We report spatiotemporally resolved measurements of flux avalanche dynamics in bulk superconducting NbTi using high-speed magneto-optical imaging. Tracking individual avalanche events reveals propagation velocities of 15–25 m/s, which are orders of magnitude slower than the km/s speeds observed in thin films. Analysis of characteristic time scales reveals that these avalanches are governed by local heating and limited heat dissipation through the adhesive layer, establishing a fundamentally different, thermally limited propagation regime. The threshold field for avalanche nucleation decreases with temperature, contrary to the increasing trend in thin films with efficient cooling—a behavior consistent with slow heat removal and thermal runaway in our system. All observed avalanches exhibit universal normalized velocity-distance scaling despite varying morphologies, confirming the robustness of thermal control. These findings reveal that bulk superconductors with poor thermal coupling operate in a previously uncharacterized avalanche regime, with direct implications for flux stability and quench protection in NbTi-based magnets, as well as a broader understanding of thermomagnetic instabilities in technological superconductors.

Recent studies have highlighted the role of flat bands and Van Hove singularities in enhancing electronic correlations, which can influence unconventional superconductivity. Here, we present a computational study of a two-dimensional superconductor on the square-octagon lattice, a geometry characterized by multiple flat bands, Van Hove singularities, and magnetic-flux tunable band dispersion. Using the Bogoliubov–de Gennes formalism, we investigate the effects of next-nearest-neighbor (NNN) hopping and Rashba spin-orbit coupling (SOC) on the superconducting state. We compute superconducting phase diagrams, emphasizing the impact of a high density of states on the order parameter, and examine the robustness of the two superconducting domes previously reported under variations in NNN hopping and SOC. We further evaluate the superfluid stiffness and study the Rashba SOC induced spin-triplet pairing correlations coexisting in the presence of the singlet order. Additionally, for weak attractive interactions, we demonstrate the enhancement of the critical temperature by varying the NNN strength, and we analyze how superconductivity evolves with increasing interaction strength. Finally, we revisit the proposal that the two-dome superconducting phase observed in unconventional systems may arise from a single pairing mechanism.

Representing real-time data as a sum of complex exponentials provides a compact form that enables both denoising and extrapolation. As a fully data-driven method, the Estimation of Signal Parameters via Rotational Invariance Techniques (ESPRIT) algorithm is agnostic to the underlying physical equations, making it broadly applicable to various observables and experimental or numerical setups. In this work, we consider applications of the ESPRIT algorithm primarily to extend real-time dynamical data from simulations of quantum systems. We evaluate ESPRIT's performance in the presence of noise and compare it to other extrapolation methods. We demonstrate its ability to extract information from short-time dynamics to reliably predict long-time behavior and determine the minimum time interval required for accurate results. We discuss how this insight can be leveraged in numerical methods that propagate quantum systems in time, and we show how ESPRIT can predict infinite-time values of dynamical observables, offering a purely data-driven approach to characterizing quantum phases.

Resonant inelastic x-ray scattering (RIXS) is a synchrotron-based spectroscopy that has seen growing interest across a range of scientific disciplines beyond fundamental physics. The interpretation of experimental RIXS data requires theoretical calculations based on the Kramers–Heisenberg formula. However, because of the dependence of RIXS on both the incident and scattered photon properties, a tractable treatment of the angular dependence in this formula has been lacking. In this work, within the electric-dipole approximation, we determine the number of fundamental spectra contributing to the RIXS cross section for all crystallographic point groups. We then derive a general expression for the RIXS cross section of isotropic samples such as untextured powders, homogeneous glasses or liquids, explicitly accounting for the polarization and propagation directions of both the incident and scattered photons. Simplified forms of the RIXS expressions are subsequently obtained for the most common point groups. Finally, we demonstrate the applicability of our formalism through two cases: $2p3d$ RIXS of ${\mathrm{Ni}}^{\mathrm{II}}$ and the study of uranium $3d4f$ RIXS.

We study the ferromagnetic instability in an $\mathrm{SU}\left(N\right)$ Fermi-Hubbard model on the hypercubic lattice. Combining dynamical mean-field theory with continuous-time quantum Monte Carlo simulations, we find that, in the strong-coupling regime at low temperatures, ferromagnetically ordered (FM) states develop away from the commensurate fillings. In the particle-doped SU(3) system near one-third filling, the FM state is accompanied by a spontaneous flavor-selective Mott state, where two of the three flavors are Mott insulating while the remaining flavor is metallic. Since particles in the metallic flavor can almost freely move on the lattice without correlation effects, the ordered state is stabilized by the kinetic-energy gain of the doped particles. This is similar to the generalized Nagaoka ferromagnetism discussed in the one-hole-doped system at one-third filling. In the SU(4) case, we find that six distinct types of FM states appear as the particle density varies. The results uncover the nature of the FM state in the $\mathrm{SU}\left(N\right)$ Fermi-Hubbard systems and highlight the rich magnetic behavior enabled by enlarged internal symmetries.

The recent discovery of superconductivity under pressure in Ruddlesden-Popper (RP) nickelates has attracted a great deal of attention. Here, using charge-self-consistent density-functional theory plus dynamical mean-field theory, we study the correlated electronic structure of the latest superconducting member of the family: the alternating single-layer bilayer nickelate ${\mathrm{La}}_5{\mathrm{Ni}}_3{\mathrm{O}}_{11}$. Due to its alternating single-layer and bilayer structural motif, this hybrid RP nickelate exhibits layer-selective physics with the single-layer neighboring a Mott instability, rendering the bilayer the dominant contributor to its low-energy physics at both ambient and high pressure. The electronic structure of ${\mathrm{La}}_5{\mathrm{Ni}}_3{\mathrm{O}}_{11}$ ultimately resembles that of the bilayer compound ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$, pointing to the presence of universal features in the family of superconducting RP nickelates. Thus, ${\mathrm{La}}_5{\mathrm{Ni}}_3{\mathrm{O}}_{11}$ provides a new platform to disentangle the key degrees of freedom underlying superconductivity in pressurized RP nickelates, underscoring the central role of the bilayer structural motif.

Motivated by recent angle-resolved photoemission spectroscopy (ARPES) experiments, we analyze the temperature, frequency, and momentum dependence of the single-particle scattering rate in a model of the $\gamma$-band of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ under strain, with particular emphasis on the behavior near the Lifshitz transition where the Fermi energy crosses a single Van Hove point. While the scattering rate is only moderately anisotropic at zero strain, we find that it becomes strongly anisotropic at the Lifshitz point. At the lowest energies, we recover the expected universal behavior: the scattering rate varies (ignoring logarithmic corrections) as ${\tau }^{-1}\sim \omega$ at the Van Hove point and as ${\tau }^{-1}\sim {\omega }^{3/2}$ away from it. At higher energies, however, corrections of order ${\omega }^2$ become important in both regimes. We show that the experimentally observed behavior ${\tau }^{-1}\sim {\omega }^{\alpha }$ with $\alpha \approx 1.4\left(2\right)$ at the Van Hove point can be quantitatively explained by a superposition of linear and quadratic contributions to the scattering rate, which are comparable in magnitude at the intermediate energies probed by experiment, rather than in terms of a new universal power law. We further predict a distinctive anisotropy, strain dependence, and a nonmonotonic frequency dependence of the scattering rate at a Lifshitz transition, all of which may be directly tested in experiments.

Moiré lattices attract significant attention in double-layer graphene and transition metal dichalcogenides (TMD) layer heterostructures as well as in photonic crystals due to the interesting exotic physics that emerges within these structures. In this work we report the strong coupling between excitons in ${\mathrm{CsPbBr}}_3$ microplates and moiré photonic modes at room temperature. Staggered moiré polariton states in different Bloch bands are directly measured. Increasing the pumping density, we observe moiré polariton condensation in the higher-energy bands. Importantly, with increasing the coupling strength between the twisted photonic lattices, we can tune the moiré polariton condensate from an insulating phase with short-range spatial coherence to a long-range spatial coherent state. The first-order coherence time is also increased by approximately 10%. Our work is generic for different moiré photonic lattices and lays the foundation to study coherent moiré polariton condensation at room temperature.

We theoretically investigate the transient spectral function during the photoinduced melting of charge order in a correlated electron system, to unravel the dynamical processes triggered by different initial excitations. We employ a one-dimensional interacting spinless fermion model introducing a pulsed laser light, and perform a comparative study by the Hartree-Fock approximation and by the exact diagonalization method to numerically solve the time-dependent Schrödinger equation. We find characteristic behavior in the transient spectral function, whose features strongly depend on the pump light frequency ${\omega }_p$. When ${\omega }_p$ is resonant with the collective phase mode of frequency ${\mathrm{\Omega }}_c\simeq {\mathrm{\Delta }}_{\mathrm{CO}}/2$, where ${\mathrm{\Delta }}_{\mathrm{CO}}$ is the charge gap, the transient spectral function exhibits a photoinduced in-gap weight that triggers large responses. With increasing laser intensity, the development of in-gap weight directly turns into the collapse of the gap. This charge-order destabilization process is in sharp contrast to the case of ${\omega }_p>{\mathrm{\Delta }}_{\mathrm{CO}}$, where the photoirradiation induces interband electron-hole excitations giving rise to a shrinkage of the gap. The impact of quantum fluctuations and spatial inhomogeneity on the photoinduced dynamics is also discussed.

This paper constitutes a sequel to our theoretical efforts to determine the nature of generic low-energy deformations of the Fermi surface of a quantum-critical metal, which arises at the stable non-Fermi liquid (NFL) fixed point of a quantum phase transition. The emergent critical Fermi surface, arising right at the Ising-nematic quantum critical point (QCP), is a paradigmatic example where an NFL behavior is induced by the strong interactions of the fermionic degrees of freedom with those of the bosonic order parameter. It is an artifact of the bosonic modes becoming massless at the QCP, thus undergoing Landau-damping at the level of one-loop self-energy. We resort to the well-tested formalism of the quantum Boltzmann equations (QBEs) for identifying the excitations. While in our earlier works, we have focused on the collisionless regime by neglecting the collision integral and assuming the bosons to be in equilibrium, here we embark on a full analysis. In particular, we take into account the bosonic part of the QBEs as well, which, however, turn out to have no effect on the solutions. Decomposing the master equation into angular-momentum ($\ell$) channels, the emergent modes are of two types: Fermi-surface deformations with discrete spectra and particle-hole excitations forming a continuous band. The long-lived zero-sound mode, which corresponds to $\ell =0$, is found to be robust against damping effects. Intriguingly, we have an infinite family of discrete modes corresponding to higher-order harmonics of the net deformation.

Describing the electronic and excitonic properties of two-dimensional metallic materials is challenging due to the reduced dielectric screening, which enhances many-body interactions and influences the optical response. In this work, we present a comprehensive study of many-body effects on the optical properties of two-dimensional (2D) metallic MXenes—a large family of emerging layered materials with significant potential for optoelectronic, sensing, and energy-harvesting applications. Using state-of-the-art methods, we explicitly treat intraband transitions and make use of a full frequency description of the screened Coulomb interaction, two aspects that are particularly important when treating many-body effects in metals. Our results reveal that many-body effects substantially modify the band structures of these metallic monolayers, reflecting the limited screening characteristic of atomically thin systems. The GW corrections lead to pronounced changes in the absorption spectra already at the independent-particle level. In contrast, the inclusion of electron-hole interactions through the Bethe-Salpeter equation (BSE) produces comparatively smaller modifications, which we attribute to the finite density of states at the Fermi level in these metallic systems. Overall, our findings highlight the necessity of explicitly accounting for many-body interactions to achieve reliable predictions of the optical properties of 2D metallic materials, and they establish key design principles for MXene-based optoelectronic applications.

Regardless of the model and platform details, critical phenomena exhibit universal behaviors that are remarkably consistent across various experiments and theories, resulting in a significant scientific success of condensed matter physics. One widely known and commonly used example is the two-dimensional (2D) quantum Hall transition; however, its universal exponents still somewhat conflict between experiments, theoretical models, and numerical ansatzes. We study the critical behaviors of quasi-2D Weyl semimetal systems with a finite thickness $L_z>1$, disorder, and external magnetic field $B_z$. By analyzing the scaling behaviors of the localization lengths and local density of states using recursive methods, we find that the finite thickness yields a deviation from the 2D quantum Hall universality ($L_z=1$ case) and a crossover toward the three-dimensional (3D) Gaussian unitary ensemble ($L_z\to \infty$ limit), potentially offering another cause of the discrepancy. Our work demonstrates the often-overlooked importance of auxiliary degrees of freedom, such as thickness, and that 3D quantum Hall physics is not merely a trivial finite-thickness extension of its 2D counterpart.

The unconventional π magnetism emerging at the edges of zigzag graphene nanoribbons (ZGNRs) has attracted considerable interest in carbon-based spintronics, motivating extensive efforts to understand and manipulate their spin distributions. Inspired by the recent discovery of electrically switchable ferroelectricity via interlayer sliding in multilayer graphene with more than three layers [L. Yang et al., Phys. Rev. Lett. 131, 096801 (2023)], we propose a nonvolatile and electrically switchable approach to modulate the magnetic properties of the ZGNR through heterostructure engineering with multilayer graphene. Using first-principles calculations, we demonstrate that when the ZGNR is positioned as either a surface layer or an internal layer in ABA stacking with adjacent layers, the stacking-induced charge redistribution creates a sublattice imbalance, leading to spin splitting. Furthermore, this spin splitting can be effectively modulated by polarization reversal through interlayer sliding. Specifically, in-plane polarization reversal is predicted to switch the spin splitting direction, while out of plane polarization reversal may either alter the presence of spin splitting or reverse its direction, depending on the stacking configuration. Our work provides a strategy for ferroelectric control of spin splitting in the ZGNR, demonstrating its potential as a key platform for nanoscale spintronic devices.

Cove-type edged graphene nanoribbons (CGNRs), constructed by removing several consecutive carbon atoms at both edges of each supercell in zigzag graphene nanoribbons, have attracted considerable interest due to recent advances in bottom-up synthesis and their intriguing quantum phenomena. However, their electronic transport properties remain poorly understood. Here, we perform a comprehensive theoretical study of CGNRs characterized by four structural parameters of nanoribbon width $N$, cove length $l_{\mathrm{c}}$, outermost zigzag-segment length $l_{\mathrm{z}}$, and cove offset $d$ between opposite edges. Our results reveal that nearly all CGNRs exhibit semiconducting behavior, except for metallic configurations with even $N$ and $l_{\mathrm{c}}+l_{\mathrm{z}}=2d$. The bandgap is continuously tunable over a wide range and presents a nonmonotonic dependence on the parameters of $l_{\mathrm{c}}, l_{\mathrm{z}}$, and $d$. In particular, the normalized bandgap can be described by a single parameter of the ratio $d/(l_{\mathrm{c}}+l_{\mathrm{z}})$, which is well fitted by a cosine function. In the presence of edge defects, a transmission gap opens in metallic CGNRs, while robust, quantized conductance peaks persist in the transmission spectra despite an overall reduction in transmission. These results provide general insights into the structure-property relationships of CGNRs and may facilitate engineering graphene-based electronic devices.

Periodically driven Floquet quantum systems hold great promise for engineering exotic quantum phases and matter, but are often limited by rapid thermalization. In this work, we propose and demonstrate a square-wave-modulated Floquet engineering protocol to steer and study the thermalization dynamics in one-dimensional Rydberg atom arrays. We identify a reciprocal Floquet thermalization mechanism, which is triggered when the combination of laser detuning and Rydberg atom interactions inversely matches the Floquet period. The level statistics show narrow peaks when the reciprocal condition is met, while thermalization is suppressed between two adjacent peaks. We extract signatures of thermalization and its suppression from the stroboscopic evolution of the atomic population. Critically, thermalization occurs in a disorder-free regime, with rapid equilibration achieved within the Rydberg lifetime and experimentally accessible initial states. Our study establishes a robust framework for exploring thermalization-to-localization transitions and designing effective Hamiltonians, and highlights the unique potential of the Rydberg atom array setting for quantum simulations.

We demonstrate deterministic, field-free magnetization reversal of a single-domain nanomagnet within 300 ps under a current density of $3\times {10}^{10}{\text{A/m}}^2$ by coupling reinforcement learning (RL) to the Landau-Lifshitz-Gilbert equation with the spin-orbit torques (SOTs). The RL agent autonomously discovers a current waveform that minimizes the magnetization trajectory path and exploits a precessional shortcut enabled by the fieldlike SOT and hard-axis anisotropy. From the learned pulse, we extract a clear physical picture of the dynamics and develop a model-based analytical framework that establishes a lower bound on the switching time. The control strategy remains robust across a wide range of damping constants and is stabilized against thermal fluctuations at higher current densities. We also discuss feasible experimental implementations for the precessional switching.

Introduction. The spin-ladder compounds of the ${\mathrm{BaFe}}_2{X}_3$ ($X$ = chalcogen) family may be viewed as dimensional reductions—along stripelike motifs—of the two-dimensional iron-based pnictide planes extensively studied since 2006. Remarkably, despite their reduced dimensionality, these materials retain the capacity for unconventional ground states, exemplified by the emergence of superconductivity in ${\mathrm{BaFe}}_2{\mathrm{Se}}_3$ under applied pressure beyond 10 GPa, following a structural phase transition at 4 GPa. Here, we report a comprehensive investigation combining high-resolution single-crystal x-ray diffraction, infrared spectroscopy, and ab initio calculations, which together elucidate the true crystallographic nature of this pressure-induced superconducting phase. While x-ray diffraction alone reveals a symmetry lowering from the widely accepted orthorhombic $Cmcm$ group to a monoclinic structure, it lacks sufficient sensitivity to resolve the precise space group. By integrating vibrational spectroscopy with density functional theory, we provide unambiguous evidence that the high-pressure phase is noncentrosymmetric, adopting the polar space group $P{2}_1$. These findings not only revise the structural assignment of ${\mathrm{BaFe}}_2{\mathrm{Se}}_3$ in its superconducting state, but also establish its noncentrosymmetric character—an essential ingredient for potential unconventional pairing mechanisms—thereby opening different perspectives on the interplay between lattice symmetry, dimensionality, and superconductivity in iron-based materials.

We observe microwave nonreciprocal one-way transparency via ultrastrongly coupled magnetochiral polaritons (MChPs) in a metamolecule at room temperature. The experimental results using MCh metamolecules with simultaneous breaking of time-reversal and space-inversion symmetries are reproduced by numerical simulations. Based on effective polarizability tensor analyses, we verify massive synthetic motion of MChPs as an origin of the one-way transparency. This study paves a way to hybrid quantum systems and synthetic gauge fields using metamaterials.

Floquet engineering is a powerful manipulation method in modern quantum technology. However, unwanted heating remains a major challenge of Floquet engineering, motivating extensive studies of Floquet thermalization. In this work, we investigate the thermalization of periodically driven many-body systems through the lens of the Krylov chain, and uncover a topological origin of different thermalization behaviors. We show that the zero mode on the Krylov chain corresponds to a particular Floquet effective Hamiltonian with an unfolded spectrum for these driven systems. Furthermore, we demonstrate that when the Krylov chain has a finite band gap and nontrivial band topology, the driven system will thermalize to a finite-temperature state. If the Krylov chain is gapless, it will inevitably lead to infinite-temperature heating. We also reveal that Floquet prethermalization can be understood as the tunneling of a quasi edge mode across a local band gap with local nontrivial topology on the Krylov chain. This perspective provides a systematic route to constructing the effective prethermal Hamiltonian.