
symmetries.
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Materials Science
Solution-Based Synthesis of Fe-Co-Ni Prussian Blue Analogue Powders: A Comparative Structural, Spectroscopic and Thermal Study
Larissa de O. Garcia, Lindiomar Borges de Avila Jr, Mengmeng Wang et al. (+3 more)
Prussian Blue (Fe-PBA) and its Co and Ni analogues (Co-PBA and Ni-PBA) were synthesized by an additive-free aqueous co-precipitation route using K$_4$[Fe(CN)$_6$] and FeCl$_3$, CoCl$_2$, or NiCl$_2$, respectively. The three powders were systematically compared by X-ray diffraction, ATR-FTIR and Raman spectroscopy, FEG-SEM/EDS, and TG/SDTA. All compositions exhibit the characteristic cubic cyanide-bridged PBA framework, with apparent
lattice parameters of 10.10 +/- 0.02, 10.01 +/- 0.02, and 10.10 +/- 0.03 Angstrom for Fe-PBA, Co-PBA, and Ni-PBA, respectively. The dominant C$\equiv$N stretching band in ATR-FTIR shifts from 2062 to 2071 and 2087 cm$^{-1}$ across the Fe-Co-Ni series, indicating composition-dependent changes in the local cyanide environment. Fe-PBA contains less potassium than the Co- and Ni-containing powders and exhibits a substantially larger low-temperature mass loss. Sharp reflections assigned to crystalline KCl are observed in all three diffraction patterns, while additional unassigned reflections in Ni-PBA indicate the presence of at least one further crystalline phase. These results show that differences among Fe-, Co-, and Ni-based PBAs cannot be attributed solely to transition-metal identity, as precursor oxidation state and washing efficiency also influence the composition and thermal response of the resulting powders.
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All authors Larissa de O. Garcia, Lindiomar Borges de Avila Jr, Mengmeng Wang, Yann Garcia, Christian K. Muller, Flavio Abreu Araujo
Materials Science
Photoinduced Odd- and Mixed-Parity Magnetism in Collinear Antiferromagnets
Jin-Yang Li, Ruo-Yu Ning, Ying Zhang et al. (+3 more)
Altermagnetism, characterized by compensated collinear
magnetic moments in real space and momentum-dependent
spin splitting with even-parity
symmetry, has recently emerged as a distinct form of
magnetic order beyond the conventional ferro- and antiferromagnetic paradigms. However, realizing odd- and mixed-parity magnetism in fully compensated collinear magnets remains challenging. Here, we demonstrate that light irradiation can induce odd- and mixed-parity magnetism in conventional collinear antiferromagnets. Taking monolayer CoS and CoSe as representative systems, and combining Floquet theory with first-principles calculations, we show that circularly polarized light (CPL) induces odd-parity $f$-wave
spin splitting, whereas elliptically polarized light (EPL) induces odd-parity $p$-wave
spin splitting. Uniaxial strain combined with CPL provides an alternative route to realizing the $p$-wave state. More remarkably, applying an electric field together with CPL or EPL transforms the
spin splitting into mixed-parity forms. The light-induced breaking of $\mathcal{PT}$
symmetry, together with
spin-orbit coupling, further gives rise to a finite anomalous Hall response. Our work establishes a versatile strategy for engineering odd- and mixed-parity
spin splitting in compensated antiferromagnets, offering a route toward light-controlled electronic and
magnetic phenomena.
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All authors Jin-Yang Li, Ruo-Yu Ning, Ying Zhang, Qiu-Qiu Li, Si Li, Wen-Li Yang
Materials Science · Cross-listed from physics.chem-ph
Optical absorption spectra from the $GW$-Bethe-Salpeter framework for thousands of atoms
Maximilian Graml, Ritaj Tyagi, Rémi Pasquier et al. (+2 more)
The frequency-dependent absorption and emission of light determine the colors of matter and underpin today's technologies, from solar
cells to light-emitting diodes. Predicting optical properties from first principles remains a computational challenge, especially for large and disordered systems. The $GW$ plus Bethe-Salpeter equation ($GW$-BSE) approach provides predictive accuracy for optical properties, but conventional implementations become costly as system size grows. Here, we present a $GW$-BSE framework combining real-time propagation, atom-centered basis sets, and a locally optimized real-space resolution of the identity. The cost of each propagation step scales quadratically with system size and roughly equals the cost of one self-consistent-field iteration in a density-functional calculation with a semilocal functional. This computational efficiency allows us to calculate the absorption spectrum of a nanographene containing 4616 atoms and opens a path toward routine calculations of optical properties for large disordered systems.
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All authors Maximilian Graml, Ritaj Tyagi, Rémi Pasquier, Štěpán Marek, Jan Wilhelm
Materials Science
Can end-to-end learning from raw electronic structure explain magnetic anisotropy?
Rafał Topolnicki, Jan Navrátil and Piotr Błoński
Machine-learning models trained directly on electronic spectra can predict
spin–orbit-driven properties, yet models with comparable predictive accuracy may learn different electronic dependencies. We examine this problem using
magnetic anisotropy in atomic-scale magnets and a validation strategy designed to assess the physical relevance of learned spectral relationships. We compare a bidirectional gated recurrent unit and a one-dimensional convolutional neural network, both trained to predict
magnetic anisotropy energy (MAE) from
spin- and orbital-resolved scalar-relativistic densities of states (SR-DOS). Despite comparable in-domain (ID) accuracy, the architectures learn only partly overlapping spectral dependencies. Shapley additive explanations identify spectral features shared between the two architectures that can be associated with plausible
spin–orbit-coupling pathways consistent with second-order perturbation theory (PT2). Adding PT2-derived MAE contributions to the model inputs has little effect on ID performance but can improve transfer beyond the training domain, with gains differing between architectures. Controlled spectral perturbations further demonstrate that similar attribution patterns do not imply the same functional dependence of the predicted MAE on spectral weight. The contrasting responses provide a functional context for architecture-dependent out-of-domain transfer. End-to-end learning can identify candidate electronic signatures of
magnetic anisotropy. Their credible microscopic interpretation, however, rests on convergent evidence from predictive performance, model comparison, physical theory, controlled spectral interventions, and evaluation under distribution shift.
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Materials Science
A General Algorithm for Minimal Uncoupled Stress–Strain Calculations of Elastic Constant
S. I. Simak and Utkarsh Singh
We have developed a general
algorithm for constructing the minimum number of strain configurations required to extract second-order elastic constants from first-principles stress-strain calculations without algebraic coupling between the constants targeted for extraction. The method operates on the sparsity structure of the
symmetry-reduced elastic stiffness
matrix, represented by an auxiliary binary
matrix, and generates admissible strain patterns algorithmically rather than prescribing separate strain sets for individual
crystal symmetries. Each independent elastic constant is obtained from a single stress component, while additional stress relations generated by the same deformation provide internal consistency checks. Because the six-dimensional strain space contains only 2^6-1=63 non-empty strain patterns, the minimality of the resulting sets can be verified exactly for every elastic-
symmetry type considered. The construction reproduces established high-efficiency strain sets in cases where they are minimal and yields improved sets for
symmetry classes in which previously tabulated schemes require additional configurations. Because the formulation is based on stress-strain derivatives, it can also be readily extended to finite temperatures using consistently sampled ensemble-averaged thermodynamic stresses. Explicit strain sets are derived for all elastic-
symmetry types spanning the 230 crystallographic space groups, and their accuracy and computational efficiency are benchmarked against established approaches.
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Materials Science
Interlayer ferromagnetic order revealed through pressure-enhanced interlayer exchange coupling in Fe$_3$GaTe$_2$
Riku Iimori and Takashi Kimura
Van der Waals ferromagnets possess finite interlayer
magnetic coupling despite their layered
crystal structures, and this coupling plays an important role in determining their
magnetic properties. In this study, we performed magnetization measurements on high-quality Fe$_3$GaTe$_2$ single
crystals while selectively tuning the interlayer coupling using hydrostatic pressure. We identified two characteristic temperatures, $T_{\rm inf1}$ and $T_{\rm inf2}$, below the Curie temperature with opposite pressure dependences: $T_{\rm inf1}$ is associated with thermally activated domain-wall depinning, whereas $T_{\rm inf2}$ reflects the formation of interlayer ferromagnetic order. Both temperatures exhibit pronounced pressure dependences, in sharp contrast to the nearly pressure-independent Curie temperature associated with intralayer ferromagnetic order. First-principles calculations revealed a substantial pressure-induced enhancement of the interlayer exchange interaction and reasonably reproduced $T_{\rm inf2}$ and its pressure dependence. These results demonstrate that the emergence of interlayer
magnetic ordering can be predicted from the microscopic interlayer exchange coupling, establishing a predictive framework for understanding and designing interlayer coupling phenomena in layered
magnetic materials.
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Materials Science
Predicting plasmonic pole representations of complex dielectric spectra using convolutional neural networks
Dario A. Leon
Extracting spectral properties such as energy position, broadening, and spectral weight from dielectric spectra is critical for interpreting collective electronic excitations in many-body physics. Conventional approaches typically rely on nonlinear fitting procedures that can be computationally demanding and highly sensitive to initialization and fitting choices. In this work, we develop a convolutional neural-network framework for the direct inversion of dielectric spectra into their underlying plasmonic pole structures using a multipole-Padé representation. Rather than training on a constrained database of spectra associated with a specific set of materials, the network is trained entirely on synthetic spectra generated from the analytical multipole-Padé expression with randomized parameters. This enables the network to learn the general mapping between the spectra and their features in an unbiased way, without requiring large, material-specific
datasets derived from real materials. We demonstrate that the synthetically trained network generalizes to complex first-principles and experimental dielectric spectra, extracting the underlying pole parameters with high accuracy in a single forward pass. This approach provides an efficient and robust alternative to conventional nonlinear fitting, enabling high-throughput, automated analysis of dielectric spectra across diverse materials and applications.
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Materials Science
Mode-selective electron-phonon coupling drives charge density waves in the kagome metals YRu$_3$Si$_2$ and LaRu$_3$Si$_2$
Wenqian Tu, Run Lv, Dingfu Shao et al. (+2 more)
YRu$_3$Si$_2$ and LaRu$_3$Si$_2$ host the highest charge density wave (CDW) transition temperatures ever reported in kagome metals, $T_{\mathrm{CDW}}\approx 800$ and 400~K, with propagation vectors $Q_{\mathrm{CDW}}\approx(1/2,0,0)$ and $(1/4,0,0)$, respectively. The microscopic mechanism behind these record values has remained unresolved. Here, we combine anharmonic
phonon renormalization extracted from molecular dynamics driven by a machine-learned force field with mode-resolved electron-
phonon coupling (EPC) analysis to identify this mechanism. The CDW is driven by mode-selective EPC: the Ru out-of-plane
phonon modes couple the Ru-$d_{xz}/d_{yz}$ and Si-$p_x/p_y$ orbitals, and the
phonon linewidth peaks sharply at $Q_{\mathrm{CDW}}$, while the featureless electronic susceptibility rules out Fermi-surface nesting.
Phonon anharmonicity melts the CDW, and the anharmonic
phonon spectra reproduce both $Q_{\mathrm{CDW}}$ and $T_{\mathrm{CDW}}$ in good agreement with experiments. Molecular dynamics simulations also visualize the CDW melting in real space. Chemical bonding analysis further shows that the smaller Y$^{3+}$ radius strengthens the Ru-Ru bonds, enhancing
lattice rigidity and accounting for the factor-of-two higher $T_{\mathrm{CDW}}$ of YRu$_3$Si$_2$. Our results establish a unified microscopic picture of CDW formation and melting in kagome metals YRu$_3$Si$_2$ and LaRu$_3$Si$_2$.
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All authors Wenqian Tu, Run Lv, Dingfu Shao, Yuping Sun, Wenjian Lu
Materials Science
Robust skyrmion nucleation and transport via composition gradient in rare earth-transition metal ferrimagnets
Pietro Diona, Luca Maranzana and Sergey Artyukhin
Magnetic skyrmions are typically nucleated via localized excitation methods, such as
laser heating,
spin-orbit torques, or engineered defects, and their controlled transport is often limited by the skyrmion Hall effect. Here, we demonstrate that spatial gradients in rare-earth–transition-metal
alloys, achievable through patterned
laser writing, enable both deterministic nucleation and controlled transport. The strategy leverages engineered compositional gradient to cross the magnetization compensation point, defining regions with opposite magnetization. An out-of-plane
magnetic field selectively reverses the magnetization, generating a skyrmion. Crucially, the same compositional design enables a channel tuned to the
spin angular momentum compensation point, where skyrmions are driven by
spin-orbit torques at high velocity with vanishing skyrmion Hall effect. Local composition variations act as pinning sites, enabling threshold-controlled trapping and release.
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Materials Science
Epitaxial growth of WO3 on r-plane sapphire by hot-filament metal-oxide deposition using CO2 as a precursor
Laurent Souqui, Lewis J. Adams, Andreas Tsampanakis et al. (+2 more)
The deposition of epitaxial films of WO3 by hot-filament metal-oxide deposition using CO2 as a precursor was demonstrated. The films were obtained at a low growth rate of 0.25 nm/min. The optical properties of the film were assessed by variable-angle spectroscopic ellipsometry, indicating transparency across the visible spectrum and high absorption above 3 eV.
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All authors Laurent Souqui, Lewis J. Adams, Andreas Tsampanakis, David Rehnlund Maibach, Per Eklund
Materials Science
The role of density in shaping electron trapping in amorphous silicon nitride
Jonathon Cottom and Emilia Olsson
The electronic properties of amorphous silicon nitride vary with processing, which often changes stoichiometry and density together. Separating their contributions is essential to connect film structure with electron trapping. Across 499 stoichiometric configurations spanning 2.86-3.19g cm$^{-3}$, porosity controls the trapping mixture. Lower density increases accessible void fraction from 8.4 to 12.6%, expands internal surface and more than triples the supply of free three-coordinate Si precursors. Capture at pre-existing Si dangling bonds (K centres) rises from 9 to 29%, while induced-K and polaronic trapping decline. A neutral precursor fingerprint predicts the trapping mixture in held-out configurations and reproduces its density dependence. Local compensation controls K-centre activation, electronic competition selects capture, and bond strain predicts polaronic relaxation or induced-K formation. Routes involve distinct network volumes but retain their characteristic depths and relaxation energies across the density range. At fixed stoichiometry, density controls the trapping mixture through porosity and precursor availability.
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Materials Science
Probing $L_z$ Orbital Angular Momentum via Wavefunction-Interference-Induced Charge Order
Jonas Erhardt, Sven Schemmelmann, Fabian Schöttke et al. (+9 more)
Orbital angular momentum (OAM) characterization is central to understanding
quantum materials such as valley Hall and Rashba systems and, through its connection to Berry
curvature, provides key insight into band
topology. Conventional OAM detection via photoemission dichroism, however, is susceptible to interference artifacts and is largely restricted to occupied states. Here, we demonstrate a real-space approach to map the $L_z$ OAM character using scanning tunneling microscopy in triangular atomic monolayers. Unlike photoemission, this method exploits interference effects arising from the $L_z$ orbital phase and the Bloch phase associated with neighboring atoms. This shifts the local density of states (LDOS) maxima to distinct Wyckoff positions between atoms, encoding $L_z$ information into characteristic real-space LDOS patterns. We exemplify this approach in 2D
quantum materials with contrasting $L_z$ sequences, namely Tl/Si(111) and In/SiC(0001) monolayers, identifying $L_z$-dependent LDOS accumulation associated with distinct topological phases in both systems. Our results establish $L_z$-dependent charge localization as a proxy to atomic obstruction for energetically isolated states in triangular
lattices, including transition-metal dichalcogenides.
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All authors Jonas Erhardt, Sven Schemmelmann, Fabian Schöttke, Cedric Schmitt, Lukas Gehrig, Bing Liu, Domenico Di Sante, Giorgio Sangiovanni, Jörg Schäfer, Peter Krüger, Markus Donath, Ralph Claessen
Materials Science
Achieving room temperature plasticity in TiO2 ceramics by flash processing
Xinghua Su, Zhenyu Li, Xufei Fang et al. (+3 more)
Ceramics are indispensable materials for modern engineering and high-technology applications. However, the intrinsic brittleness at room temperature can cause catastrophic failure and severely limit their widespread applications. Here, we report a flash processing (FP) method based on the coupling of electric and thermal fields to significantly improve the room-temperature plasticity of TiO2 ceramics with a large plastic compressive strain of 15.4% during micropillar compression. This large room-temperature plasticity is attributed to the proliferation of stacking faults and twin boundaries during the loading process, which may be assisted by the high concentration of oxygen vacancies introduced by the FP method. Our findings suggest that FP can be a simple and effective method for achieving improved room-temperature plasticity of ceramic materials through defect engineering.
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All authors Xinghua Su, Zhenyu Li, Xufei Fang, Wenjun Lu, Mengyao Wang, Peng Zhao
Materials Science
Demonstration of ultrafast coherent sub-picosecond magnon pulses
Peter Kubaščík, Miina Leiviskä, Martin Bušina et al. (+20 more)
Ultrafast magnonics explores routes towards energy-efficient information processing by replacing electrons with pulses of terahertz
magnons. The critical, but so far elusive, requirement on the
magnon pulses is the combination of high-speed and a long-range propagation while maintaining a well-defined narrow waveform of the pulses. Here, we demonstrate the launching of 0.4-picosecond
magnon pulses in the altermagnetic
insulator $\alpha$-Fe$_2$O$_3$ (hematite) using broadband terahertz
spin-orbit torques by an adjacent platinum layer. Phase-resolved terahertz transmission reveals that these sub-picosecond pulses travel ballistically, coherently and non-dispersively at a constant velocity of 23 nm/ps, transport angular momentum and retain their temporal waveform shape over 160 nm, with an inferred relaxation length in hundreds of nanometers or more. Beyond establishing $\alpha$-Fe$_2$O$_3$ as an optimal platform for ultrafast magnonics, our technique introduces a high-resolution, tabletop method to directly extract dispersion relations up to high wavevectors, and explore ultrafast
magnon dynamics in altermagnets and other
magnetic materials with teraherz-range dynamics.
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All authors Peter Kubaščík, Miina Leiviskä, Martin Bušina, Zdenek Kašpar, Katharina Müller, Jonathan Mak, Monika Scheufele, Gal Lemut, Jose Solano, Oliver Franke, Rostislav Matuška, Jiří Jechumtál, Eva Schmorranzerová, Petr Němec, Petr Kužel, Tobias Kampfrath, Piet W. Brouwer, Matthias Opel, Stephan Geprägs, Matthias Althammer, Tomáš Jungwirth, Helena Reichlova, Lukáš Nádvorník
Materials Science · Cross-listed from cs.AI
AtomWorld-Mirror: Macro-Step World Modeling of Critical Evolution Backbones for Materials Dynamics
Ziming Pan, Ruge Zhang, Haozhi Han et al. (+7 more)
Atomistic simulation is a fundamental tool for studying long-term materials
evolution, from
diffusion and defect dynamics to interfacial reactions and fracture. Yet conventional simulators typically advance at microscopic resolution, spending substantial computation on low-impact local updates before reaching structurally consequential states, an evolutionary-resolution bottleneck that limits long-horizon simulation. We propose AtomWorld-Mirror, a time-aware macro-step world model for the critical
evolution backbone of atomic systems. For Step-Wise atomistic simulation, AtomWorld-Mirror distills short micro-event segments into physically reachable transitions between key states, jointly predicting sparse structural edits and accumulated physical time through latent macro-step dynamics. Local reachability, inventory conservation, and continuous-time consistency constrain each transition. By amortizing local atomic physics into a reusable latent macro model and replacing explicit micro-event replay with macro-step inference, this formulation provides a path toward substantially faster prediction of long-term materials
evolution while preserving structural validity and time semantics. Across five atomic systems, spanning Cu-rich RPV steel irradiation aging, Cu-Zr metallic glass, and Li$_3$N-based anti-perovskite solid electrolyte, macro-step inference delivers a speed up of $10^3$ to $10^4$ times over event-by-event simulation.
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All authors Ziming Pan, Ruge Zhang, Haozhi Han, Junkai Zhou, Xingyuan Chen, Yifeng Chen, Yunquan Zhang, Ting Cao, Yunxin Liu, Kun Li
Materials Science
Effects of chlorine substitution on the magneto-optical properties of CrSBr
Z. Śnioch, R. Komar, M. Kuna et al. (+7 more)
We present a systematic study of the effects of chlorine substitution on the magneto-optical properties of the van der Waals layered
semiconductor CrSBr. Our study shows that even at substitution level of $x=56\%$ the $\mathrm{CrSBr_{1-x}Cl_{x}}$ material exhibits qualitatively the same clear magneto-optical coupling that was observed in pure CrSBr
crystals. The values of the relevant parameters are shown to vary smoothly across different substitution levels, thus offering promising tunability for this family of 2D
magnetic materials.
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All authors Z. Śnioch, R. Komar, M. Kuna, M. Raczyński, K. Mosina, A. Söll, Z. Sofer, K. Wohlfeld, P. Kossacki, T. Kazimierczuk
Materials Science
Generation, Accumulation, and Utilization of Data in the Automatically Controlled End-Station of a Soft X-ray Beamline
Yasunobu Ando, Masashige Miyamamoto, Keita Hiromori et al. (+4 more)
AI is rapidly transforming materials exploration, yet reliable AI-assisted research depends on experimental data that retains their context, provenance, and machine-readable structure. High-throughput synchrotron measurements therefore require more than automated data acquisition: data generation, accumulation, and utilization must be connected within a continuous workflow. Here, we present a data-centric research framework that integrates the PIONEER system, the OMNES, and ML analysis. The PIONEER system automates sample handling,
vacuum transfer, and scanning XAS at the BL08U soft X-ray beamline of NanoTerasu, systematically generating large volumes of spatially resolved spectral data. Measurement and analysis files are stored in the cloud-based ARIM-mdx data system, while OMNES manages metadata describing samples, preparation procedures, measurement conditions, instrument settings, data locations, and analysis histories. Tabular and JavaScript Object Notation formats are used according to the metadata structure, with numerical values stored separately from units to facilitate machine processing. OMNES organizes these records based on causal relationships among experimental and analytical processes, linking samples, measurements, raw data, processed data, and analysis results through a relational data model and visualizing their relationships as a graph. This causality-based organization preserves experimental and analytical provenance and clarifies how each result was derived from the preceding processes and data. The accumulated spectra can subsequently be processed using ML methods, including dimensionality reduction and materials classification, and the resulting data can be registered back into OMNES. Previously reported ML analysis of BN XAS spectra is presented as an example of the analytical workflow that can be applied to data acquired at the beamline.
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All authors Yasunobu Ando, Masashige Miyamamoto, Keita Hiromori, Takeru Nakashima, Masafumi Horio, Masato Kotsugi, Iwao Matsuda
Materials Science · Cross-listed from physics.app-ph
Time-Domain Analysis of Surface Acoustic Wave Magnetoelectric Sensors
Mohsen Samadi, Henrik Wolframm, Felix Weisheit et al. (+4 more)
The transient response of surface acoustic wave sensors is important for understanding their dynamic behavior, propagation delay, and response to time-varying signals. In this work, the time-domain propagation characteristics of a magnetoelectric SAW sensor based on a multilayer Love-wave delay line are investigated using complementary numerical and experimental approaches. Time-domain analysis is employed to determine the delay time and to extract the phase and group velocities, while frequency-domain analysis provides an independent characterization of the wave dispersion. Both numerically and experimentally, the phase and group velocities are found to differ, reflecting the dispersion of the Love wave in the multilayer structure. At the operating frequency of 146 MHz, the simulated group velocity obtained from wave-field tracking agrees within 0.4% with the value determined from the frequency-domain dispersion relation. The simulated delay time and group velocity also show good agreement with experiment, with deviations of 2.7% in delay time and 0.9% in group velocity. These results demonstrate the consistency of the time- and frequency-domain analyses and provide a quantitative characterization of the transient propagation behavior of SAW sensors.
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All authors Mohsen Samadi, Henrik Wolframm, Felix Weisheit, Dirk Meyners, Eckhard Quandt, Michael Höft, Martina Gerken
Materials Science · Cross-listed from physics.ins-det
Autocorrelation-based beam shape optimization in scanning electron microscopy
Rebecca Guan, Andreas Werbrouck, Matthew M. Maschmann et al. (+1 more)
Many automatically focusing
algorithms for scanning electron microscopes exist. Typically, these optimize a single derived metric (such as image sharpness) without considering the intrinsic beam shape. We describe an
algorithm to automatically focus and stigmate scanning electron microscopes based on the autocorrelation of captured images. In the first part of this work, we develop the theoretical basis of using the autocorrelation to approximate the current beam shape. In the second part, we use this to condition the beam shape on various surfaces, using
Bayesian optimization to tune both working distance and, in particular, stigmation. Through a comparison of the full width at half maximum of the autocorrelation arrays before and after optimization and a visual comparison of images taken of the sample surface before and after optimization, we show that the
algorithm is able to successfully optimize the scanning parameters. Overall, our
algorithm can effectively focus on a variety of topographies at different magnifications.
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All authors Rebecca Guan, Andreas Werbrouck, Matthew M. Maschmann, Matthias J Young
Materials Science
Data-Driven Variable-Exponent Analysis for Photoemission Yield Spectroscopy: An Autonomous Self-Diagnosing Framework Based on Integrated Residual Metrics
Shinjiro Yagyu, Takahiro Nagata and Yoshiyuki Nakajima
Photoemission yield spectroscopy (PYS) is widely used for evaluating the electronic states of materials. As automated materials discovery advances, unsupervised extraction of physical information from ambient-air PYS data becomes important. Conventional fixed-exponent analyses and logarithmic transformations suffer from heteroscedasticity, which destabilizes estimation in low-signal regions. To address this, we propose a data-driven analysis framework based on the 1/n-Scan method, which operates directly in the original signal space, removing the
geometric bias inherent in log-transform approaches. We further integrate a self-diagnostic quality-evaluation system that quantifies estimation uncertainty with Akaike weights, together with independent residual metrics–the normalized mean absolute error (NMAE), the RMSE-to-MAE ratio (RMR), the Durbin-Watson (DW) statistic, and a macroscopic metric ($\Delta R^2$)–that distinguish hardware-related data degradation from a physical-model mismatch. Applying the framework to differently doped Si and a polycrystalline Au reference in air, we demonstrate autonomous detection, without assumptions on the emission mechanism, of the breakdown of the single-component approximation in heavily doped p-type Si, arising from the overlap of two emission components with different thresholds, as a statistical anomaly–a decrease in DW below its critical value with an auxiliary increase in $\Delta R^2$, despite sound NMAE and RMR–independently confirmed by a two-component fit ($\Delta$AIC $\approx$ 57, DW recovering from 0.8 to 2.0). For heavily doped n-type Si, the gradual surface
evolution was classified as a change within the single-component description. This framework provides a robust, self-diagnosing analysis engine for closed-loop autonomous materials exploration.
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Materials Science · Cross-listed from cond-mat.mes-hall
Displacement-Field-Induced Ionization of Defect States in High-Quality hBN
Ilia Begichev, Daria Belotcerkovtceva, Iakov Reznikov et al. (+10 more)
Encapsulation of two-dimensional (2D) materials with hexagonal boron nitride (hBN) is widely used to fabricate ultraclean van der Waals (vdW)
heterostructures for optoelectronic and
quantum transport studies. These devices are often operated under strong out-of-plane displacement fields that tune the electronic properties of the active 2D material, while the surrounding hBN is typically assumed to remain electronically inert. This assumption, however, neglects defect states that are present even in high-quality hBN
crystals. Here, we probe their response to the applied displacement field using monolayer
graphene encapsulated between hBN
crystals as a sensitive charge sensor. Increasing the displacement field induces notable charge transfer between
graphene and hBN, producing additional electron doping of 10-20x10^9 cm^(-2) even at the moderate displacement field (~0.5 V nm^(-1)), while simultaneously increasing carrier-density inhomogeneity of the
graphene layer. Both effects are consistent with ionization of defect states within the hBN bandgap, with the bulk density ~1-7x10^(-5) nm^(-3) varying across different hBN
crystals. Our results show that displacement-field-induced defect ionization in hBN can modify the electronic response of vdW
heterostructures, with direct implications for device design and interpretation of experiments.
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All authors Ilia Begichev, Daria Belotcerkovtceva, Iakov Reznikov, Sergey Slizovsky, Weijie Lu, Nansi Zhou, Ian Babich, Makars Siskins, Kostya S. Novoselov, Vladimir I. Falko, Kenji Watanabe, Takashi Taniguchi, Alexey I. Berdyugin
Materials Science
Multifunctionality in Janus CrMCN4 (M = Si/Ge) Monolayers: Valleytronic Physics, Piezoelectric Response, and Photocatalytic Potential
Jubair Hossan Abir, M.R.U.S. Shapon, S.S.B. Pallab et al. (+3 more)
Two dimensional Janus
semiconductors integrating
spin-valley coupling, piezoelectricity, and tunable optical responses offer a platform for multifunctional nanodevices. Here, first-principles calculations reveal complementary composition and strain effects in CrSiCN4 and CrGeCN4 monolayers. Both are found to be nonmagnetic direct-gap
semiconductors, with gaps of 1.23 and 1.09 eV using the Perdew-Burke-Ernzerhof functional including
spin-orbit coupling, respectively. HSE06 hybrid-functional calculations retain the direct-gap character, yielding gaps of 1.46 eV for CrSiCN4 and 1.19 eV for CrGeCN4. Opposite out-of-plane
spin character and Berry
curvature emerge at K and K'. Biaxial strain reduces the respective gaps from 1.59 to 0.86 eV and 1.44 to 0.63 eV, drives direct-to-indirect transitions, and
redshifts absorption while preserving valley
spin contrast. CrGeCN4 exhibits larger in-plane piezoelectric response, whereas CrSiCN4 exhibits larger out-of-plane magnitude. Band-edge
alignment satisfies the oxygen
evolution reaction requirement but provides insufficient driving force for the hydrogen
evolution reaction, motivating further strain-induced band-edge modulation toward overall water splitting. These results establish composition and strain as complementary controls for tailoring Cr-based Janus monolayers for valleytronic, optoelectronic, electromechanical, and photocatalytic applications.
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All authors Jubair Hossan Abir, M.R.U.S. Shapon, S.S.B. Pallab, Tanvir Khan, Raihana Shams Islam, Saleh Hasan Naqib
Materials Science
A hinged honeycomb with zero bulk modulus retaining more than four-fifths of its constituent's shear modulus
Chun-Teh Chen
A Poisson's ratio near -1 indicates only that the bulk modulus is small compared with the shear modulus. In solid-void structures, the mechanism that frees the dilation usually weakens the resistance to shear as well, resulting in both moduli becoming small. In two-dimensional linear elasticity, we demonstrate that this loss is not inevitable. We consider a honeycomb of regular hexagonal blocks of a single incompressible isotropic elastic solid, joined along their whole edges by ideal interfaces that allow relative sliding along a direction inclined to the edge normal. Collective infinitesimal block rotations produce an exact dilational mechanism, so the effective bulk modulus vanishes, while sixfold
symmetry ensures isotropy. The interfaces, however, transmit traction along their whole length. In a solid-void realization, each interface is replaced with fine solid plates separated by void, which bend easily yet retain their capacity to transmit axial force. Such dilational materials, which expand or contract freely while resisting every change of shape, could serve as interlayers that accommodate thermal or swelling mismatch while still transmitting shear, and as components in stents and deployable structures that change size without changing shape. An explicit, statically admissible stress field and the complementary energy principle yield a rigorous lower bound on the retained shear modulus, and a limiting argument transfers this bound to the solid-void mixtures. The honeycomb retains more than four-fifths of its constituent's shear modulus at zero bulk modulus: the supremum S of the normalized shear modulus of such mixtures satisfies S > 0.8528 > 4/5, exceeding the value attained by Milton's construction.
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Materials Science · Cross-listed from cond-mat.supr-con
High-Efficiency and Large Supercurrent Rectification with Superconducting Coil
Takumi Ichikawa, Daisuke Takegami, Gen Nishijima et al. (+8 more)
Superconducting diodes (SDs) are devices that rectify supercurrent through the difference in the superconducting critical current (Ic) between forward and reverse current directions. For bringing such SDs closer to practical superconducting power electronics applications, a combination of both high rectification efficiency ({\eta}) and a large Ic difference ({\Delta}Ic) is required. Here, we propose and demonstrate a coil-shaped superconducting wire device concept to induce a large SD effect, arising from the compensation between an external
magnetic field (Hext) and the field generated by the coil itself. From transport Ic measurements on coil-shaped SDs based on a Sn10-Pb90 solder wire, we achieved a {\eta} of 79% with a {\Delta}Ic of 140 A at Hext = 500 Oe (coil #2) and a {\eta} of 84% with a {\Delta}Ic of 125 A at Hext = 530 Oe (coil #3), confirming high rectification values at large supercurrents. The large-current high-efficiency SDE in the coil-shaped SDs will be highly useful for developing the potential field of supercurrent power electronics.
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All authors Takumi Ichikawa, Daisuke Takegami, Gen Nishijima, Shunsuke Kawakami, Tsutomu Nojima, Yuji Tsuchiya, Satoshi Awaji, Fuyuki Ando, Ken-ichi Uchida, Yuya Hattori, Yoshikazu Mizuguchi