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
Disordered Systems and Neural Networks
Spin Quantum Hall Effect: the Critical Exponents
Hrant Topchyan, Win Nuding, Andreas Klümper et al. (+1 more)
The
spin quantum Hall effect (SQHE) provides one of the few examples of an Anderson localization transition for which exact critical exponents are known, making it an important testing ground for theories of disordered topological systems and conformal field theory. The corresponding network model, obtained by replacing the random $U(1)$ phases of the Chalker–Coddington model with random $SU(2)$
matrices, belongs to
symmetry class C of the Altland–Zirnbauer classification and is believed to describe quasiparticle transport in two-dimensional disordered
superconductors with broken time-reversal
symmetry. In this work, we perform high-precision numerical calculations of the localization-length exponent ($\nu$) and the boundary critical exponent ($\mu$) for the SQHE network model using the recently developed $S$-
matrix approach to random networks.
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All authors Hrant Topchyan, Win Nuding, Andreas Klümper, Ara Sedrakyan
Mesoscale and Nanoscale Physics
Magnetoelastic control of quantum correlations and field sensitivity in a spin-1/2 Heisenberg dimer
E. W. B. de Souza, Moises Rojas and Onofre Rojas
We investigate the thermodynamic and
quantum properties of a magnetoelastic
spin-1/2 Heisenberg dimer, where the exchange interaction depends on the dimer displacement. By combining an exact treatment of the
spin sector with a harmonic description of the vibrational degree of freedom, we obtain an effective model in which each
spin configuration is associated with a distinct vibrational mode, leading to a non-factorizable partition function. We analyze the thermal behavior and identify regimes corresponding to entangled and fully polarized states.
Quantum correlations are analyzed through concurrence and local
quantum uncertainty, showing that while
entanglement is rapidly suppressed by temperature, nonclassical correlations persist over a broader range due to the competition between
spin sectors. We further examine the
magnetic Fisher information, which provides a measure of the sensitivity of the system to the external
magnetic field. Its behavior reveals enhanced response in crossover regions where magnetoelastic effects induce strong redistribution of the level populations. Our results demonstrate that magnetoelastic coupling plays a central role in controlling both
quantum correlations and
magnetic response, establishing a direct link between
entanglement, nonclassical correlations, and thermodynamic sensitivity in coupled
spin-dimer systems.
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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
Mesoscale and Nanoscale Physics
How NOT to build control-target gates in semiconductor quantum dots and beyond
Roman Korol, John Nichol and Ignacio Franco
Universal
quantum computation requires single-
qubit control together with at least one entangling two-
qubit gate. CNOT and CROT gates are two famous examples of such gates, wherein the state of one
qubit (control) dictates the transformation applied to the other (target). By using a simple derivation motivated by
symmetry, we show that current device architectures of
semiconductor-based
quantum dot devices prevent efficient implementation of a CNOT and other asymmetric control-target gates via Heisenberg exchange, Coulomb repulsion, or other interaction that is invariant under
spin exchange. Guided by this general principle, we propose a heterogeneous blueprint of double
quantum dot devices that enables efficient implementation of the CNOT by breaking the
spin exchange
symmetry. Crucially, our numerical simulations predict that this novel device blueprint can enable a single-pulse fault-tolerant 100-ns CNOT gate in isotopically purified silicon.
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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
Quantum Gases · Cross-listed from physics.optics
Solitons in optical couplers: introduction and perspectives
Boris A. Malomed
This minireview provides a brief summary and a discussion of directions for further development of theoretical and, chiefly, experimental studies of bright
solitons in optical couplers, i.e., dual-core waveguides which combine the linear inter-core coupling (tunneling of light between the parallel cores with the intra-core group-velocity dispersion and self-focusing Kerr (cubic) nonlinearity. Following a short introduction to the field, the article focuses on a brief review of relatively recent experimental results for the switching of
solitons in dual-core nonlinear optical fibers and the spontaneous emergence of stable asymmetric two-core
solitons in the couplers with the symmetric dual-core structure.
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Statistical Mechanics · Cross-listed from quant-ph
Work Statistics of Autonomous Quantum Energy Pumps
Yang Peng
We develop a terminal-resolved theory of work statistics for autonomous
quantum energy pumps. By modeling the systems that supply and receive energy as explicit
quantum terminals, the energy exchanged with each terminal is defined directly from its
Hamiltonian change. When the terminals are modeled by ideal clocks, these full-space observables admit exact representations on the pump
Hilbert space and recover the conventional phase-derivative currents of periodically and quasiperiodically driven systems. The framework resolves transported work from energy accumulated in the pump. It also incorporates arbitrary initial pump–terminal correlations and identifies when correlations can enhance directional energy transfer under uncertain driving phases. For periodic pumps, we derive finite-cycle work statistics in Floquet eigenstates, relate their fluctuations to Floquet
quantum geometry, and show that the long-time terminal currents become mutually compatible. An exactly solvable two-terminal
qubit exhibits noise matching, in which transport becomes sharp through cancellation of common-mode terminal fluctuations even though the individual terminal energies remain noisy. Finally, for physical terminals beyond the ideal-clock limit, we introduce a positive work-variance gap that quantifies the fluctuations missed by a pump-only description. A coherent-cavity
benchmark shows systematic convergence toward the ideal-clock regime with increasing occupation while demonstrating that agreement of the mean current alone does not guarantee accurate work statistics.
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Mesoscale and Nanoscale Physics
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
Soft Condensed Matter
Confinement-Induced Optimization of Fluctuation-Induced Forces in Active Fluids
Reza Shaebani, Hashem Fatemi, Hamidreza Khalilian et al. (+1 more)
Active matter generates nonequilibrium fluctuations that mediate effective interactions between immersed objects. While fluctuation-induced (FI) forces in active fluids depend on activity, density, and geometry, their dependence on confinement remains poorly understood. We study FI forces between fixed intruders in two-dimensional active fluids composed of self-propelled circular or rodlike particles using Langevin dynamics simulations. We find that the FI force exhibits a pronounced nonmonotonic dependence on intruder separation, reaching a maximum at an optimal gap size well beyond the depletion regime, in contrast to the commonly assumed monotonic decay. This optimal confinement is robust across parameters and is more pronounced for elongated particles. The effect arises from a confinement-controlled balance between particle transport and crowding: narrow gaps hinder exchange between inner and outer regions, whereas large separations effectively decouple the intruders. At intermediate distances, enhanced crowding around the intruders generates maximal collision-rate asymmetries, leading to the strongest effective interactions. These results identify confinement geometry as a key control parameter for FI forces in active matter.
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All authors Reza Shaebani, Hashem Fatemi, Hamidreza Khalilian, Jalal Sarabadani
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
Statistical Mechanics · Cross-listed from nlin.PS
Duck hunting with quantum mechanics
Artem Alexandrov
We bridge two sides of singular perturbation theory: the classical theory of slow-fast systems and the semi-classical approach to
quantum mechanical systems. For a specific but physically important class of dynamical systems, we show that purely classical and exotic objects, so-called canard solutions, are shadows of instantons in the corresponding
quantum system. We demonstrate that canard solutions exist in a domain of parameter space whose boundaries are determined by an instanton action. We illustrate our statements analytically for the relevant example, the overdamped Josephson junction, and confirm them numerically. For the Josephson junction, the canard window is the exponentially narrow gap between consecutive Shapiro steps.
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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
Superconductivity
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
Mesoscale and Nanoscale Physics
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
Strongly Correlated Electrons
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
Strongly Correlated Electrons
Breakdown of Universal Whirling Order in a Heisenberg Tsai-Type Approximant
Farid Labib, Guillaume Beutier, Alessandro Bombardi et al. (+2 more)
Noncoplanar whirling
magnetic order has recently been proposed as a universal
magnetic state in non-Heisenberg Tsai-type quasicrystal approximants. Here, X-ray resonant
magnetic scattering measurements on Heisenberg and non-Heisenberg Au-Al-R (R = Gd, Tb) 1/1 approximants reveal a clear breakdown of this universality in the Heisenberg limit. While the non-Heisenberg Au-Al-Tb system is well described by the previously identified whirling
magnetic structure, the Heisenberg Au-Al-Gd counterpart exhibits qualitatively different azimuthal-angle dependences that are incompatible with the universal whirling-order model. Despite nearly identical
crystal structures and comparable
magnetic energy scales, the two systems stabilize distinct
antiferromagnetic ground states with the same propagation vector k = (1, 0, 0), demonstrating that the apparent universality of whirling order is not a consequence of Tsai-cluster geometry alone but requires
spin anisotropy. These results further reveal the emergence of a competing
manifold of nearly degenerate
magnetic states in the Heisenberg limit.
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All authors Farid Labib, Guillaume Beutier, Alessandro Bombardi, Marc de Boissieu, Ryuji Tamura
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
Mesoscale and Nanoscale Physics
Skyrmion Excitations in the $\nu=-1$ Quantum Hall state in Monolayer Graphene
Jincheng An, Ajit C. Balram and Ganpathy Murthy
We investigate the skyrmion excited states atop the $SU(4)$
quantum Hall ferromagnetic ground state at filling factor $\nu=-1$ in monolayer
graphene. The competition among short-range anisotropic interactions, the Zeeman coupling, and sublattice
symmetry-breaking potential gives rise to four distinct
spin-valley-ordered ground-state phases. Combining effective field theory with the Hartree–Fock approximation, we develop a variational framework that incorporates both the long-range Coulomb interaction and the
symmetry-breaking terms on an equal footing. Variational minimization determines the optimal skyrmion texture, including both its spatial radial profile and internal $SU(4)$ spinor structure. We establish the phase diagram of skyrmion excitations, identify thirteen distinct skyrmion phases under different external-field conditions, and determine their
spin-valley textures, energies, and characteristic sizes. The robustness of the results against different radial ansätze demonstrates the reliability of our variational approach. Our work provides a systematic framework for studying skyrmion excitations in multicomponent
quantum Hall ferromagnets and can be naturally extended to more general $SU(4)$
quantum Hall systems.
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Mesoscale and Nanoscale Physics
Planar Interfaces for Transmission of Chiral Spin Textures
Robin Msiska, Cynthia J.O. Reichhardt, Charles Reichhardt et al. (+2 more)
Lateral
magnetic interfaces provide a direct way to test whether skyrmions remain robust when driven across abrupt changes in material parameters and
magnetic order. Here we study skyrmion transmission across planar ferromagnet-ferromagnet (FM-FM), antiferromagnet-antiferromagnet (AFM-AFM), ferromagnet-antiferromagnet (FM-AFM), and antiferromagnet-ferromagnet (AFM-FM) interfaces using micromagnetic simulations and analytic reduced-coordinate criteria. The outcomes are organized into phase diagrams according to the morphology formed in the receiving region, distinguishing compact transmission from deformed skyrmions, stripe-domain states, amorphous textures, and relaxation into the background. Same-order FM-FM and AFM-AFM skyrmion transmission is captured by an analytically defined range of the reduced Dzyaloshinskii-Moriya interaction, identifying the wall-softening regime that supports compact transmission without stripe formation. Mixed-order FM-AFM and AFM-FM interfaces are directionally distinct, requiring conversion between
ferromagnetic magnetization and
antiferromagnetic Néel textures. These results show that planar interfaces act as active transport elements and provide reduced design criteria for heterogeneous skyrmion tracks.
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All authors Robin Msiska, Cynthia J.O. Reichhardt, Charles Reichhardt, Eric Fullerton, Avadh Saxena
Mesoscale and Nanoscale Physics
Universal scaling of the Anomalous Hall voltage of magnetic layer with the adjacent conducting layer
Zhihao Yan, Qianbiao Liu, Zhengxiao Li et al. (+1 more)
The anomalous
Hall voltage of
magnetic heterostructures plays a key role as the indicator for the magnetization state and its interplay with a variety of spintronic effects. In this letter, we report the observation, mechanism, and impact of the universal, dramatic scaling of the anomalous
Hall voltage of
magnetic heterostructures with the thickness and resistivity of the nonmagnetic conducting layers (e.g., normal metal) by combining transport experiments, analytical derivation, and finite-element analyses. We identify that the mechanism is the serial resistor effect of the
magnetic and non-
magnetic layers within the
magnetic heterostructures and irrelevant to any
Fermi surface variation or angular momentum injection from the nonmagnetic layer to the
magnetic layer. We also show that the accuracy of the harmonic
Hall voltage analyses of
magnetic heterostructures are unaffected by the under-measuring of the anomalous
Hall voltage and other transverse voltages due to the serial resistor effect. These findings provide crucial information for understanding a variety of spintronic phenomena involving the anomalous
Hall and other transverse voltages.
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All authors Zhihao Yan, Qianbiao Liu, Zhengxiao Li, Lijun Zhu
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