Materials Science
A hidden low-temperature transformation pathway in compositionally complex materials
Yujiao Li, Elaheh Akbarnejad, Quentin Bizot et al. (+9 more)
Most compositionally complex materials (CCMs, frequently referred to as high
entropy alloys) are metastable and their attractive properties often belong to kinetically trapped states. However, pathways towards lower-free-energy phase states governing long-term stability, can remain hidden because
diffusion-controlled atomic redistribution is too slow to be revealed at experimentally accessible timescales. This blind spot is acute in CCM design: enormous compositional spaces are screened for performance, yet the low-temperature kinetics and the associated transformation pathways determining whether that performance persists are rarely considered in material selection. Here we use defect-rich nanoscale volumes coupled with atom-probe
tomography to access and reconstruct the hidden phase-
evolution pathway in a metastable Ag24Au20Pd50Pt6 electrocatalyst, without relying on elevated temperatures to accelerate the transformation. By varying microstructural starting state, annealing temperature and time, we reveal precipitation of a Pt-rich phase within the fcc
matrix, its coarsening and re-homogenization. The Pt-rich phase recurs after homogenization with delayed kinetic accessibility, while prolonged annealing extends the pathway to 300{\deg}C. Atomistic simulations independently predict the same Pt-rich phase selection. The transformation is accompanied by a 3.7-fold loss of catalytic activity for hydrogen
evolution. These results establish hidden phase-
evolution pathways as a materials-design variable: resolving them can guide the selection of metastable CCMs not only for their as-synthesized properties, but also for the phase states and associated functionalities they may access over time.
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All authors Yujiao Li, Elaheh Akbarnejad, Quentin Bizot, Aleksander Kostka, Natalia Pukhareva, Ridha Zerdoumi, Alan Savan, Matous Mrovec, Ralf Drautz, Baptiste Gault, Dierk Raabe, Alfred Ludwig
Mesoscale and Nanoscale Physics · Cross-listed from physics.optics
Nonlocal-nonlinear phonon polaritons
Gonzalo Álvarez-Pérez, Line Jelver, Alexander Paarmann et al. (+1 more)
When light is confined to deeply subwavelength volumes, optical responses can become nonlocal. Yet how nonlocality reshapes nonlinear light-matter interactions remains largely unexplored, particularly in dielectrics. Here, we theoretically uncover a new class of nonlinear optical processes arising from the interplay between optical-
phonon propagation and ionic-bond anharmonicity in polar
crystals. We show that, unlike conventional local nonlinearities, this mechanism enables second-order responses even in centrosymmetric materials. Moreover, these responses can be tuned by the confinement and resonantly enhanced near optical-
phonon resonances. Using density functional perturbation theory, we quantify the resulting nonlocal second-order susceptibilities in representative polar
crystals. Our results establish nonlocal-nonlinear optics as a new regime of light-matter interaction in dielectrics.
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All authors Gonzalo Álvarez-Pérez, Line Jelver, Alexander Paarmann, Simone De Liberato
Strongly Correlated Electrons
Influence of the inter-orbital interaction and kinetic terms on superconductivity: a simple two-orbital Hubbard model
Vito Marino, Diego Florez-Ablan, Luca F. Tocchio et al. (+2 more)
We investigate a minimal two-orbital Hubbard model with intra- and inter-orbital nearest-neighbor hopping $t$ and $\tilde{t}$, as well as intra- and inter-orbital density-density interactions $U$ and $U'$ by means of variational ansätze based on Jastrow-Slater wave functions within
quantum Monte Carlo techniques. To focus on the electronic mechanisms of superconductivity, we restrict the variational ansätze to uniform nonmagnetic states with an explicit pairing amplitude and compute the pairing correlations as a function of filling and model parameters. At $U/t=10$, superconducting correlations are highly enhanced by the presence of inter-orbital terms, $U'$ and $\tilde{t}$. For $\tilde{t}=0$, a finite value of $U'$ effectively screens the intra-orbital repulsion $U$, producing a shift in the superconducting dome. Consequently, inter-orbital repulsion yields a sizable increase in electron pairing compared to the single-orbital baseline. Furthermore, introducing a finite $\tilde{t}$ provides an additional boost to superconducting correlations, an effect driven by the simultaneous presence of flat and broad bands in the electronic structure.
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All authors Vito Marino, Diego Florez-Ablan, Luca F. Tocchio, Massimo Capone, Federico Becca
Superconductivity
Polireddi Naveen and Abhiram Soori
We theoretically investigate
equilibrium currents in a one-dimensional Josephson junction incorporating a bipolar
magnetic semiconductor (BMS). We show that the intrinsic exchange splitting of the
spin-resolved bands enables purely electrical control of the $0$–$\pi$ transition through gate-tunable modulation of the BMS chemical potential, eliminating the need for an external
magnetic field. This provides a viable route toward electrically tunable $\pi$-junction behavior and highlights the potential of BMS-based Josephson devices for phase-controllable superconducting electronics. Furthermore, in the presence of Rashba
spin–orbit coupling, we find an anomalous Josephson effect characterized by a finite
equilibrium supercurrent at zero phase difference. This behavior originates from the intrinsic breaking of time-reversal
symmetry associated with the
spin-polarized electronic structure of the BMS. Interestingly, despite the simultaneous breaking of time-reversal and inversion
symmetries—conditions often associated with nonreciprocal superconducting transport—we do not observe a Josephson diode effect. Our results therefore highlight an important distinction between anomalous Josephson transport and superconducting nonreciprocity: the former does not necessarily imply a finite critical-current asymmetry between opposite current directions.
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Disordered Systems and Neural Networks · Cross-listed from math-ph
Boundary Free Energies, Quenched Mixing, and Gibbs-State Selection in Disordered Ising Models
Mauris Chueng, Hexiang Wang and Keheng Zhu
We study boundary free energies and half-space responses in nearest-neighbor disordered Ising models. First, we prove the existence of fixed-depth tangential pressure and identify its derivative almost everywhere with the limiting boundary response. Second, under quenched exponential boundary-response mixing, we prove Gibbs-state selection independence and exponential convergence of finite-depth pressures. We further show that uniform one-
spin mixing yields DLR uniqueness and Gaussian normal localization, and verify the required mixing conditions whenever $(2d-1)\mathbb E\tanh(\beta\vert{}J\vert{})<1$. Finally, we establish an all-face surface limit in the bounded Dobrushin regime and provide counterexamples that delimit general surface and stiffness claims.
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Strongly Correlated Electrons
Critical bifurcation and deconfined quantum criticality in an interacting cluster Ising chain
Sourabh, Bachana Beradze, Mikheil Tsitsishvili et al. (+2 more)
We investigate the cluster Ising chain with an additional nearest-neighbor interaction using tensor-network methods and a weak-coupling field theory. Without the interaction, the Jordan-Wigner transformation decomposes the model into a triplet of identical Majorana chains related by an exact $O(3)$ flavor
symmetry. Their common mass vanishes at the $SU(2)_2$ Wess-Zumino-Novikov-Witten critical point with central charge $c = 3/2$ separating the
symmetry-protected topological cluster phase from a ferromagnet. The interaction reduces $O(3)$ to its cyclic subgroup $C_3$, splitting the triplet into a singlet and a doublet whose gaps close separately, producing a critical bifurcation into Ising ($c = 1/2$) and Gaussian ($c = 1$) critical lines. A second ferromagnetic phase opens between these critical lines for repulsive interactions and a disordered phase for attractive ones. The Gaussian line then separates two Landau-incompatible ferromagnets, realizing a deconfined
quantum critical line with emergent $O(2)$
symmetry, along which our independently extracted exponents vary continuously yet satisfy the parameter-free relation $\beta = (2\nu - 1)/4$ of the eight-vertex weak universality class. At stronger repulsion this line opens into an extended gapless floating phase with incommensurate algebraic correlations, entered through Berezinskii-Kosterlitz-Thouless transitions. All of these phases and the transitions between them are captured by the weak-coupling theory. Beyond its regime of validity, our simulations reveal a translation-
symmetry-breaking antiferromagnet reached through first-order transitions.
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All authors Sourabh, Bachana Beradze, Mikheil Tsitsishvili, Alexander Nersesyan, Titas Chanda
Materials Science
Off-stoichiometric variable doping for exceptional power factors in L2$_1$ Fe$_2$VAlM$_x$ (M=Ti, W) epitaxial thin films
Jose María Domínguez-Vázquez, Miguel Angel Tenaguillo, Ketan Lohani et al. (+7 more)
We show that the addition of Ti or W to stoichiometric L2$_1$ Fe$_2$VAl thin films by sputter codeposition produces off stoichiometric thin film
alloys with superior thermoelectric properties than their stoichiometric counterparts. Ti incorporation induces p-type semiconducting behavior, while W incorporation shifts the material toward n-type, hereby enabling simultaneous tuning of both carrier types within a single parent (Fe$_2$VAl) material system, making it highly desirable for thermoelectric devices. The introduction of both Ti and W partly substitutes V in the stoichiometric compound. The partial substitution of V in the stoichiometric
alloy allows fine-tuning the band structure of the system and transport properties. With this approach we obtain exceptional maximum power factor values for p and n-type films of 1300 $\mu$W/m$\cdot$K$^2$ and 2100 $\mu$W/m$\cdot$K$^2$ ,respectively, yielding maximum figures of merit zT of 0.07 and 0.14, respectively.
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All authors Jose María Domínguez-Vázquez, Miguel Angel Tenaguillo, Ketan Lohani, Jose J. Plata, Antonio M. Marquez, Olga Caballero-Calero, Alfonso Cebollada, Andrés Conca, Ernst Bauer, Marisol Martín-González
Materials Science
Influence of Interface Energy Anisotropy on the Solid-state Instability in Ni-based Superalloy: A Multiscale Study
Sourav Ghosh, Christian Brandl and Rajdip Mukherjee
The microstructural stability of nickel-based superalloys critically depends on the morphology and
evolution of $\gamma'$-precipitates, which is governed by elastic and interfacial anisotropies at the atomic scale. Here, we present a novel quantitative multiscale framework that, for the first time, directly incorporates atomistically computed interface energy anisotropy into mesoscale phase-field simulations to elucidate morphological selection and instability in the Ni–Al system. We employ density functional theory (DFT) to accurately predict the orientation-dependent $\gamma/\gamma'$ interface energies for key crystallographic planes. A rigorous analytic mapping is then developed to systematically reduce the three-dimensional (3D) interface anisotropy landscape to the two-dimensional (2D) simulation plane. This enables quantitative transfer of DFT-informed anisotropy parameters into a continuum phase-field model that also accounts for elastic inhomogeneity and eigenstrain. Our simulations demonstrate that the explicit inclusion of DFT-based interface energy anisotropy fundamentally alters precipitate morphological
evolution, robustly suppressing instability and faceting phenomena otherwise promoted by supersaturation and elastic effects. The framework bridges atomic- to mesoscale modeling, enabling predictive control of precipitate shapes and providing new insights into the interplay of elastic and interfacial contributions in Ni-based superalloys. This approach paves the way for quantitative microstructural design in advanced high-temperature
alloys via first-principles-guided multiscale simulation.
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Materials Science
Two Microscopic Mechanisms of Piezomagnetism in CoF$_2$ from First-Principles Calculations
Hiroshi Katsumoto, Tamio Oguchi and Kunihiko Yamauchi
Rutile-structured CoF$_2$ has long been recognized as a prototypical piezomagnetic material. Recently, it has attracted renewed interest as an altermagnet, exhibiting
spin-split electronic bands even in the absence of
spin-orbit coupling. Although the piezomagnetic response of CoF$_2$ has been extensively discussed from the viewpoint of
magnetic symmetry, its microscopic origin has remained elusive. First-principles calculations reveal two distinct microscopic mechanisms of piezomagnetism in CoF$_2$. Under $xy$ shear strain, the local volumes of the CoF$_6$ octahedra surrounding the two Co sites become different, leading to unequal
magnetic moments on the two sublattices and hence a net magnetization. In contrast, under $yz$ shear strain, the piezomagnetic response originates from
spin canting induced by the Dzyaloshinskii–Moriya interaction through
spin-orbit coupling. The presence of two distinct microscopic mechanisms may be a general feature of piezomagnetic antiferromagnets.
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Materials Science
Excitonic fingerprints of magnetic configurations and switching in multilayer CrSBr
Lukas Krelle, Ryan Tan, Jakob Conradi et al. (+6 more)
The coupling between electronic states and magnetism provides a route towards optical readout and control of
magnetic information. In the
magnetic semiconductor CrSBr,
excitons are coupled to
magnetic order, making their optical response sensitive to the underlying magnetization. Here, we show that the energy and oscillator strength of bulk and surface
excitons provide distinct spectroscopic fingerprints of
magnetic configurations and switching pathways. We distinguish domain-wall-mediated magnetization reversal, manifested by continuous spectral
evolution as a domain wall traverses the optical spot, from abrupt, large-area magnetization reversal. Using the resulting excitonic fingerprints, we reconstruct successive
magnetic configurations in 4- and 5-layer CrSBr during the transition from ferromagnetic to antiferromagnetic order. We further find that the sensitivity to
magnetic order is strongly
exciton-dependent: low-energy
excitons resolve intermediate and surface-related configurations, whereas a higher-energy
exciton predominantly exhibits a transfer of oscillator strength between ferromagnetic and antiferromagnetic resonances. These results establish excitonic spectroscopy as a sensitive probe of layer-dependent
magnetic configurations and their switching pathways in layered
magnetic semiconductors.
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All authors Lukas Krelle, Ryan Tan, Jakob Conradi, Priyanka Mondal, Wenze Lan, Kseniia Mosina, Regine von Klitzing, Zdenek Sofer, Bernhard Urbaszek
Statistical Mechanics
A Minimal Thermodynamically Consistent Chemical Oscillator
Benedikt Remlein, Luca Monari, Beatrice Bartolomei et al. (+3 more)
Inspired by the chemical reaction network considered as the smallest system featuring a Hopf bifurcation and its reversible extension, we introduce an even more minimal reaction network that is thermodynamically consistent and exhibits autonomous oscillations under nonequilibrium driving. The model combines three features that are rarely realized simultaneously in compact oscillator networks: a chemically plausible structure restricted to uni- and bimolecular reactions, reversibility of such reactions, and analytical tractability. The system consists of three internal species coupled to two chemostatted species and still undergoes a supercritical Hopf bifurcation when a chemostat concentration is varied. To analyze the dynamics and thermodynamics near the onset of oscillations, we employ the mathematical technique of normal-form reduction, which allows obtaining a controlled irreversible approximation that preserves the leading phase-space structure of the full reversible network while enabling explicit calculations. This framework provides analytical access to the bifurcation structure and the leading contributions governing thermodynamic observables. Within this setting, we use the onset of oscillations to characterize the thermodynamic response of the system. In particular, we offer an analytical description of key thermodynamic quantities such as the semi-grand Gibbs free energy and the non-conservative work rate, which exhibit a kink-like discontinuity at the Hopf bifurcation. We thus provide an analytical description of a phenomenon previously characterized only through numerical simulations of more complex networks.
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All authors Benedikt Remlein, Luca Monari, Beatrice Bartolomei, Giulio Ragazzon, Massimiliano Esposito, Emanuele Penocchio
Materials Science
Depth-Resolved Evolution of Buried Polar Topologies in a PbTiO3/SrTiO3 Superlattice
Xinxin Hu, Penghan Lu, Noa Varela-Dominguez et al. (+9 more)
Polar
topologies in complex oxides gives rise to a rich spectrum of emergent functionalities and are fundamentally governed by three-dimensional (3D) atomic structures. However, direct experimental determination of buried 3D polar configurations remains a longstanding challenge because conventional (scanning) transmission electron microscopy ((S)TEM) provides primarily projected structural information with limited depth sensitivity. Here, we combine depth-sectioning low-angle annular dark-field (LAADF) STEM, high-angle ADF (HAADF) STEM, and multislice electron ptychography (MEP) to directly visualize the depth-dependent atomic structure and polarization
topology in a PTO/STO superlattice. Depth-sectioning STEM reveals pronounced focal-depth-dependent contrast variations and apparent splitting of Pb atomic columns, indicating significant structural heterogeneity along the beam direction. MEP reconstruction simultaneously resolves the Pb, Ti, and O sublattices with nanometer-scale depth resolution, enabling quantitative mapping of atomic displacements throughout the reconstructed volume. The resulting 3D atomic model reveals substantial depth-dependent displacements of Pb, Ti, and O atoms and a corresponding
evolution of the polarization
topology.
Vortex-like polarization structures are observed near the specimen surfaces but become strongly suppressed within the interior, where distinct polarization configurations emerge. These findings show that polarization patterns observed in conventional projection images can arise from the superposition of multiple depth-dependent polar states and may obscure the underlying 3D polarization texture. Our findings establish a direct experimental link between local atomic displacements and depth-dependent polarization
topology, opening new opportunities for investigating and engineering buried functional states in complex oxide nanostructures.
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All authors Xinxin Hu, Penghan Lu, Noa Varela-Dominguez, Anthony Edgeton, Chang Beom-Eom, Francisco Rivadulla, José Santiso, Yingzhuo Lun, Zhihua Sun, Rafal Dunin-Borkowski, Gustau Catalan, Jordi Arbiol
Strongly Correlated Electrons
Frustration-induced degenerate spin state with up-up-down-down ordering in corner-connected Heisenberg square-plaquettes
Pritam Manna and A. K. Bera
We investigate frustrated magnetism of a corner-connected square plaquette Heisenberg model with exchange interactions along the edges $(J_1)$, along inter-plaquette links $(J_2)$, and along square diagonals $(J_3)$. Using Luttinger–Tisza (LT) minimization of the
Fourier interaction
matrix $\mathcal J(\mathbf q)$ together with large-scale Monte Carlo (MC) simulations, we obtain a classical low-temperature
magnetic phase diagram in the normalized plane $(J_1/|J_2|, J_3/|J_2|)$. The two methods play complementary roles: the LT analysis provides the zero-temperature candidate ordering wave vectors, while the MC simulations elucidate the resulting ordering tendencies under the hard-
spin constraint at low but finite temperatures. Three regimes emerge at low temperatures, an antiferromagnetic phase (AF), a ferromagnetic phase (FM) and a degenerate
spin state with up-up-down-down (uudd) ordering (DS). For the frustrated degenerate spinstate, LT exhibits line-like minima along $q_x=\pm q_y$ in the $hk$-plane, revealing a highly degenerate
spin configuration which violates the hard-
spin constraint. The MC results uncover a state with quasi-two-dimensional ordering. The DS regime is intrinsically multi-$\mathbf{q}$: the ordered texture assembles itself from
symmetry-related modes on the lines, producing a “uudd”
spin arrangement comprising of distinctive strong antiferromagnetic correlations on diagonals, ferromagnetic correlations on corner links, and highly suppressed correlations on the edges. The field-temperature phase diagram for a representative parameter point in the DS regime, determined by MC simulations, yields field induced distinct regions of negatively and positively correlated layers. These two regions are separated by a curve corresponding to negligible inter-layer correlations.
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Statistical Mechanics
Geometric Thermodynamics of Scallop Motion with Two Control Parameters
Hisao Hayakawa
According to Purcell's scallop
theorem, reciprocal single-degree-of-freedom shape deformations cannot achieve net propulsion in a viscous fluid. We show that this limitation is bypassed by thermal fluctuations in a two-parameter driven potential landscape. Formulating the
stochastic shape dynamics via a Smoluchowski equation with position-dependent mobility $M_\mathrm{eff}(x)$, we utilize a generalized inverse operator to evaluate the slow-driving response. Cyclic modulation of the control parameters induces a non-zero Berry-Sinitsyn-Nemenman
curvature $F_{12}(\bm{\theta})$, resulting in directed
geometric propulsion. Simultaneously, the non-adiabatic excess dissipation is dictated by a Riemannian thermodynamic metric $g_{ij}(\bm{\theta})$. Our results provide a unified
geometric foundation that bridges hydrodynamic friction,
stochastic mechanics, and thermodynamic trade-offs in micro-swimmers.
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Materials Science
Classification of Metal - Insulator Transitions: Relating characteristic Properties to Quantum Chemical Bonding Descriptors
Tim Bartsch, Carl-Friedrich Schön, Dasol Kim et al. (+3 more)
Pressure induced metal
insulator transitions (MIT) are classified by the
evolution of characteristic optoelectronic and vibrational properties calculated with density functional theory. Three classes emerge: ionic solids metallize continuously at band-gap closure with hardening
phonons; covalent solids show discontinuous changes in atomic arrangement and optical
phonon frequencies; a third class exhibits complete
lattice softening and drastically enhanced electron
phonon coupling. A one dimensional hydrogen chain reproduces this behavior and serves as a toy model of the underlying bonding mechanism, termed metavalent. Two
quantum-chemical descriptors capture the distinct bonding changes behind the three classes. In metavalent solids, competing electron localization and delocalization yield soft optical modes and Peierls distortions on the insulating side, superconductivity on the metallic side, and low
lattice thermal conductivity near the MIT.
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All authors Tim Bartsch, Carl-Friedrich Schön, Dasol Kim, Raagya Arora, Umesh Waghmare, Matthias Wuttig
Superconductivity
Phase-controlled perfect nonlocal spin and charge diode effects in a four-terminal Josephson junction with $p$-wave magnets
Lovy Sharma, Bimal Ghimire and Manisha Thakurathi
We theoretically investigate charge and
spin transport in a four-terminal Josephson junction with a normal-metal barrier. The top and bottom superconducting leads are equal-
spin triplet $p_y$-wave
superconductors, while the left and right leads are $p$-wave magnets with proximity-induced conventional $s$-wave superconductivity. When the transverse macroscopic phase difference between the top and bottom leads is set to zero, a longitudinal phase bias generates a pure transverse
spin current with perfect 100% nonreciprocity. Remarkably, a finite transverse phase difference preserves the perfect
spin-diode effect while simultaneously inducing a perfect charge-diode effect, enabling fully nonreciprocal
spin and charge transport. Moreover, the
spin-diode efficiency exhibits sharp, step-like switching as a function of both the gate voltage applied to the barrier and the crystallographic orientation of the $p$-wave magnet, providing independent and experimentally accessible knobs for controlling the diode polarity. The diode response remains robust against asymmetric interface couplings, nonmagnetic disorder, variations in the relative singlet and triplet pairing strengths, temperature, and junction dimensions, demonstrating that the effect is not a consequence of fine-tuned parameters. These findings establish the proposed four-terminal junction as a highly tunable and structurally robust platform for dissipationless, phase-controlled
spin and charge rectification, with potential applications in superconducting spintronics.
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Strongly Correlated Electrons
Neutron scattering evidence for two-dimensionally coupled spin-dimerized antiferromagnetic lattice in {\alpha}-Cu2P2O7
B. Ghanta, K. S. Chikara, M. Ghanathe et al. (+3 more)
The microscopic
magnetic model of the low-dimensional
quantum magnet alpha-Cu2P2O7 has remained controversial. We present a comprehensive study of its
magnetic ground state and excitation spectrum using temperature-dependent inelastic
neutron scattering,
neutron diffraction, magnetization measurements, and comprehensive
spin-wave modeling. Our results unambiguously establish alpha-Cu2P2O7 as a two-dimensionally coupled
spin-dimerized antiferromagnetic (AF)
lattice within the bc plane, with a dominant AF exchange J2 = 7.73 meV (hereafter referred to as "intradimer exchange") and weaker exchange couplings J1, J3, and J4 in the two-dimensional
lattice (hereafter referred to as "interdimer exchange"), in agreement with LDA-based density functional theory and in contrast to previous GGA+U predictions. The dominant intradimer AF exchange is found between seventh-nearest-neighbor Cu-Cu ion pairs [d(Cu-Cu) = 5.125(3) A] rather than nearest-neighbor Cu-Cu ion pairs [d(Cu-Cu) = 3.014(1) A] of the structural dimers. Weak interlayer coupling (J5 = 0.03 meV) stabilizes long-range antiferromagnetic order below TN = 25 K. We further identify a weak single-ion anisotropy, associated with the distorted CuO5 polyhedra, that opens a gap in the
spin-excitation spectrum and drives a field-induced metamagnetic transition. Systematic
spin-wave calculations elucidate the distinct roles of interlayer coupling J5 and anisotropy term D in producing two distinct energy gaps at different antiferromagnetic zone centers. Complementary
neutron diffraction and magnetization measurements as a function of applied
magnetic field uncover a previously overlooked metamagnetic transition near 13 kOe and allow construction of the
magnetic phase diagram in the H-T plane.
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All authors B. Ghanta, K. S. Chikara, M. Ghanathe, L. Keller, D. Voneshen, A. K. Bera
Materials Science
Bonding Signatures of Incipient Electron Localization in Topological Chiral Semimetals Near the Metal-Insulator Transition
Felix Hoff, Jonathan Frank, Mohit Raghuwanshi et al. (+11 more)
How do electronic localization and delocalization compete in solids beyond the traditional limiting cases of metals and iono-covalent
insulators? Topological chiral semimetals (TCSMs), characterized by their unique
crystal symmetry, offer an intriguing platform to explore this question. Here, we systematically compare TCSMs with covalent compounds, ordinary metals, and metavalent solids (incipient metals), and show that TCSMs occupy a distinct region in a multidimensional property fingerprint. Atom probe
tomography reveals an unusual bond-rupture signature, consistent with a bonding regime intermediate between electron localization and delocalization. This interpretation is supported by measurements of optical properties showing a transfer of spectral weight from interband to intraband transitions. For highly conductive TCSMs, this transition is accompanied by the disappearance of the Born effective charge, a measure of chemical bond polarizability, while less conductive TCSMs retain a nonzero value. Together, these results identify a property based bonding perspective on TCSMs that distinguishes them from metals, covalent solids, and metavalent compounds. Although metavalent solids and TCSMs both lie near the metal-
insulator transition and exhibit distorted
crystal structures, ultrafast coherent
phonon spectroscopy reveals fundamentally different
lattice-dynamical responses: a
phonon-driven Peierls-like instability in metavalent solids versus a robust chiral B20 bonding motif in TCSMs.
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All authors Felix Hoff, Jonathan Frank, Mohit Raghuwanshi, Jan Köttgen, Vicky Hasse, Tim Bartsch, Navjot Bamrah, Elias Hildebrand, Carl-Friedrich Schön, Kaustuv Manna, Chandra Shekhar, Claudia Felser, Ricardo P. S. M. Lobo, Matthias Wuttig
Mesoscale and Nanoscale Physics
Weaving Hopfions from Emergent Monopoles in a Chiral Magnet
Shoya Kasai, Kotaro Shimizu, Shun Okumura et al. (+1 more)
Recent advances in three-dimensional magnetization imaging techniques have opened new avenues for exploring topological
spin textures beyond domain walls and skyrmions. Among them,
magnetic hopfions are particularly promising, as their knotted
topology is expected to give rise to unconventional dynamics and responses; however, their controlled creation remains challenging. Here we propose a simple mechanism for generating hopfions from
magnetic torons, three-dimensional textures hosting an emergent monopole-antimonopole pair. Using Landau-Lifshitz-Gilbert simulations, we show that an electric current drives the annihilation of this pair, converting a toron into a hopfion. The initial toron length determines the number of generated hopfions, while the current direction selects the sign of the Hopf invariant. We further find that the threshold current depends sensitively on material parameters, indicating a close connection to skyrmion dynamics. Our results establish an experimentally accessible route to hopfion creation and reveal a pathway from monopole defects to knotted topological textures.
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All authors Shoya Kasai, Kotaro Shimizu, Shun Okumura, Yukitoshi Motome
Mesoscale and Nanoscale Physics
Composite fermions in the $\nu=3$ fractional quantum spin Hall effect
Hongquan Liu and D. E. Feldman
Well-understood fractional
quantum Hall states in GaAs and
graphene can be described in terms of weakly interacting composite
fermions. It is natural to expect that the same unifying principle applies to the putative fractional
quantum spin Hall effect in MoTe$_2$. Since the
quantum spin Hall effect involves two
spin components, two types of composite
fermions must be present. We classify all two-component composite-
fermion states at the filling factor $\nu=3$. The classification includes the three classes of states, which were introduced from different physical perspectives in Refs. Sodemann Villadiego, Phys. Rev. B 110, 045114 (2024), Jian et al., Phys. Rev. X 15, 021063 (2025), and May-Mann et al., Phys. Rev. B 111, L201111, (2025), as well as two new classes of states. A majority of the composite-
fermion states break the time-reversal
symmetry. We review quasiparticle charges, statistics, and edge theories for each possible state. We also address a way of identifying the experimentally relevant state or states. This can be accomplished by combining three probes. First, the shot noise technique provides information about fractional charges. Second, thermal conductance helps count edge modes. The third probe is based on a new idea and involves transport between two
quantum point contacts along a single edge. We find that the current from one contact to the other depends on the shape of the edge channel, which can be controlled with a side gate. The probe reveals the emergent
symmetry group of the low-energy edge theory.
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Quantum Gases · Cross-listed from nlin.PS
Stable rotating vortex clusters in three-dimensional quantum droplets
Liangwei Dong and Yaroslav V. Kartashov
We predict a new type of stable three-dimensional (3D)
vortex quantum droplets in binary Bose-Einstein condensate arranged into ring clusters that per-sistently rotate in the external potential. In contrast to clusters composed from localized
quantum droplets, the states introduced here represent interacting
vortex lines with identical topological charges nested in common 3D envelope and existing in much broader parameter range in comparison with local-ized
quantum droplets. The intricate interplay between mean-field nonlinearity of Bose-Einstein condensate,
quantum fluctuations described by Lee-Huang-Yang correction, Coriolis force arising due to rotation, and external potential leads to substantial variations of cluster shape upon increase of its rotation frequency. Rotating
vortex clusters bifurcate from single-
vortex quantum droplets and exist only above critical value of the rotation frequency that decreases with increase of chemical potential and depends on the number of
vortex lines in the cluster. The radius of the cluster decreases with increase of rotation frequency and weakly varies with chemical potential, which determines mostly localization of the individual
vortices in cluster and overall width of its envelope.
Vortex droplet clusters are very robust objects existing in stable form in wide intervals of the number of particles for any number (odd or even) of
vortex lines forming them. Our results may open the route to observation of stable arrays of
vortex lines of different configurations per-forming regular collective motion in condensate.
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Other Condensed Matter · Cross-listed from quant-ph
Time-Dependent Tunneling in the Thin-Barrier Limit
Tanmay Vachaspati, Frank Wilczek and Zara Yu
The usual WKB analysis for
quantum tunneling applies when the tunneling action is large, as it is for tall, wide potential barriers. In contrast we analyze tunneling when the action is small, as it is for tunneling across a tall, thin barrier. We develop a perturbative analysis where the control parameter is the inverse of the area under the potential barrier and apply our technique to several examples in $1+1$ dimensions. In resonant situations for bound particles we find that the tunneling probability grows with time as $\propto t^2$, while in non-resonant situations it grows linearly with time. We evaluate not only the tunneling probability but also the time-dependent tunneling wavefunction for a particle that escapes to infinity, i.e. from a quasi-bound state to the continuum.
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Mesoscale and Nanoscale Physics
Scattering-Induced Magnon Layer-Hall Transport beyond Band Geometry
Zhiping Xue, Zhoujian Sun, Xiyin Ye et al. (+2 more)
The layer Hall effect has been exclusively attributed to layer-locked Berry
curvature, posing a fundamental barrier to its realization in conventional magnets. Here we report a fundamentally distinct layer Hall effect for bosonic excitations, i.e.,
magnons, which originates solely from non-reciprocal dipolar scattering at heterointerfaces, thereby decoupling the phenomenon from
geometric-phase mechanisms. Using a microscopic scattering theory, we demonstrate that a longitudinal temperature gradient drives opposite transverse thermal Hall currents in a nanowire atop a
magnetic film, with the direction fully reconfigurable by the applied
magnetic field. The effect yields a significant Hall angle of $\sim 6^{\circ}$ in conventional
magnetic heterostructures, eliminating the need for topological engineering. Our findings establish a scattering-driven paradigm for layer Hall effect, extendable to ferrons and polar
phonons, and predict a Hall response that is readily detectable in conventional
magnetic heterostructures.
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All authors Zhiping Xue, Zhoujian Sun, Xiyin Ye, Lei Zhang, Tao Yu
Soft Condensed Matter · Cross-listed from physics.bio-ph
Quantifying the Biophysical Properties of Red Blood Cells in Gaucher Disease
Zhaojie Chai, Marine de Person, Pierre A. Buffet et al. (+2 more)
Gaucher disease (GD), the most common lysosomal storage disorder, alters red blood
cell (RBC) mechanics and circulation, contributing to vascular occlusions, bone infarcts, and splenomegaly. However, the individual roles of GD-RBC biophysical properties in these processes remain unclear. Here, we present a combined computational-experimental investigation to quantitatively characterize GD-RBC biophysical properties and determine how specific mechanical parameters drive abnormal RBC behavior. Informed by experimental data, we independently quantify key RBC properties, including shear modulus (mu), surface-to-volume ratio (S/V), and bending modulus (k_c). Based on these parameters, we construct three GD-RBC subtypes (GD-RBC1-3) to systematically isolate their individual contributions. At the single-
cell level, optical tweezers simulations show up to ~27% reduction in axial diameter and ~42% reduction in transverse compression. Tank-treading dynamics exhibit non-monotonic behavior, with rotation frequencies increasing by up to ~70% or decreasing under elevated bending rigidity. In confined flow, traversal times through microchannel constrictions increase by more than a factor of two, while splenic slit passage times rise from ~250 ms (control) to >1200 ms for the severe GD-RBC subtype, approaching a functional no-passage threshold. At the population level, viscosity simulations demonstrate that these alterations collectively elevate blood viscosity, with small fractions (~4.0%) of highly rigid
cells disproportionately increasing flow resistance. Overall, this study provides a quantitative and mechanistic framework that disentangles the contributions of key RBC parameters to abnormal behavior in GD, linking cellular-scale biophysics to hematologic dysfunction and microvascular occlusion.
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All authors Zhaojie Chai, Marine de Person, Pierre A. Buffet, Melanie Franco, George Em Karniadakis
Strongly Correlated Electrons
Quantum-geometry stabilization of dilute fractional Chern insulators
Ying-Xing Ding, Li-Min Zhang, Wen-Tong Li et al. (+2 more)
Fractional Chern
insulators have attracted broad interest as
lattice analogs of fractional
quantum Hall states without Landau levels. However, low-filling fractional Chern
insulators are fragile because charge-ordered phases can compete strongly with the fractional topological
liquid. Here, we propose a center-decorated kagome model, motivated by geometry-tunable artificial
lattices, in which the center-site hopping $t_2$ provides a direct knob for the
quantum geometry of an isolated $C=1$ flat band. Here
quantum geometry refers to the Berry
curvature and Fubini–Study metric, which determine the form factors of interactions projected into the Chern band. Exact diagonalization shows that tuning $t_2$ away from the flatness-optimized kagome limit reduces the trace-condition deviation, suppresses competing charge order, and enhances the many-body stability at both $\nu=1/3$ and the more fragile $\nu=1/5$ filling. At $\nu=1/5$, this stability-enhanced window persists under nearby interaction profiles, including variations of the dominant third-neighbor repulsion and weak nearest-neighbor admixtures. Low-energy spectra, spectral flow, quasihole and
entanglement counting, static structure factors, and the quantized total many-body Chern number $C_{\mathrm{tot}}=1$ consistently support Laughlin-like fractional Chern
insulators. These results identify
quantum-geometry engineering as a route to stabilizing dilute fractional Chern
insulators beyond band-flatness optimization alone.
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All authors Ying-Xing Ding, Li-Min Zhang, Wen-Tong Li, D. L. Zhou, Wu-Ming Liu
Materials Science
Engineering Dirac interface states
Gabriele Domaine, Moritz M. Hirschmann and Andreas P. Schnyder
We develop a low-energy theory of interface states in anisotropic multivalley Dirac systems whose masses and kinetic parameters are allowed to vary across an interface. For sharp interfaces, current-conserving matching conditions yield analytic expressions for the existence, localization and dispersion of the bound states. We show that the interface velocity is determined by the weighted tangential kinetic terms on the two sides of the seam. Their cancellation can suppress the linear velocity and generate an interface band that is flat to leading order near the projected Dirac point. For the special antisymmetric configuration in which both the Dirac mass and the tangential kinetic coefficient reverse sign with unchanged magnitude, the transparent sharp-interface solution is exactly dispersionless for all conserved momenta within the linear Dirac theory, while the surrounding bulk bands remain dispersive. We extend the theory to smooth interfaces, where the modified bound-state envelope changes the linear interface velocity through a spatial average of the tangential kinetic coefficient. We also investigate quadratic corrections in the kinetic \(\sigma_x\) and \(\sigma_y\) channels. To first order in their coefficients and through linear order in the interface momentum, these terms shift the interface-state energy but produce no additional correction to the linear velocity. Finally, we combine continuum and
lattice models to show how interface modes from distinct valleys hybridize and how the resulting dispersions depend on microscopic interface properties. Our results establish design principles for controlling the dispersion, localization, and hybridization of Dirac interface states. We further examine two
graphene-based mass-domain-wall models as experimentally inspired examples of dispersive copropagating and counterpropagating interface states.
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Disordered Systems and Neural Networks
Arithmetic Tuning of Dynamical Critical Exponents in Quasiperiodic Localization Transitions
Tian-Cheng Yi, Yi-Fan Liu, Enguo Guan et al. (+1 more)
The critical exponents and universality classes of localization transitions in quasiperiodic systems are of fundamental importance for understanding critical phenomena in aperiodic systems. Here we show that the dynamical critical behavior can be tuned without adding new terms or changing the form of the
Hamiltonian, but solely by varying the incommensurate frequency of the quasiperiodic onsite potential. We construct a family of incommensurate frequencies from the limiting ratios of generalized Fibonacci sequences controlled by the parameters $(m,n)$, and use them to define the quasiperiodic onsite potential. By combining generalized fidelity susceptibility, localization-length scaling, and finite-size gap analysis, we find that the correlation-length exponent is insensitive to the choice of the incommensurate frequency and remains consistent with the correlation-length critical exponent, $\nu \simeq 1$, in the localization transition of the standard Aubry–Andr'e–Harper model. In contrast, the dynamical exponent extracted from the low-energy gap scaling varies systematically with the incommensurate frequency. Our results show that changing the incommensurate frequency provides a simple way to tune dynamical critical scaling in deterministic aperiodic systems. Our results suggest instead that the arithmetic structure of an irrational number can serve as a control parameter for nonequilibrium
quantum dynamics, enabling the tuning of dynamical critical behavior without changing the microscopic
Hamiltonian or the physical spatial dimension.
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All authors Tian-Cheng Yi, Yi-Fan Liu, Enguo Guan, Wen-Long You
Quantum Gases
Tunable Mediated Interactions Near Spontaneous Symmetry Breaking: From Yukawa to Coulomb and Dzyaloshinskii–Moriya Interactions
Hoshu Hiyane and Hiroyuki Tajima
We propose a realization of tunable long-range mediated interactions generated by Nambu-Goldstone (NG) modes near spontaneous
symmetry breaking. An effective exchange interaction emerges between two distinguishable impurities proportional to the retarded susceptibility mediated by the bath particles. The interaction is mediated by emergent NG modes associated with
symmetry breaking in systems, namely the
magnon mode in a repulsive two-component Fermi or Bose gas, or the goldstino mode in a Bose-Fermi mixture. When the NG mode is gapped by explicit
symmetry breaking, the interaction has a Yukawa-type short-ranged interaction, whereas the gapless limit gives a Coulomb law. Above the NG mode threshold, the Dzyaloshinskii-Moriya-like cross product coupling emerges in a long-range form. Our proposal paves a way towards the realization of a
quantum simulator of
spin models and polarons with controllable non-local interactions.
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Statistical Mechanics
Bulk Phase Transition and Edge Behavior in Temporally Correlated Random Matrices
Masato Hisakado and Takuya Kaneko
We study long-range correlated Wigner-type
matrices built from row-independent stationary Gaussian sequences. For exponentially decaying (AR(1)) correlations, the bulk spectral density deforms from the semicircle law via an explicit combinatorial "hub" mechanism, yet we verify the flatness and decay hypotheses of the
matrix-Dyson-equation framework (MDE), with numerical evidence supporting Tracy-Widom edge universality for every fixed $\rho<1$ of the exponential decay correlations; the degenerate limit $\rho\to1^-$ reduces to a symmetrized Volterra operator, connecting to the singular-value cascade identified in a companion BBP analysis. For power-law correlations $dt\sim t^{-\gamma}$, we identify $\gamma_c=1/2$ as the critical point for divergence of the bulk fourth-moment, while $\gamma=1$ marks the breakdown of the flatness condition governing the MDE edge analysis. We prove the fourth-moment transition exactly and find numerically that the self-consistent edge varies smoothly across $\gamma=1$, with no evidence of a kink or discontinuity.
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Soft Condensed Matter
Collective Order Decouples Boundary Selection from Macroscopic Chirality in Confined Active Matter
Néstor Sepúlveda
Can a boundary determine the direction of circulation in a collectively moving active fluid? We study chiral self-propelled particles with nematic bulk
alignment, confined by walls whose orientational coupling varies continuously from nematic to polar. For an isolated particle at a wall, we derive the exact parameter condition under which a stable orientation is tangent to the wall. With predominantly nematic wall coupling, however, the many-body circulation changes sign at a chirality that is nearly independent of the wall
symmetry. This sign change follows a pronounced decrease in nematic order and disappears when bulk
alignment is removed. As the polar wall coupling becomes dominant, opposite-handed circulation is suppressed and same-handed polar locking emerges. Thus local orientation at a wall and the direction of macroscopic circulation are selected by distinct physical processes: the wall determines the possible local orientations, whereas collective order determines whether those orientations control the global flow.
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