Strongly Correlated Electrons
Stabilization of $\alpha$-UH$_3$ in U-Hf Hydrides: Structural, Magnetic, Thermodynamic, and Transport Properties
Shanmukh Veera Venkata Uday Kumar Devanaboina, Oleksandra Koloskova, Silvie Maskova-Cerna et al. (+1 more)
Hf substitution stabilizes the metastable body-centered cubic (bcc) $\alpha$-UH$3$ phase in uranium hydrides, enabling systematic measurements of its
magnetic, thermodynamic, and transport properties. (UH$3$)${1-x}$Hf$x$ hydrides ($x = 0.10, 0.15, 0.30, 0.40$) were obtained by hydrogenation of U${1-x}$Hf$x$ precursor
alloys. Powder X-ray diffraction shows a progressive suppression of $\beta$-UH$3$ phase with increasing $x$, with $\alpha$-UH$3$ domination at $x = 0.30$ and $\beta$-UH$3$ nearly fully suppressed at $x = 0.40$. Magnetization measurements show
ferromagnetic behavior for all compositions with Curie temperatures in the range $T\mathrm{C} \approx 178$–$185$ K and a maximum near $x = 0.15$; however, the spontaneous magnetization is strongly reduced with Hf content, decreasing from $1.0,\mu\mathrm{B}$/U in pure $\beta$-UH$3$ to $0.46,\mu\mathrm{B}$/U for (UH$3$)${0.60}$Hf${0.40}$. Specific-heat data show a broadened Curie anomaly in the $\alpha$-UH$3$ rich hydride samples, consistent with a distribution of $T\mathrm{C}$ values arising from
ferromagnetic inhomogeneities. Specific heat also reveals a monotonic decrease in the Sommerfeld coefficient with increasing Hf concentration, reflecting a reduction in the electronic density of states at the
Fermi level, especially in (UH$3$)${0.60}$Hf${0.40}$. The resistivity of (UH$3$)${0.60}$Hf${0.40}$ is very large, exhibits a robust negative temperature coefficient over 2–300 K, and shows only weak magnetoresistance, placing transport in a strongly incoherent, disorder-dominated regime.
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All authors Shanmukh Veera Venkata Uday Kumar Devanaboina, Oleksandra Koloskova, Silvie Maskova-Cerna, Ladislav Havela
Strongly Correlated Electrons
Exceptional nodal rings emerging in spinful Rice-Mele chains
E. S. Ma and Z. Song
The Weyl exceptional nodal lines usually occur in 3D topological semimetals, but also emerge in the parameter space of 1D systems. In this work, we study the impact of dissipation on the nodal ring in a 3D topological semimetal. We find that the energy spectrum becomes fully complex in the presence of dissipation, and the original nodal ring is split into two exceptional rings. We introduce a
vortex field in the momentum space, which is generated from the spectrum, to characterize the
topology of the exceptional rings. This provides a clear physical picture of the topological structure. The two exceptional rings act as two
vortex filaments of a free
vortex flow with opposite circulations. In this context, the 3D topological semimetal is the boundary separating two
quantum phases identified by two configurations of exceptional rings. We also propose a 1D model that has the same topological feature in the parameter space. It provides a simple way to measure the topological invariant in a low-dimensional system. Numerical simulations indicate that the topological invariant is robust under the random perturbations of the system parameters.
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Materials Science
MoireStudio: A Universal Twisted Electronic Structure Calculation Package
Junxi Yu, Yichen Liu and Cheng-Cheng Liu
Twistronics is an emerging and captivating field in condensed matter physics and material science. However, accurately and efficiently calculating the electronic structures of twisted systems remains a significant challenge. To address this, we have developed MoireStudio, a universal Python-based computational package for twisted electronic structures. Its functionalities include commensurate structure search, structure generation, parameterization, and construction for tight-binding models and continuum models, and the precise incorporation of full relaxation effects. The package is applicable to arbitrary combinations of two-dimensional materials, including rectangular
lattices and
heterostructures. User-friendly and easy to use, MoireStudio supports parallel large-scale computations, provides visualization capabilities, and offers interfaces with third-party software. It is poised to become a convenient and powerful tool for researchers in twistronics fields.
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Mesoscale and Nanoscale Physics
High-Harmonic Spin and Charge Pumping in Altermagnets
Ousmane Ly
We report the emergence of highly nonlinear
spin and charge pumping in an altermagnetic system driven by
magnetic dynamics. The non-relativistic
spin-momentum coupling inherent to altermagnets (AMs) generates a
giant momentum dependent
spin splitting, leading to strong
spin-flip scattering in the presence of a precessing
magnetic order driving the altermagnetic system out of
equilibrium. Our simulations reveal the emission of hundreds of harmonics under realistic conditions, with amplitudes far exceeding those obtained in light-driven schemes. Notably, in contrast to
ferromagnetic and conventional
antiferromagnetic systems, where nonlinear emission typically requires additional
spin-orbit coupling, AMs intrinsically support high-harmonic
spin and charge pumping. These results identify altermagnetic systems as a promising platform for efficient THz emitters and highly nonlinear spintronic devices.
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Materials Science
How Geometry Tames Disorder in Lattice Fracture
Matthaios Chouzouris, Leo de Waal, Antoine Sanner et al. (+3 more)
We investigate the fracture behavior of pre-cracked triangular beam-
lattices whose elements have failure stresses drawn from a Weibull distribution. Through a statistical analysis and numerical simulations, we identify and verify the existence of three distinct failure regimes: (i) disorder is effectively suppressed, (ii) disorder manifests locally near the crack tip, modifying the crack morphology, and (iii) disorder manifests globally, leading to initially diffuse failure. Our model naturally reveals the key parameters governing this behavior: the Weibull modulus, quantifying the spread in failure thresholds, and a
geometric quantity termed the Slenderness Ratio. We also reproduce the disorder-induced toughening reported in previous experimental and numerical studies, further demonstrating that its manifestation depends non-monotonically on disorder. Crucially, our results indicate that this toughening cannot be simply connected to the amount of damage in the
lattice, challenging interpretations that attribute increased fracture energy solely to enhanced crack tortuosity or diffuse failure. Overall, our results establish geometry as a powerful control parameter for regulating how disorder is expressed during fracture in beam-
lattices, with broader implications for the disorder-induced toughening in engineered materials.
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All authors Matthaios Chouzouris, Leo de Waal, Antoine Sanner, Alessandra Lingua, David S. Kammer, Marcelo A. Dias
Materials Science
Pressure dependent topological, superconducting, optoelectronic and thermophysical properties of Ta2Se chalcogenide: Theoretical insights
Tauhidur Rahman, Jubair Hossan Abir, Sourav Kumar Sutradhar et al. (+4 more)
Tetragonal Ta2Se is a layered, Ta-rich chalcogenide that departs from conventional MX2 transition-metal dichalcogenides by hosting dense Ta-Ta networks capped by Se square-net layers. Here, we present a unified first-principles investigation of hydrostatic-pressure tuning in Ta2Se from 0 to 10 GPa, connecting the structural response, mechanical stability, thermophysical indicators, bonding
evolution, electronic and optical behavior,
lattice dynamics and superconductivity within a single framework. The derived thermophysical descriptors corroborate a pressure-stiffened
lattice: density increases, Debye temperature rises, melting temperature is elevated and minimum thermal conductivity increases, whereas the Grüneisen parameter remains within a narrow window, suggesting no anomalous anharmonic softening. Bond population metrics and electron-density-difference analysis revealed a mixed metallic-covalent bonding picture dominated by a robust Ta-Ta metallic backbone, accompanied by pressure-strengthened Ta-Se hybridization. Electronic-structure calculations show persistent
metallicity under compression; pressure broadens bands, reduces density of states at the
Fermi level, reshapes the
Fermi surface and points to a possible Lifshitz-type reconstruction without
symmetry breaking. The optical response remained metallic with Drude-like low-energy behavior and pressure-tunable spectral features. The
phonon dispersions exhibit no imaginary modes, confirming dynamical stability. Electron-
phonon coupling calculations classify Ta2Se as a weak-coupling,
phonon-mediated
superconductor with Tc around 3.9 K, consistent with available experiments and establish pressure as a practical control knob for stability and superconductivity-relevant descriptors in this metal-rich layered platform.
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All authors Tauhidur Rahman, Jubair Hossan Abir, Sourav Kumar Sutradhar, Sraboni Saha Moly, Mst. Maskura Khatun, Md. Asif Afzal, Saleh Hasan Naqib
Disordered Systems and Neural Networks · Cross-listed from physics.soc-ph
Topology and higher-order global synchronization on directed and hollow simplicial and cell complexes
Runyue Wang, Timoteo Carletti and Ginestra Bianconi
Higher-order networks encode the many-body interactions of complex systems ranging from the
brain to biological transportation networks. Simplicial and
cell complexes are ideal higher-order network representations for investigating higher-order topological dynamics where dynamical variables are not only associated with nodes, but also with edges, triangles, and higher-order simplices and
cells. Global Topological Synchronization (GTS) refers to the dynamical state in which identical oscillators associated with higher-dimensional simplices and
cells oscillate in unison. On standard unweighted and undirected complexes this dynamical state can be achieved only under strict topological and combinatorial conditions on the underlying discrete support. In this work we consider generalized higher-order network representations including directed and hollow complexes. Based on an in depth investigation of their
topology defined by their associated algebraic
topology operators and Betti numbers, we determine under which conditions GTS can be observed. We show that directed complexes always admit a global topological synchronization state independently of their
topology and structure. However, we demonstrate that for directed complexes this dynamical state cannot be asymptotically stable. While hollow complexes require more stringent topological conditions to sustain global topological synchronization, these
topologies can favor both the existence and the stability of global topological synchronization with respect to undirected and unweighted complexes.
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Strongly Correlated Electrons
Raman Spectroscopic Investigation of Kitaev Quantum Spin Liquids
Vivek Kumar and Pradeep Kumar
Quantum spin liquids, a highly topologically entangled, dynamically correlated state where
quantum fluctuations preclude any long-range ordering down to absolute zero. In the search for a topologically robust
qubit, the scientific community has been in continuous hunt for real
quantum spin liquid systems. Alexei Kitaev in his exactly solvable model for a
spin-1/2 two-dimensional honeycomb
lattice, presented a system that hosts a topologically protected state (Majorana zero-modes). Under an applied external field, the Kitaev
spin liquids turn into a topologically non-trivial
chiral spin-
liquid state with non-abelian anionic excitations, which is crucial for
quantum computing. Earlier theoretical predictions advocated that Kitaev physics can be realized in
spin-orbit-coupled Mott
insulators such as honeycomb irradiates and ruthenates. However, the experimental findings continuously challenge the theoretical aspects, indicating the presence of non-Kitaev interactions in real materials, where the dimensionality, disorder (vacancy), chemical composition, generalized
spin-S, and external perturbations (pressure,
magnetic field, temperature) can actively tune the Kitaev interactions and the ground state excitations. In this review article, a comprehensive discussion is included with an updated literature survey in the context of the potential of Raman spectroscopy as a probe for Kitaev
quantum spin liquids.
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Materials Science
Microstructural origin of the simultaneous enhancements in strength and ductility of a nitrogen-doped high-entropy alloy
Xiaoxiang Wu, Zhujun Sun, Wenqi Guo et al. (+9 more)
As one of the most abundant interstitial elements, nitrogen (N) is effective in improving yield strength of metallic materials, due to interstitial solid solution strengthening. Doping N can substantially enhance the yield strength but often leads to a decreased ductility, revealing a strength-ductility trade-off phenomenon. Here, we simultaneously enhance the strength and ductility in a non-equiatomic CrMnFeCoNi high-
entropy alloy via N alloying and unravel the underlying microscopic mechanisms. The N-doped
alloy (1 at.% N) shows an excellent combination of higher yield strength (104% increase) and larger ductility (38% increase), with a two-stage strain hardening behavior, compared to the N-free
alloy. Detailed transmission electron microscopy (TEM) analysis reveals that N-doping introduces short-range order (SRO) domains within the microstructure, leads to pronounced planar slip, and promotes the formation of nano-spaced (6-15 nm) stacking faults and deformation twins. Continuous generation and interaction of the fine-spaced SFs act as a strong barrier for dislocation movement and provide ample room for dislocation storage. The interaction of SRO with dislocations and the
evolution of SFs ascribe to the first strain hardening stage, and the disordering of the SRO along with the activation of deformation twins are attributed to the second strain hardening stage. Our work shows that N-doping is effective in simultaneously improving the strength-ductility synergy and provides novel insights into
alloy design with slightly elevating the SFE, and manipulating the ordered structure within the HEA.
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All authors Xiaoxiang Wu, Zhujun Sun, Wenqi Guo, Chang Liu, Yong-Qiang Yan, Yan-Ning Zhang, Yuji Ikeda, Fritz Körmann, Jörg Neugebauer, Zhiming Li, Baptiste Gault, Ge Wu
Materials Science
High Photovoltaic Efficiency in Bulk-Stacked One-Dimensional GeSe$_{2}$ van der Waals Crystal
Seoung-Hun Kang, Youngjae Kim, Bo Gyu Jang et al. (+1 more)
Germanium diselenide (GeSe$_{2}$) has recently attracted substantial interest as a rare example of one-dimensional (1D) van der Waals material. Here, we investigate the photovoltaic potential of bulk-stacked GeSe$_{2}$ chains using first-principles calculations within the $GW0$ approximation and the Bethe-Salpeter equation (BSE) to capture quasiparticle and excitonic effects. The bulk GeSe$_{2}$ exhibits indirect GW band gaps of 1.92 eV (type-I) and 1.08 eV (type-II). Optical calculations show markedly stronger visible-light absorption in type-II, yielding a spectroscopically limited maximum efficiency (SLME) of ~25.6% at a 0.5 $\mu$m thickness.
Phonon and room-temperature ab initio molecular dynamics analyses indicate that type-II is dynamically stable, whereas type-I shows imaginary
phonon modes, suggesting a propensity for structural distortion. These results identify type-II GeSe2 as a promising stable absorber for thin-film photovoltaics with enhanced flexibility compared to typical 2D vdW systems.
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All authors Seoung-Hun Kang, Youngjae Kim, Bo Gyu Jang, Sejoong Kim
Quantum Gases
Toroidal Confinement and Beyond: Vorticity-Defined Morphologies of Dipolar $^{164}$Dy Quantum Droplets
S. Sanjay, S. Saravana Veni and Boris A. Malomed
We investigate the formation, stability, and dynamics of 3D ring-shaped and multipole vortical
quantum droplets (QDs) in non-rotating dipolar Bose-Einstein condensates held in a toroidal trapping potential. The QD dynamics are investigated in the framework of the extended Gross-Pitaevskii equation, which includes long-range dipole-dipole interactions (DDI) and the beyond-mean-field Lee-Huang-Yang (LHY) term, revealing the emergence of self-bound states. Stable stationary solutions for multipole QDs with different values of the topological charge (vorticity $S$) are shaped as necklace-like modes, with the number of \textquotedblleft beads" (multipole's order) $n=2S$, up to $S=6$. The stability area of the multipoles shrinks with the increase of $S$. For higher values of $S$ the centrifugal effect associated with the phase winding destabilizes the annular density and drives the formation of fragmented multipole droplet states. The dependence of the chemical potential, total energy and peak density on the norm (number of particles) and $S$ is produced. These findings uncover the stabilizing effect of the LHY correction and DDI anisotropy in maintaining complex QD states in the non-rotating configurations.
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Statistical Mechanics · Cross-listed from quant-ph
Tunable many-body burst in isolated quantum systems
Shozo Yamada, Akihiro Hokkyo and Masahito Ueda
Thermalization in isolated
quantum many-body systems can be nonmonotonic, with its process dependent on an initial state. We propose a numerical method to construct a low-entangled initial state that creates a "burst" – a transient deviation of an observable from its thermal
equilibrium value – at a designated time. We apply this method to demonstrate that a burst of magnetization can be realized for a nonintegrable mixed-field Ising chain on a timescale comparable to the onset of
quantum scrambling. Contrary to the typical spreading of information in this regime, the created burst is accompanied by a slow or even negative
entanglement growth. Analytically, we show that a burst becomes probabilistically rare after a long time. Our results suggest that a nonequilibrium state is maintained for an appropriately chosen initial state until scrambling becomes dominant. These predictions can be tested with programmable
quantum simulators.
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Mesoscale and Nanoscale Physics
Direct Visualization of Room-temperature Stair-stepped Quantum Spin Hall States in Bi4Br4
Zhiqiang Hu, Yuqi Zhang, Yuyang Wang et al. (+7 more)
Topological
insulators host exotic
quantum phenomena such as the
quantum spin Hall (QSH) effect, which enables dissipationless one-dimensional edge conduction. Realizing such states at room temperature and on a macroscopic scale is essential for energy-efficient electronics and
quantum technologies, yet remains a fundamental challenge due to material limitations. Here, using microwave impedance microscopy, we directly visualize robust QSH states persisting up to 300 K in {\alpha}-Bi4Br4 nanowires. This stability and scalability are enabled by a stair stepped stacking configuration, a multilayer geometry in which QSH edge states from individual layers remain spatially decoupled. This configuration circumvents the stringent
alignment and layer number constraints of previous proposals, allowing robust stair-stepped QSH (SS-QSH) conduction in structures several micrometers long and hundreds of nanometers high.
Magnetic field and temperature dependent measurements confirm their intrinsic topological nature. Crucially, the SS-QSH and bulk signals scale with nanowire height, verifying the stair stepped origin. Our results are also successfully reproduced by finite-element analysis simulations. This work establishes {\alpha} Bi4Br4 as a practical platform for high temperature topological electronics and demonstrates a generalizable stacking strategy for designing scalable QSH systems.
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All authors Zhiqiang Hu, Yuqi Zhang, Yuyang Wang, Kebin Xiao, Xiang Li, Zhiwei Wang, Huaixin Yang, Yugui Yao, Qi-Kun Xue, Wei Li
Superconductivity
Pressure-induced superconductivity beyond magnetic quantum criticality in a Kondo ferromagnet
Yanan Zhang, Yongjun Zhang, Jiawen Zhang et al. (+13 more)
Quantum phase transitions are an established setting for emergent phenomena driven by strong electronic correlations, including strange metals and unconventional superconductivity. These have been explored extensively in Kondo
lattice materials tuned to an
antiferromagnetic quantum critical point (QCP), but superconductivity emerging near
ferromagnetic quantum criticality is not yet observed, and the conditions under which it occurs in proximity to ferromagnetism are undetermined. Here, we report a new setting for superconductivity in the
ferromagnetic Kondo-
lattice material Ce5CoGe2, where there is a
ferromagnetic ground state at ambient pressure, which evolves to antiferromagnetism under applied pressures. The
antiferromagnetic transition is suppressed to a zero-temperature QCP, which is accompanied by strange-metal behavior. Superconductivity does not occur at the QCP, but instead appears at pressures beyond the
magnetic instability. These findings suggest that Ce5CoGe2 represents a distinct class of correlated materials exhibiting a unique scenario for the emergence of superconductivity, likely associated with unconventional pairing mechanisms beyond
spin-fluctuations.
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All authors Yanan Zhang, Yongjun Zhang, Jiawen Zhang, Kaixin Ye, Dajun Su, Yanen Huang, Zhaoyang Shan, Jiyuan Li, Rui Li, Ye Chen, Xin Lu, Lin Jiao, Yu Liu, Michael Smidman, Frank Steglich, Huiqiu Yuan
Materials Science
Cavity control of multiferroic order in single-layer NiI$_2$
Chongxiao Fan, Emil Viñas Boström, Xinle Cheng et al. (+5 more)
Controlling materials through their interactions with electromagnetic
vacuum fluctuations is an emergent frontier in material engineering. Although recent experiments have demonstrated dark cavity effects for electronic material phases, like superconductivity, ferroelectricity and charge density waves, a smoking gun experiment for
magnetic systems is lacking. Largely, this comes from the focus on phase transitions, where a large critical light-matter coupling is needed to observe cavity modifications. Here, we propose spiral magnets, where even a small cavity-mediated change in
magnetic interactions is reflected in a change of the spiral wavelength, as a promising platform to observe cavity effects. We focus on the single-layer multiferroic NiI$_2$, interacting with electric field fluctuations from surface
phonon polaritons of the paraelectric substrate SrTiO$_3$. With decreasing substrate-material distance, the ratio of nearest and third nearest neighbor exchange interactions reduces, leading to an increase of the spiral wavelength and an eventual transition into a
ferromagnetic state. Our work identifies a realistic platform to observe cavity
vacuum renormalization effects in
magnetic systems.
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All authors Chongxiao Fan, Emil Viñas Boström, Xinle Cheng, Lukas Grunwald, Zhuquan Zhang, Dante M. Kennes, Dmitri N. Basov, Angel Rubio
Superconductivity
Understanding critical currents in superconducting cuprate tapes
Charles Simon
One of the key challenges in the fabrication of superconducting coils using cuprate tapes is the parametrization of the critical currents and their dependence on
magnetic field, temperature, and angle. Discussions at the Magnet Technology Conference (MT29) in Boston (2025) highlighted the need for standardized characterization and a better understanding of these tapes. Without a shared understanding of the physical phenomena governing critical currents, progress in this area remains difficult. We propose to analyze existing data using a model that explains most observed features. Although the model proposed by P. Mathieu and Y. Simon was published 20 years ago, it remains relatively unknown and certainly unused among engineers in the field, although many physicists were convinced of its validity, a consensus not reflected in the literature. The Mathieu/Simon (MS) model emphasizes the importance of surface pinning mechanisms, which dominate critical currents across a large part of the phase diagram of YBaCuO. Unlike strong and weak pinning mechanisms, which are commonly assumed to be dominant, the MS model accurately predicts the order of magnitude of experimentally measured values, suggesting it should at least be considered the dominant mechanism. The results of calculations based on this model are presented and compared with experimental data, offering directions for the development of new materials.
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Soft Condensed Matter
Dynamic bidirectional coupling of membrane morphology and rod organization in flexible vesicles
Stijn van der Ham, André F. V. Matias, Marjolein Dijkstra et al. (+1 more)
The ordering of rod-like particles in soft, deformable containers emerges from the interplay of anisotropic interactions,
geometric confinement, and boundary compliance. This competition couples internal particle organization to container morphology, producing behavior distinct from both rigid confinement and bulk systems. Such coupling is also relevant to biological contexts in which filamentous structures are confined by deformable membranes. Using a minimal model combining experiments and simulations of colloidal rods encapsulated in lipid vesicles, we show that soft confinement drives a bidirectional coupling between internal order and vesicle shape. This interplay gives rise to a phase diagram in which elongated vesicles promote nematic
alignment at lower packing fractions, whereas higher packing fractions induce smectic-like ordering that reshapes vesicles into plate-like morphologies with increased bending energy. Furthermore, by controlling vesicle volume and membrane area, we demonstrate that boundary conditions enable reversible tuning of both vesicle shape and internal rod organization. These results establish a framework for dynamically controlling colloidal self-assembly in soft containers and provide insight into the organization of anisotropic building blocks in deformable,
cell-like, confinements.
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All authors Stijn van der Ham, André F. V. Matias, Marjolein Dijkstra, Hanumantha Rao Vutukuri
Soft Condensed Matter
Topological constraints suppress shear localization in granular chain ensembles
Palash Sarate, Mohd. Ilyas Bhat, Tejas G. Murthy et al. (+1 more)
Entangled granular systems exhibit mechanical
rigidity and resistance to deformation, reminiscent of cohesive materials, due to their reduced degrees of freedom and contact friction. A quantitative understanding of how classical granular phenomena, such as shear localization and plastic flow, appear in such geometrically cohesive systems remains unknown. Here, we investigate this using granular chain ensembles subjected to direct shear tests. Our experiments reveal that chains longer than four beads exhibit pronounced shear hardening, which is nearly independent of the applied normal stress and is accompanied by the complete suppression of shear localization. The volume dilation of the long chain ensembles also does not vanish in the steady state. We complement this phenomenology, which is distinct from that of typical frictional granular ensembles, with DEM simulations. The simulations reveal that tensile forces are generated due to particles being locally jammed, characterized by a high non-covalent coordination number. Consequently, this leads to a deformation that shows a very diffuse region of localization and enhanced shear hardening. Overall, our study highlights that granular chains provide a systematic route to map how connectivity constraints impact flow properties and mechanical
rigidity.
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All authors Palash Sarate, Mohd. Ilyas Bhat, Tejas G. Murthy, Prerna Sharma
Superconductivity
Optical conductivity signatures of strong correlations and multiband superconductivity in infinite-layer nickelates
Woo Jin Kim, Kyuho Lee, Eun Kyo Ko et al. (+6 more)
Since the discovery of superconductivity in infinite-layer nickelates, there have been extensive efforts to unravel their electronic structure and pairing mechanism. In particular, understanding how the electronic structure evolves with doping is essential for clarifying theoretical models of superconductivity in nickelates. Here we present studies of the optical conductivity of Nd1-xSrxNiO2 thin films spanning the full phase diagram 0.025 < x < 0.30 using spectroscopic ellipsometry. The data are consistent with a two-band Drude model, which allows the decomposition of the intraband response into distinct contributions. One is from a "narrow" Drude term which we associate with electron bands, and the other a "broad" Drude term linked to the hole band with strong correlations. Increasing Sr doping leads to an expansion of the hole band spectral weight, and a corresponding reduction in the electron band, indicative of the multiband electronic structure and a doping-dependent reconstruction of the
Fermi surface. Both doping and temperature-dependent optical spectra display significant spectral weight transfer from high to low energy, a hallmark of strong electronic correlations. In the superconducting state at optimal doping (x = 0.15), both electron and hole bands contribute to the superconducting condensate, signifying multiband superconductivity.
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All authors Woo Jin Kim, Kyuho Lee, Eun Kyo Ko, Jaeseok Son, Yonghun Lee, Yijun Yu, Soon Jae Moon, Tae Won Noh, Harold Y. Hwang
Materials Science · Cross-listed from physics.optics
Background-free Tracking of Ultrafast Hole and Electron Dynamics with XUV Transient Grating Spectroscopy
Vincent Eggers, Rafael Quintero-Bermudez, Kevin Gulu Xiong et al. (+1 more)
Extreme ultraviolet (XUV) transient absorption (TA) and transient reflectivity (TR) spectroscopies enable element-specific insights into attosecond-timescale processes in solids. XUV transient grating spectroscopy (TGS) is an emerging tool that combines the advantages of both absorption and reflectivity while offering intrinsically background-free detection. Here, we implement XUV-TGS by generating a transient grating in germanium solid using two few-cycle near-infrared pulses and probing it with an attosecond XUV pulse, produced via tabletop high-harmonic generation. The spectrally resolved, diffracted XUV pulses directly visualize the separate ultrashort decay times of both photoexcited electrons and holes, without the need for iterative deconvolution. By combining XUV-TA and -TG spectroscopy, we extract the
evolution of the complex refractive index, ñ, without the need for Kramers-Kronig reconstruction, as required in XUV-TR, allowing us to extract the roots of the induced optical response. We find reflectivity changes of up to 34% via the real part of ñ, whereas changes in the imaginary part only result in a variation in reflectivity of around 0.5%.
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All authors Vincent Eggers, Rafael Quintero-Bermudez, Kevin Gulu Xiong, Stephen R. Leone
Soft Condensed Matter
Modeling bacterial flow field with regularized singularities
Yaochen Yang, Daiki Matsunaga, Da Wei et al. (+1 more)
The flow field generated by a swimming bacterium serves as a fundamental building block for understanding hydrodynamic interactions between bacteria. Although the flow field generated by a force dipole (stresslet) well captures the fluid motion in the far field limit, the stresslet description does not work in the near-field limit, which can be important in microswimmer interactions. Here we propose the model combining an anisotropically regularized stresslet with an isotropically regularized source dipole, and it nicely reproduces the flow field around a swimming bacterium, which is validated by the experimental measurements of the flow field around E. coli and our boundary-element-method simulations of a helical microswimmer, in both cases of the free space and the confined space with a no-slip wall. This work provides a practical tool for obtaining the flow field of the bacterium, and can be utilised to study the collective responses of bacteria in dense suspensions.
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All authors Yaochen Yang, Daiki Matsunaga, Da Wei, Fanlong Meng
Materials Science
Chiralometer: Direct Torque Detection of Crystal Chirality
Nikolai Peshcherenko, Ning Mao, Claudia Felser et al. (+1 more)
Chirality governs phenomena ranging from chemical reactions to the
topology of quasiparticle charge carriers. However, a direct macroscopic probe for
crystal chirality remains a significant challenge, especially in time reversal symmetric systems with weak circular dichroism signal. Here, we propose the “Chiralometer”, a mechanical detection method that probes chirality by driving angular momentum carriers out of
equilibrium. Using first-principles calculations and semiclassical transport theory, we demonstrate that a temperature gradient in
insulators or an electric field in metals induces uncompensated angular momentum in
phonons and electrons, respectively. This imbalance generates a macroscopic mechanical torque ($\tau \sim 10^{-11} N \cdot m$) well within the sensitivity of modern torque magnetometry and cantilever-based sensors. We identify robust signatures in
chiral crystals such as Te, SiO$_2$, and the topological semimetal CoSi. Our work establishes mechanical torque as a fundamental order parameter for chirality, offering a transformative tool for orbitronics and
chiral quantum materials.
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All authors Nikolai Peshcherenko, Ning Mao, Claudia Felser, Yang Zhang
Mesoscale and Nanoscale Physics
Scattering theory of spin waves by lattice dislocation defects
Cristobal Larronde, Ignacio Castro, Alvaro S. Nunez et al. (+2 more)
We investigate
spin-wave propagation in
magnetic insulators in the presence of
lattice dislocations. Within a continuum magnetoelastic framework, we show that the strain fields generated by dislocations induce
equilibrium magnetic textures. The morphology of these textures depends sensitively on the dislocation type and acts as a localized scattering potential for
spin-wave excitations. As a result, the scattering response exhibits pronounced asymmetries and interference effects governed by the magnetoelastic coupling and the dislocation type. By combining numerical simulations with analytical scattering theory, we compute differential cross sections and frequency-dependent transmission coefficients. Furthermore, analysis of the effective potential landscape reveals that the defect forms a barrier that modulates
spin-wave transport and, crucially, breaks the intrinsic reflectionless nature of
magnetic domain walls. Our findings identify
lattice dislocations as tunable scattering centers, opening new avenues for defect engineering in magnonic devices.
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All authors Cristobal Larronde, Ignacio Castro, Alvaro S. Nunez, Roberto E. Troncoso, Nicolas Vidal-Silva
Strongly Correlated Electrons
Interaction-driven spin polaron in itinerant flat-band ferromagnetism
Wei-Tao Zhou, Zhao-Yang Dong and Jian-Xin Li
Interaction effects are dramatically enhanced in flat-band systems due to quenched kinetics, facilitating the binding of single excitations into composite quasiparticles. In this work, we present a comprehensive study of
spin polarons over the entire momentum and energy space within the Mielke-Tasaki model using projected exact diagonalization. We identify distinct low-energy
spin polarons at momenta q=0 and q=\pi, and also find multiple high-energy branches of
spin polaron. It is demonstrated that the interaction-induced Hartree dispersion plays a decisive role in determining the momentum sector of low-energy
spin polarons. Furthermore, by introducing a finite bandwidth, we unravel the underlying binding mechanisms: the formation of low-energy
spin polarons is governed by the conventional virtual exchange mechanism, whereas the high-energy
spin polarons arise from a joint effect of the effective attraction and virtual exchange. Our results suggest promising avenues for realizing
spin polaron
crystals and exploring novel superconducting pairing mechanisms in moiré materials like twisted WSe2 and MoTe2.
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Mesoscale and Nanoscale Physics
Origin of Moiré Potentials in WS$_2$/WSe$_2$ Heterobilayers: Contributions from Lattice Reconstruction and Interlayer Charge Transfer
Youwen Wang, Nanya Gao and Qingjun Tong
Moiré superlattices formed in WS$_2$/WSe$_2$ heterobilayers have emerged as an exciting platform to explore the
quantum many-body physics. The key mechanism is the introduction of moiré potentials for the band-edge carriers induced by the lateral modulation of interlayer interactions. This trapping potential results in the formation of flat bands, which enhances the strong correlation effect. However, a full understanding of the origin of this intriguing potential remains elusive. In this paper, we present a comprehensive investigation of the origin of moiré potentials in both R-type and H-type moiré patterns formed in WS$_2$/WSe$_2$ heterobilayers. We show that both
lattice reconstruction and interlayer charge transfer contribute significantly to the formation of moiré potentials. In particular, the
lattice reconstruction induces a nonuniform local strain, which creates an energy modulation of 200 meV for the conduction band-edge state located at WS$_2$ layer and 20 meV for the valence band-edge state located at WSe$_2$ layer. In addition, the
lattice reconstruction also introduces a piezopotential energy, whose amplitude ranges from 40 meV to 90 meV depending on the stacking and band-edge carrier. The interlayer charge transfer induces a built-in electric field, resulting in an energy modulation of 80 meV for an R-type moiré and 40 meV for an H-type moiré. Taking into account both effects from
lattice reconstruction and interlayer charge transfer, the formation of moiré potential is well understood for both R-type and H-type moirés. This trapping potential localizes the wavefunctions of conduction and valence bands around the same moiré site for an R-type moiré, while around different moiré site for an H-type one.
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Disordered Systems and Neural Networks
Finite integration time can shift optimal sensitivity away from criticality
Sahel Azizpour, Viola Priesemann, Johannes Zierenberg et al. (+1 more)
Sensitivity to small changes in the environment is crucial for many real-world tasks, enabling living and artificial systems to make correct behavioral decisions. It has been shown that such sensitivity is maximized when a system operates near the critical point of a phase transition. However, proximity to criticality introduces large fluctuations and diverging timescales. Hence, to leverage the maximal sensitivity, it would require impractically long integration periods. Here, we analytically and computationally demonstrate how the optimal tuning of a recurrent neural network is determined given a finite integration time. Rather than maximizing the theoretically available sensitivity, we find networks attain different sensitivities depending on the available time. Consequently, the optimal dynamic regime can shift away from criticality when integration times are finite, highlighting the necessity of incorporating finite-time considerations into studies of information processing.
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All authors Sahel Azizpour, Viola Priesemann, Johannes Zierenberg, Anna Levina
Materials Science
Competing magnetic states in a non-coplanar Kagome magnet
Xiaodong Hu, Amar Fakhredine, Roger Guzman et al. (+15 more)
Non-collinear Kagome antiferromagnets (AFMs) Mn3X (X = Sn, Ga, Ge, Ir, Pt) can generate an anomalous
Hall effect (AHE) despite vanishing net magnetization, enabled by broken time-reversal and inversion
symmetries. However, strong in-plane anisotropy has limited studies of the AFM-AHE and electronic applications to coplanar
spin configurations. Non-coplanar
spin textures in these systems have been realized only in low temperature
spin-glass states or at interfaces with heavy metals. Here, we report an intrinsic non-coplanar
spin configuration persisting up to 400 K in cubic-phase Mn3Ge, originating from coexisting symmetric and antisymmetric exchange interactions. Competing
magnetic states associated with this non-coplanar
spin configuration give rise to an unconventional AHE with a
magnetic-field-induced sign reversal and a hump-like feature. Our findings establish a platform for non-coplanar magnetism in AFM spintronics.
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All authors Xiaodong Hu, Amar Fakhredine, Roger Guzman, Martin Frentrup, Jinan Shi, Giulio I. Lampronti, Sami El-Khatib, Waichuen Tse, Laura Gorzawski, Angelo Di Bernardo, Nadia Stelmashenko, Wu Zhou, Mehmet Egilmez, Danfeng Li, Grzegorz P. Mazur, Mario Cuoco, Carmine Autieri, Jason W. A. Robinson
Mesoscale and Nanoscale Physics
Field-Dependent Qubit Flux Noise Simulated from Materials-Specific Disordered Exchange Interactions Between Paramagnetic Adsorbates
Keith G. Ray, Yaniv Rosen, Jonathan L Dubois et al. (+1 more)
Superconducting
quantum devices, from
qubits and magnetometers to dark matter detectors, are influenced by
magnetic flux noise originating from paramagnetic surface defects and
impurities. These
spin systems can feature complex dynamics, including a Berezinskii-Kosterlitz-Thouless transition, that depend on the
lattice, interactions, external fields, and disorder. However, the disorder included in typical models is not materials-specific, diminishing the ability to accurately capture measured flux noise phenomena. We present a first principles-based simulation of a
spin lattice consisting of paramagnetic O$_2$ molecules on an Al$_2$O$_3$ surface, a likely flux noise source in superconducting
qubits, to elucidate opportunities to mitigate flux noise. We simulate an ensemble of surface adsorbates with disordered orientations and calculate the orientation-dependent exchange couplings using density functional theory. Thus, our
spin simulation has no free parameters or assumed functional form of the disorder, and captures correlation in the defect landscape that would appear in real systems. We calculate a range of exchange interactions between electron pairs, with the smallest values, 0.016 meV and -0.023 meV, being in the range required to act as a two-level system and couple to GHz resonators. We calculate the flux noise frequency, temperature, and applied external
magnetic field dependence, as well as the susceptibility-flux noise cross-correlation. Calculated trends agree with experiment, demonstrating that a surface harboring paramagnetic adsorbates arranged with materials-specific disorder and interactions captures the various properties of
magnetic flux noise observed in superconducting
circuits. In addition, we find that an external electric field can tune the
spin-
spin interaction strength and reduce
magnetic flux noise.
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All authors Keith G. Ray, Yaniv Rosen, Jonathan L Dubois, Vincenzo Lordi
Materials Science
Realistic tight-binding model for V2Se2O-family altermagnets
Xingkai Cheng, Yifan Gao and Junjie Pengand Junwei Liu
Following earlier theoretical prediction, intercalated V2Se2O-family altermagnets such as RbV2Te2O and KV2Se2O have now been experimentally confirmed as d-wave altermagnets, representing the only known van der Waals layered altermagnetic systems. By combining
crystal-
symmetry-paired
spin-momentum locking (CSML) with the layered structure, the V2Se2O-family offers a suitable platform for studying low-dimensional spintronic responses and exploring the interplay among multiple
quantum degrees of freedom. To establish a concrete theoretical foundation for understanding and utilizing these materials, we investigate six representative members of the V2Se2O-family and construct a realistic tight-binding model parameterized by first-principles calculations, which is benchmarked by experimental measurements. This model accurately captures essential altermagnetic electronic properties, including CSML and noncollinear
spin-conserved currents. It further incorporates strain-coupling parameters, enabling the simulation of strain-tunable responses such as the piezo-
Hall effects. This realistic model allows systematic exploration of multiple degrees of freedom (like
spin, valley, and layer) within a single system, and lays the groundwork for understanding their coupling with other
quantum materials, such as topological
insulators and
superconductors, thereby advancing both the fundamental understanding and potential device applications of this novel class of layered altermagnets.
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Materials Science
Nodal-Surface and Flat-Band Driven Large Anomalous Nernst Effect in Epitaxial Ferromagnetic Weyl Metal Fe5Si3
Shubhashish Pati, Sonali Srotaswini Pradhan, Nanhe Kumar Gupta et al. (+7 more)
Magnetic topological materials such as Weyl and Dirac magnets exhibit unconventional electronic properties arising from the interplay between
magnetic order and band
topology, leading to remarkable thermomagnetic and thermoelectric effects. Here, we investigate the ANE in epitaxial thin films of the Weyl ferromagnet candidate Fe5Si3. A pronounced transverse Nernst response exceeding approximately 1.50 microvolt per kelvin is observed at room temperature, together with a
giant anomalous Nernst angle of about 0.56, indicating highly efficient conversion between thermal gradients and transverse electric fields. Beyond the anomalous contribution, a sizable topological Nernst signal of approximately 0.43 microvolt per kelvin persists above room temperature, suggesting the possible presence of real-space Berry
curvature associated with nontrivial
spin textures. First-principles density functional theory calculations combined with
symmetry analysis reveal an unconventional electronic structure in which Weyl nodal lines, nodal surfaces, and nearly flat bands coexist near the
Fermi level. This rare concurrence of multiple topological band features produces a strongly enhanced and sharply energy-dependent Berry
curvature, which governs both the magnitude and temperature
evolution of the observed Nernst response. The close quantitative agreement between calculated anomalous Nernst conductivity and experimental results establishes the topological electronic structure as the dominant origin of the observed thermomagnetic transport, highlighting Fe5Si3 as a chemically simple, low-cost binary topological magnet for exploring both real-space and momentum-space Berry-
curvature-driven thermoelectric phenomena.
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All authors Shubhashish Pati, Sonali Srotaswini Pradhan, Nanhe Kumar Gupta, Abhay Pandey, Nikita Sharma, Nakul Kumar, Saurav Singh, Yuya Sakuraba, V. Kanchana, Sujeet Chaudhary