Materials Science
Non-relativistic spin splitting in a triangular metal-excess magnet Fe$_{1+\delta}$Sb
Chao-Chun Wei, Xiaojuan Ni, Sophia Adams et al. (+5 more)
Non-relativistic
spin-splitting (NRSS) antiferromagnets have recently emerged as an important class of
magnetic materials that combine compensated magnetism with momentum-dependent
spin splitting, offering new opportunities for spintronic applications. Here, we investigate a NiAs-type Fe$_{1+\delta}$Sb series ($\delta = 0.17$-0.30) using
neutron diffraction, pair distribution function, magnetometry and density functional theory calculations.
Neutron diffraction establishes that Fe$_{1+\delta}$Sb adopts a $120^\circ$ coplanar compensated
magnetic order with a non-zero propagation vector $\mathbf{k}=(1/3,\,1/3,\,0)$. Increasing interstitial Fe suppresses the ordered
magnetic moment while inducing local
symmetry lowering, as revealed by pair distribution function refinements. Density functional theory predicts momentum-dependent
spin splitting, dominated by an out-of-plane
spin polarization with an odd-parity f-wave-like
symmetry, establishing the material as a non-collinear NRSS antiferromagnet. Motivated by the structural similarities between Fe$_{1+\delta}$Sb and a known altermagnet CrSb, we further investigate their solid solution and find that Cr substitution at intermediate concentrations gives rise to a ferromagnetic component and a cluster
spin-glass behavior. These results establish Fe$_{1+\delta}$Sb as a new platform for non-collinear NRSS antiferromagnetism and demonstrate metal interstitial and substitution as effective parameters for tuning the
magnetic order and properties.
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All authors Chao-Chun Wei, Xiaojuan Ni, Sophia Adams, Jacob Kjeldahl Jensen, Jue Liu, Qiang Zhang, Luisa Whittaker-Brooks, Huiwen Ji
Materials Science
A Large-scale Parallel Implementation of Quasi-Four-Component Relativistic Density Functional Theory with Numeric Atom-centered Orbitals
Wentao Zhang, Rundong Zhao and Volker Blum
We present a large-scale parallel implementation of fully relativistic density functional theory (DFT) for both molecules and periodic solids, using the quasi-four-component (Q4C) method and numeric atom-centered orbital basis sets. Our approach employs a domain decomposition method on nonuniform real-space integration grids, which enables order-N integration of the Q4C
Hamiltonian matrix elements using efficient, distributed-
memory and compute-parallel real-space operations. Next, we build the
Hamiltonian and overlap
matrices in a two-dimensional block-cyclic distribution layout. The resulting generalized
eigenvalue problems are solved with the massively parallel ELPA
eigenvalue solver library. We
benchmark memory usage, parallel efficiency, and scalability across multiple MPI tasks and compute nodes. This
algorithm extends the reach of fully relativistic DFT simulations for periodic solids, tested up to 3,383 atoms per unit
cell (216,628 basis functions) and likely still well below the true reach of the implementation. As a demonstration, we calculate the fully relativistic band structure for a 3,383 atom-per-unit-
cell doped hybrid organic-inorganic perovskite, (PEA)2(Pb1-xBix)I4 (PEA=phenethylammonium), showing nearly ideal scalability between 336 and 672 physical CPU cores.
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Materials Science
High-speed and high-gain graphene photovoltaic phototransistor gated by a van der Waals heterojunction
Yihan Yin, Jiayi Zhang, Xiaolong Zhang et al. (+5 more)
Two-dimensional (2D) material-based phototransistors offer a unique combination of optical sensing, signal amplification, and logic operation within a single device, yet fundamentally suffering from an inherent gain-speed trade-off. Here, we demonstrate a 2D photovoltaic phototransistor that overcomes this limitation using a MoS2/PtSe2 heterojunction to gate a
graphene channel. The ultrafast photovoltaic effect in the heterojunction enables charge separation, yielding ultrahigh photoconductive gain (up to 10^8) in
graphene channel via interfacial gating. Besides, the response time (below the instrumental resolution of 550 ns) is governed by carrier transit in
graphene channel, enabling simultaneous high speed and high gain. Moreover, broadband photodetection from visible to near-infrared is enabled by the optical properties of the MoS2/PtSe2 heterojunction, with the detectivity exceeding 10^11 Jones. These results establish a new paradigm for high-performance 2D phototransistors by harnessing photovoltaic and photogating effects to overcome the classical gain-speed trade-off.
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All authors Yihan Yin, Jiayi Zhang, Xiaolong Zhang, Jiongtao Zhang, Liang Liu, Haiya Ma, Xiaoguang Luo, Xuetao Gan
Materials Science
Conditional grain-graph diffusion for property-guided inverse design of polycrystalline microstructures
Yuheng Zhou, Xiao Shang, Huicong Chen et al. (+1 more)
Graph representations compactly encode polycrystalline microstructures while retaining grain
topology and grain boundary information. We present a conditional graph
diffusion framework for property-guided inverse design of dual-phase Ti-6Al-4V microstructures. An enhanced grain graph neural network (GNN) with grain boundary edge features, learnable node and edge
embeddings, and multi-statistic pooling serves as a forward surrogate for stress prediction and candidate evaluation. The conditional
diffusion model generates candidates through reverse
diffusion under prescribed {\alpha}-phase volume fraction, elastic modulus, and yield-stress proxy targets. Across four target regimes and independently seeded starting sets, generated candidates consistently approach the prescribed properties, including a target outside the property envelope of the existing microstructures. Local crystallographic consistency is evaluated post-generation from deviations from the Burgers orientation relationship (BOR). BOR-aware ranking increases mean BOR consistency by up to 44.9% and 56.4% for the in- and out-of-envelope targets, respectively, while maintaining property
alignment. Finite element validation of the five best candidates in each primary design case yields a maximum absolute relative error of 1.0% in their mean properties. In a representative
benchmark,
diffusion requires 32 candidate evaluations per input graph, compared with approximately 40,000 for random search and evolutionary optimization, and reduces runtime by approximately two orders of magnitude in the tested implementations. These results establish conditional grain-graph
diffusion as an efficient framework for property-guided polycrystalline microstructure design.
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All authors Yuheng Zhou, Xiao Shang, Huicong Chen, Yu Zou
Materials Science
Reconstruction-Dependent Imaging, Reactivity and Local Reduction of the CeO$_2$(100) surface
Kyungmin Kim, Manuel González Lastre, Estefanía Fernández-Villanueva et al. (+7 more)
The possibility of mapping the local reactivity and reduction state to the atomic structure of chemically active oxide surfaces opens new avenues for further understanding of catalysis. Here, we combine scanning tunnelling (STM) and atomic force microscopy (AFM) with first-principles modelling to explore this possibility on the CeO2(100) surface. While STM reveals the periodicity of cerium-terminated and oxygen-terminated CeO$_2$(100) reconstructions coexisting on the same surface, AFM imaging and force spectroscopy provide direct identification of the exposed atomic species and their reactivity as the chemical interaction with the probe. Density functional theory based STM and AFM simulations reproduce the main experimental observations and show that STM contrast cannot be in general assigned to the atomic positions of certain chemical species, as traditionally assumed from previous studies. Simulated STM contrast of the two reconstructions across different reduction states associated with the removal of oxygen atoms in deeper layers, evidence that STM alone does not offer a robust fingerprint of the local reduction state for the cerium-terminated reconstruction, but it is sensitive to the reduced state in the case of the oxygen-terminated one, being able to provide information on a mixed distribution of Ce$^{3+}$ and Ce$^{4+}$ ions on the first sub-surface Ce layer.
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All authors Kyungmin Kim, Manuel González Lastre, Estefanía Fernández-Villanueva, Pablo Pou, Hossein Sepehri-Amin, Masayuki Abe, Shigeki Kawai, M. Verónica Ganduglia-Pirovano, Ruben Perez, Oscar Custance
Materials Science
Ultrahigh Intrinsic Hole Mobilities in $M$N$_2$ ($M$= Mo and W) at Room Temperature
Zhongjuan Han, Rong-Tian Pang, Wu Xiong et al. (+3 more)
High-mobility $p$-type
semiconductors are essential for advanced electronic devices but remain scarce. Here, using a hierarchical screening framework that combines first-principles calculations with Boltzmann transport theory, we identify $M$N$_2$ ($M$= Mo and W) family as polar
semiconductors with exceptionally high intrinsic hole mobilities. In particular, 1H-WN$_2$ exhibits a room-temperature hole mobility exceeding $10^{4}$~$\mathrm{cm^2\,V^{-1}\,s^{-1}}$. This exceptional transport performance arises from the synergistic suppression of polar-optical-
phonon and acoustic-
phonon scattering, together with a reduced intervalley-scattering phase space induced by
spin–valley locking. These effects arise from anomalously small Born effective charges, strong covalent N–N bonds, and orbital hybridization between N-$2p_x$/$2p_y$ and W-$5d_{xy}$/$5d_{x^2-y^2}$ in the N$_2$-dimer-based structure. Our results establish MoN$_2$ and WN$_2$ as a promising class of high-mobility polar
semiconductors and introduce a
crystal-structure-based strategy for concurrently suppressing multiple electron–
phonon scattering channels, thereby revising design principles for high-mobility materials.
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All authors Zhongjuan Han, Rong-Tian Pang, Wu Xiong, Zhonghao Xia, Jin-Jian Zhou, Jiangang He
Materials Science · Cross-listed from cond-mat.mes-hall
Spin selectivity induced by non-collinear spins in Rashba wires
Luciano Jacopo D'Onofrio, Maria Teresa Mercaldo, Mario Cuoco et al. (+1 more)
We report a previously overlooked general mechanism to obtain highly efficient
spin selectivity in conventional time-reversal symmetric one-dimensional systems without invoking phase decoherence. We reveal that Rashba
quantum wires featuring non-collinear
spin states at the Fermi level inherently possess
spin-selective transport properties. We show that this
spin noncollinearity can be systematically designed and engineered by introducing an additional pseudospin degree of freedom - such as valley, sublattice, or orbital angular momentum - into
spin-orbit coupled systems. By applying this framework to multi-subband semiconducting
quantum wires and oxide nanowires, we establish a generalized route toward
quantum-coherent
spin selectivity up to 10 %. Our findings offer practical design principles for
spin-selective transport devices.
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All authors Luciano Jacopo D'Onofrio, Maria Teresa Mercaldo, Mario Cuoco, Carmine Ortix
Materials Science
Uncertainty-guided active learning for surrogate prediction of stream-finishing wear fields
Anand Kumar, Puli Saikiran, Vineet Dawara et al. (+1 more)
In stream finishing, the wear experienced by a workpiece depends strongly on its orientation within the rotating abrasive media. Determining suitable orientations to achieve uniform wear requires evaluating the wear-rate field over all feasible orientations. Although the discrete element method (DEM) accurately resolves particle interactions, simulating hundreds of feasible orientations for a new geometry is computationally expensive. We present an uncertainty-guided surrogate framework that predicts, directly from geometry, the three fields governing erosion: per-triangle normal impact velocity, tangential impact velocity, and particle impact flux. These fields are combined through the Finnie wear model to reconstruct the wear-rate distribution. The surrogate employs a deep ensemble whose disagreement estimates epistemic uncertainty, enabling an active-learning strategy that selectively performs DEM simulations for the most uncertain orientations. Trained using only $13\%$ of the $696$ feasible orientations, the surrogate achieves Spearman rank correlations of $0.93$, $0.89$, and $0.93$ for the normal impact velocity, tangential impact velocity, and particle impact flux, respectively. Moreover, the predicted uncertainty is well calibrated, reliably anticipating prediction error and the fidelity of the reconstructed wear field, which matches DEM with a Spearman rank correlation of up to $0.97$ for low-uncertainty orientations and degrades in a controlled manner as uncertainty increases.
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All authors Anand Kumar, Puli Saikiran, Vineet Dawara, Koushik Viswanathan
Materials Science
Spin- and Angle-resolved Photoelectron Spectroscopy Study of the Quantum Spin Hall Insulator Bismuthene and its Precursor Phase
Niclas Tilgner, Andres David Peña Unigarro, Susanne Wolff et al. (+6 more)
Recent studies have revealed that a confined bismuth layer at the
graphene/SiC interface can be reversibly switched between a topologically trivial precursor phase and the
quantum spin Hall
insulator bismuthene. Here, we present a detailed
spin- and angle-resolved photoelectron spectroscopy study of both structures, resolving the
spin texture of their low-energy electronic states. Owing to the strong intrinsic
spin-orbit coupling of bismuth and the asymmetric confinement potential at the interface, the valence bands of both structures are Rashba-split. We demonstrate the expected
spin-momentum locking for both phases and Kramers' doublets through the investigation of the valence bands'
spin polarization at multiple positions in reciprocal space.
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All authors Niclas Tilgner, Andres David Peña Unigarro, Susanne Wolff, Mats Leandersson, Craig Polley, Fabian Göhler, Sibylle Gemming, Thomas Seyller, Philip Schädlich
Materials Science
Machine-Learning-Compatible CALPHAD-type Optimization from Phase Equilibria by Auto-differentiation
Wenhao Zhang, Jean-Claude Crivello, Yusuke Matsuoka et al. (+2 more)
To accurately determine phase boundaries and phase transitions, thermodynamic models that describe phase free energies often have to be optimized based on experimentally observed phase
equilibria. While different approaches exist for thermodynamic optimization, they are often implemented in ways that are not compatible with machine learning workflows requiring differentiable calculation of the loss function. In this work, we derive a phase-
equilibrium loss function based on thermodynamic potentials that can be efficiently evaluated and enables gradient-based optimization by auto-differentiation in the PyTorch package. By minimizing this loss function, general thermodynamic model parameters can be optimized with respect to experimental phase-
equilibria data. Using thermodynamic models in the CALculation of PHAse Diagram (CALPHAD) framework, we illustrate successful and efficient optimization in different systems, including ternary systems with more than 100 parameters. As the loss function is defined independently of the details of the thermodynamic models, it can be used to optimize machine learning thermodynamic models in general. In particular, we demonstrate top-down optimization of an atomistic potential from target phase
equilibria.
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All authors Wenhao Zhang, Jean-Claude Crivello, Yusuke Matsuoka, Toshiyuki Koyama, Taichi Abe
Materials Science · Cross-listed from cond-mat.supr-con
Ab initio prediction of $d_{x^2-y^2}$-wave superconductivity in infinite-layer nickelates
Guang-Yu Guo, Ren-Guo Guo, Yun-Chen Liao et al. (+1 more)
Infinite-layer nickelates have recently emerged as a new family of potential unconventional high critical temperature ($T_c$)
superconductors. However, fundamental questions such as their superconducting (SC) pairing mechanism and gap
symmetry remain under intense debate. Here we present a fully ab initio theoretical study on the SC properties of optimally doped nickelates $Re$$_{0.8}$Sr$_{0.2}$NiO$_2$ ($Re=$ La, Pr, Nd), based on the density functional theory for
superconductors calculations with electron-
phonon coupling (EPC), screened Coulomb repulsion and
spin fluctuation (SF) interaction treated on an equal footing. We find that $Re_{0.8}$Sr$_{0.2}$NiO$_2$ are two-band
superconductors with sign reversal $d_{x^2-y^2}(\pm)$-wave gap functions on the different Fermi surface (FS) pockets. Interestingly, when the SF interaction is turned off, $T_c$ becomes negligibly small ($\sim$0.01 K), thus demonstrating that the superconductivity in $Re_{0.8}$Sr$_{0.2}$NiO$_2$ is driven by SF interaction. Moreover, our ab initio calculations reveal that the SF interaction is an order of magnitude stronger than both EPC and Coulomb repulsion on the large quasi-two-dimensional FS pocket around the Brillouin zone (BZ) center, thus leading to the SF-mediated pairing mechanism, although the EPC dominates on the small three-dimensional electron FS pockets at the BZ corners. The emergence of nodal $d_{x^2-y^2}(\pm)$-wave gap structure is traced to the pronounced peaks in the Lindhard response function at the BZ corners. Our calculated FS, SC critical temperature, nodal gap structure and SC quasiparticle density of states are consistent with most available experiments. Furthermore, predicted unconventional SC properties such as scanning tunneling spectra of La$_{0.8}$Sr$_{0.2}$NiO$_2$ and Pr$_{0.8}$Sr$_{0.2}$NiO$_2$ are ready for immediate experimental verifications.
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All authors Guang-Yu Guo, Ren-Guo Guo, Yun-Chen Liao, Yang-hao Chan
Materials Science · Cross-listed from cond-mat.mes-hall
Correlated Insulator Moiré Bolometer
L. Elesin, A. L. Shilov, M. Kravtsov et al. (+14 more)
Light incident on an
insulator is generally not expected to turn it into a metal without invoking intense ultrafast excitation that leads to transient structural transitions. Here we show that magic-angle twisted bilayer
graphene tuned to half filling of the moiré band provides a notable exception to this expectation. We find that weak beam of long-wavelength
photons, with energies comparable to the flat-band width, selectively heat the low-heat-capacity electronic subsystem, thereby suppressing the correlated gap. This produces a giant resistance change governed not by a persistent photocarrier population, but by the extreme sensitivity of a many-body correlated gap to weak electronic heating. The resulting
photon-driven
insulator-to-metal transition produces a broadband low-noise photoresponse with voltage responsivity exceeding millivolts per nW of absorbed power. The mechanism is dual to superconducting hot-electron response: radiation-heated electrons suppress a many-body order, but in reverse the correlated
insulator melts into a metal, providing robustness to
magnetic fields of several tesla and a sharp
insulator-to-metal resistive contrast. Our results establish correlated flat-band systems as a platform for ultra-sensitive detection of faint long-wavelength radiation.
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All authors L. Elesin, A. L. Shilov, M. Kravtsov, X. Zhou, M. Lukianov, A. Kuksov, S. Jana, I. Iorsh, R. Izmaylov, K. Shein, I. Gayduchenko, T. Taniguchi, K. Watanabe, K. S. Novoselov, G. N. Goltsman, A. Principi, D. A. Bandurin
Materials Science · Cross-listed from cond-mat.str-el
Negative thermal expansion, lattice dynamics, and complex magnetism in TbFeO$_3$
Shubham Farswan, Reshma Kumawat, Dipankar Sarkar et al. (+4 more)
We report a temperature-dependent investigation of orthoferrite TbFeO$_3$ using x-ray diffraction, DC magnetization, and Raman scattering, complemented by room-temperature x-ray photoelectron spectroscopy. X-ray diffraction reveals negative thermal expansion over 5-300 K, with a small but systematic increase in unit-
cell volume upon cooling in the absence of any structural phase transition. Raman scattering measurements identify the Raman-active
phonon modes and show clear deviations from the conventional Klemens anharmonic decay model, particularly in
phonon frequencies, indicating the presence of
spin-
phonon coupling. Two modes of $A_g$ and $B_{1g}$
symmetry exhibit a crossover from Gaussian-dominated line shapes at low temperatures to mixed Gaussian-Lorentzian profiles at higher temperatures, reflecting a transition from inhomogeneous broadening to lifetime-driven dynamics. High-energy Raman spectra reveal two-
magnon excitations associated with the Fe sublattice, consistent with linear
spin-wave theory, whose spectral weight shows only weak temperature dependence. In addition, a broad Raman mode emerging below $\sim 175$ K exhibits an order-parameter-like temperature
evolution and coincides with the onset of
phonon anomalies, while no corresponding strong anomaly is observed in the two-
magnon response. Taken together, these results establish TbFeO$_3$ as a system with pronounced interplay among
lattice dynamics,
spin correlations, and emergent local
magnetic-
lattice anomalies.
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All authors Shubham Farswan, Reshma Kumawat, Dipankar Sarkar, Deeksha Singh, Md. Atif Hasan, Devajyoti Mukherjee, Kaushik Sen
Materials Science
The AFLOW Library of Crystallographic Prototypes: Part 5
Nicholas H. Anderson, Michael J. Mehl, Hagen Eckert et al. (+3 more)
The AFLOW library of crystallographic prototypes has been updated to incorporate an additional 344 entries, which now reaches 2,127 prototypes. ICSD and CCDC numbers have been added to the website alongside improvements to the user interface. New tutorials covering the basics of crystallography in the context of materials science have also been added. Lastly, we covered the current known applications of AFLOW prototype labels and materials data across research software.
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All authors Nicholas H. Anderson, Michael J. Mehl, Hagen Eckert, Simon Divilov, Xiomara Campilongo, Stefano Curtarolo
Materials Science
An essay on $d_0$ in neutron-based strain measurement techniques: equilibrium-based methods for non-destructive $d_0$ estimation
Christopher Wensrich, Giles Parkes, Vladimir Luzin et al. (+2 more)
Determination of the stress-free reference
lattice spacing, $d_0$, is a central and often underestimated difficulty in diffraction-based strain measurement. Although commonly treated as a material constant, $d_0$ often varies with position and measurement direction as a result of composition, phase, texture and residual stress at the sub-bulk scale. While direct measurement of $d_0$ from coupons is usually preferable, this is sometimes impractical or even impossible. This paper reviews the $d_0$ problem in general and develops a hierarchy of non-destructive alternatives based on mechanical
equilibrium. This ranges from established techniques based on force-balance, to the application of boundary conditions and finally an approach based on point-wise
equilibrium within a sample, implemented through eigenstrain analysis. In all cases, examples are provided in the form of real samples including an additively manufactured Inconel cube, ancient Roman bronze medical probes and an ancient bronze dagger of purported Persian origin. These latter examples demonstrate that
equilibrium can provide a practical physical constraint for estimating $d_0$ when destructive reference measurements are entirely inappropriate.
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All authors Christopher Wensrich, Giles Parkes, Vladimir Luzin, Benjamin Daly, Floriana Salvemini