Electronic properties of van der Waals materials are highly sensitive to their stacking modes. To explore sliding effects in the two-dimensional (2D) spintronics, we construct a magnetic tunnel junction (MTJ) using sliding bilayer graphene or $h$-BN as barriers and the recently synthesized room-temperature 2D ferromagnet $\mathrm{F}{\mathrm{e}}_3\mathrm{GaT}{\mathrm{e}}_2$ as electrodes. Our ab initio quantum transport simulations with noncollinear framework reveal that layer sliding effectively modulates both the spin transport properties and dynamics of the MTJ. The tunneling magnetoresistance (TMR) reaches $185000\%–230000\%$ (graphene) and $130000\%–200000\%$ ($h$-BN), surpassing theoretically predicted TMR of conventional MgO-based MTJs by two orders of magnitude. Furthermore, the decay rate of the spin-transfer torkance is found to depend on both the degree of slippage and the choice of barrier material, with the maximal spin-transfer torque reaching 230 µeV/V in the bilayer $h$-BN counterpart with AA-stacking mode. Our calculation suggests that sliding is an effective means to fine tune the performance of next-generation 2D spintronic devices.

Identifying superconducting materials with strong electron phonon coupling and high critical temperatures under ambient pressure constitutes a frontier in contemporary condensed matter physics. Here, we report a pioneering investigation of the influence of carrier concentration and phonon softening on superconductivity in the doped diamond and cubic boron nitride (c-BN) system. First-principles calculations indicate that the maximum achievable hole concentrations are $5.0\times {10}^{22}$ and $5.3\times {10}^{22}\mathrm{holes}/{\mathrm{cm}}^3$ for the diamond and c-BN structures, which induce superconducting critical temperatures of 136 and 110 K, respectively. At the maximum theoretically achievable hole concentration, the valence band maximum crosses the Fermi level, forming triply degenerate hole pockets near the $\mathrm{\Gamma }$ point. Flat bands emerge near the Fermi level along the high-symmetry L-W path, and a Van Hove singularity appears at the L point, leading to a pronounced density of states peak at the Fermi level. These carrier features promote softening of the $T_{2g}$ phonon mode at the $\mathrm{\Gamma }$ point, resulting in enhanced phonon coupling strength ${\lambda }_{qv}$ and phonon linewidth ${\gamma }_{qv}$, thereby strengthening the overall electron phonon interaction. These findings provide important theoretical insights into the correlation between carrier concentration and superconducting critical temperatures in conventional superconductors.

Recently, tensor gauge fields and their coupling to fracton phases of matter have attracted more and more research interest, and a series of novel quantum phenomena arising from the coupling has been predicted. Here, we propose a tunable platform using a one-dimensional dipole-conserving Bose-Hubbard chain subject to a periodically driven quadratic potential, which realizes a time-dependent rank-2 electric field. By tuning the drive frequency into resonance with the on-site interaction, the dynamics of dipoles and fractons change drastically from constrained motion to near-ballistic expansion via absorption of a quanta from the tensor electric fields, while the drive amplitude provides a knob for control. We identify experimentally accessible observables: wave packet radius of dipoles and fractons, which quantifies the speed of expansion, and state populations. Our work provides a possible approach to manipulate the dynamics of dipole-conserving quantum systems via tensor gauge fields.

Antiferromagnetic materials with spin splitting have attracted considerable attention for their symmetry-enabled anisotropic spin textures that sustain a zero net magnetization, thereby facilitating efficient spin-current generation. In this work, the highly efficient generation of nonrelativistic spin currents is demonstrated to be facilitated by the distinctive Fermi-surface geometry of X-type collinear antiferromagnets. As a prototype conducting X-type antiferromagnet, the Fermi surface of $\beta \text{−}{\mathrm{Fe}}_2{\mathrm{PO}}_5$ exhibits a distinct $d$-wave altermagnetic characteristic, which compresses into a nearly X-shaped configuration. This results in highly efficient spin currents, achieving a charge-spin conversion efficiency of up to 90%. Moreover, the spin current polarization is controlled by the orientation of the Néel vector. When the Néel vector tilts to the out-of-plane direction, an in-plane injected charge current can generate a special spin current component with both spin polarization and propagation along the out-of-plane direction, whose charge-spin conversion efficiency substantially exceeds that of known ferromagnets, altermagnets, noncollinear antiferromagnets, and low-symmetry materials. The highly efficient charge-spin conversion in X-type antiferromagnets provides a highly effective spin source system for the development of low-power spintronic devices.

The success of a quantum annealing algorithm requires a polynomial scaling of the energy gap. Recently it was shown that a two-dimensional transverse-field Ising model on a square lattice with nearest-neighbor $\pm J$ random coupling has a polynomial energy gap in the symmetric subspace of the parity operator [Nature (London) 631, 749 (2024)], indicating the efficient preparation of its ground states by quantum annealing. However, it is not clear if this result can be generalized to other spin glass models with continuous or biased randomness. Here we prove that under general independent and identical distributions of the exchange energies, the energy gap of a one-dimensional random transverse-field Ising model at the critical point, even without frustration, follows a stretched exponential scaling in the parity-restricted subspace. We discuss the implication of this result to quantum annealing problems.

It was recently reported that heavy-ion irradiation to layered ferromagnetic insulators $\mathrm{Cr}X{\mathrm{Te}}_3$ ($X=\mathrm{Si}$ and Ge) produces amorphous ferromagnetic metals with approximately three times higher transition temperatures ($T_C$) than those of single crystals. This high-$T_C$ metallic state is reminiscent of the correlated metallic phase realized by the Mott transition in single-crystalline $\mathrm{Cr}X{\mathrm{Te}}_3$; however, the detailed mechanism behind this unusual change in the electric and magnetic properties upon amorphization remains elusive. Here, we study the electronic and structural properties of amorphous $\mathrm{Cr}X{\mathrm{Te}}_3$ using transport and optical measurements, as well as x-ray absorption fine structure (XAFS) measurements. In line with the transport dominated by disorder scatterings, bad metallic behavior was observed in the optical conductivity spectra for irradiated samples. The analysis of the extended XAFS oscillations suggests that the basic Cr-Te octahedral structure is likely to remain after amorphization, although distortion and defects are present. As possible mechanisms for the high-$T_C$ amorphous ferromagnetic state, ferromagnetic superexchange interaction is more likely than double-exchange interaction, based on the shrinkage of the charge-transfer gap, local structure change, and change in carrier density.

In this work, we show that suitably designed spatially varying linearly polarized light provides a versatile route to generate and control pseudomagnetic fields in Weyl semimetals through Floquet engineering. Within a high-frequency expansion, we derive an effective axial gauge potential ${\mathit{A}}_5\left(\mathit{r}\right)$ whose curl gives the pseudomagnetic field ${\mathit{B}}_5\left(\mathit{r}\right)$. By mapping the light profile to ${\mathit{A}}_5\left(\mathit{r}\right)$, we establish design principles for pseudomagnetic field textures that mimic strain-induced gauge fields while offering key advantages like dynamic control, full reversibility, spatial selectivity, and absence of material deformation. We compare the Landau-level spectra produced by uniform real and pseudomagnetic fields and also analyze both their linear optical conductivity and the second-order dc responses. Our results enable real-time manipulation of pseudomagnetic fields and predict clear experimental signatures for optically engineered gauge fields in topological semimetals.

We study the robustness of topological ground state degeneracy to long-range interactions in quantum many-body systems. We focus on slowly decaying two-body interactions that scale like a power law $1/r^{\alpha }$ where $\alpha$ is smaller than the spatial dimension; such interactions are beyond the reach of known stability theorems which only apply to short-range or rapidly decaying long-range perturbations. Our main result is a computation of the ground state splitting of several toy models, which are variants of the one-dimensional Ising model $H=-{\sum }_i{\sigma }_i^z{\sigma }_{i+1}^z+\lambda {\sum }_{ij}{|i-j|}^{-\alpha }{\sigma }_i^x{\sigma }_j^x$ with $\lambda >0$ and $\alpha <1$. In one variant, the power-law interactions are replaced by all-to-all interactions $\frac{\lambda }{4L^{\alpha }}{\sum }_{ij}{\sigma }_i^x{\sigma }_j^x$, where $L$ is the system size, while the other variant has true power-law interactions but is built out of quantum rotors rather than Ising spins. These models are also closely connected to the Kitaev $p$-wave wire model with power-law density-density interactions. In these examples, we find that the splitting $\delta$ scales like a stretched exponential $\delta \sim exp(-C{L}^{\frac{1+\alpha }{2}})$. Our computations are based on path integral techniques similar to the instanton method introduced by Coleman. We also study another toy model with long-range interactions that can be analyzed without path integral techniques and that shows similar behavior.

We assess the accuracy of the cumulant expansion (CE) method, combined with the independent-particle approximation (IPA), for calculating charge mobility in electron-phonon systems. As representative testbeds, we consider the Peierls and Fröhlich models, which serve as simplified frameworks where accurate or numerically exact benchmarks are available. These are used to compare the CE results with those obtained using the Boltzmann formalism, the one-shot Migdal approximation, and its self consistent extension—approaches that are presently the most commonly employed alternatives for transport calculations. Supported by analytical arguments based on spectral sum rules and by our previous results for the Holstein model, we argue that, for weak to moderate coupling strengths and not-too-low temperatures, the CE within the IPA framework yields accurate results. In the case of the Peierls model, the role of vertex corrections is also discussed.

Understanding how crystal symmetry governs phonon-phonon scattering is essential for predicting heat transport in two-dimensional semiconductors. While most studies focus on three-phonon (3ph) interactions, growing evidence shows that four-phonon (4ph) processes can be equally important for thermal transport, particularly when phonon scattering is constrained by crystal symmetry beyond energy and momentum conservation. In this work, we investigate the role of out-of-plane reflection symmetry by comparing two phases of monolayer ${\mathrm{HfH}}_2$, which exhibit nearly identical harmonic properties but distinct symmetry. Their large acoustic-optical band gap suppresses scattering channels in which two or three acoustic phonons combine into an optical phonon, thereby enabling a clean isolation of higher-order scattering governed by reflection symmetry. By combining machine-learning interatomic potentials with group theoretical selection-rule analysis, we show that the 1H phase supports symmetry-constrained even-flexural-acoustic (ZA) 4ph channels that greatly enhance higher-order anharmonicity. In contrast, the 1T phase, which lacks out-of-plane reflection symmetry, remains dominated by 3ph scattering with only minor 4ph contributions. As a result, at 300 K the activation of symmetry-constrained channels in the 1H phase reduces the lattice thermal conductivity by more than half and strongly suppresses the ZA-mode contribution. Our work establishes out-of-plane reflection symmetry as a key enabler of strong 4ph scattering and suggests that symmetry engineering may provide a viable route to controlling phonon thermal transport in other two-dimensional transition-metal semiconductors with large acoustic-optical band gaps.

The nonequilibrium Green's function (NEGF) formalism is a powerful tool to study the nonequilibrium dynamics of correlated lattice systems, but its applicability to realistic system sizes and long timescales is limited by unfavorable memory scaling. While compressed representations, such as the recently introduced quantics tensor train (QTT) format, alleviate the memory bottleneck, the efficiency of QTT-NEGF calculations is hindered by poor initializations and slow or unstable convergence of globally updated self-consistent iterations. Here, we introduce a predictor-corrector solver for QTT-NEGF simulations that combines dynamic mode decomposition (DMD) extrapolation with the recently proposed causality-preserving block-time-stepping updates. The DMD predictor supplies accurate initial guesses that reduce the iteration count of the calculation, while the block-time-stepping correction ensures stable convergence even for long propagation intervals. Applying this method to the Hubbard model on a $32\times 32$ lattice within the nonequilibrium $GW$ approximation, we demonstrate stable propagation up to times of $t_{\max }=512$ inverse hoppings, surpassing the capabilities of both matrix-based implementations and previous QTT solvers. Our contribution is twofold. (i) We integrate tensor dynamic mode decomposition with the QTT representation, which establishes a general framework that is not limited to NEGFs. (ii) We demonstrate its practical benefits in NEGF simulations, where it enables stable and efficient access to unprecedented timescales at high momentum resolution, thereby enabling controlled studies of long-time dynamics and nonequilibrium steady states in correlated lattice systems.

Based on first-principles calculations combined with theoretical analysis, we identify a family of monolayer chromium-based group-IV chalcogenides as a new class of two-dimensional (2D) magnetic higher-order topological insulators (HOTIs). Specifically, the $\mathrm{CrC}{X}_3$ ($X=\mathrm{S}$, Se, Te) and ${\mathrm{CrSiS}}_3$ monolayers are found to host conventional antiferromagnetic ground states with $\mathcal{PT}$ symmetry, whereas the Janus compounds ${\mathrm{Cr}}_2{\mathrm{C}}_2{\mathrm{S}}_3{\mathrm{Se}}_3$ and ${\mathrm{Cr}}_2{\mathrm{Si}}_2{\mathrm{S}}_3{\mathrm{Se}}_3$ exhibit altermagnetic ground states. We demonstrate that all these monolayer magnetic materials realize 2D HOTI phases, in which the nontrivial topology is protected by lattice $C_3$ rotational symmetry and manifests as zero-dimensional corner states carrying quantized fractional charges. Moreover, upon inclusion of spin-orbit coupling, these systems remain in the HOTI phase and continue to host robust corner-localized states, confirming the stability of their higher-order topological nature. Our results reveal an intrinsic connection between higher-order topology and magnetic order in 2D antiferromagnetic and altermagnetic systems, identifying chromium-based group-IV chalcogenide monolayers as promising platforms for exploring higher-order topological phases and their potential relevance for future topological and spintronic applications.

Materials with low thermal conductivity effectively reduce heat dissipation, finding significant applications in thermoelectric devices and thermal barrier coatings. We report the low lattice thermal conductivity and high thermoelectric figure-of-merit ($\mathit{ZT}$) of a new ${\mathrm{PbBi}}_2{\mathrm{Te}}_4$ phase. Based on the dual-phonon transport theory, its lattice thermal conductivity is $\sim 0.3\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ (Criterion I) to $\sim 0.4\mathrm{W}{\mathrm{m}}^{-1}{\mathrm{K}}^{-1}$ (Criterion III) at 600 K. Such low lattice thermal conductivity originates from the $s^2$ lone pair electrons residing on both Pb and Bi sites. The presence of double lone pair electrons induces rattling-like vibrations, which intensify phonon scattering and suppress thermal transport. The coexistence of a multiple-valley conduction band and a flat valence band benefits the Seebeck coefficient. The $n$- and $p$-type ${\mathrm{PbBi}}_2{\mathrm{Te}}_4$ compounds exhibit optimal $\mathit{ZT}$ values exceeding or approaching 1.0 at room temperature, rising to $\sim$ 2.01 (Criterion III) to $\sim$ 2.13 (Criterion I) and $\sim$ 1.87 (Criterion III) to $\sim$ 2.01 (Criterion I), respectively, in the intermediate-temperature range. The $n$-type ${\mathrm{PbBi}}_2{\mathrm{Te}}_4$ displays a more pronounced thermoelectric advantage than the $p$-type counterparts. Our findings provide hints for designing new thermoelectric materials with intrinsically low thermal conductivity.

We study a finite-length Kitaev chain coupled to a single mode photonic cavity. The topological phase of the finite-length Kitaev chain is characterized by the presence of fermion parity switching points that correspond to the degeneracy between even and odd parity ground states. Using exact diagonalization, we compute the many-body energy spectrum of the electron-photon Hamiltonian and we find that the ground state in the topological phase of the Kitaev chain is only weakly affected by the cavity coupling. This is in contrast with the excited states showing strong dependence on the cavity frequency. We find that the photon number and the photonic field quadratures peak at values of the chemical potential corresponding to parity switching points revealing a property of the finite-length Kitaev chain in the topological phase. This later finding suggests that quantum optics experiments could be used to detect topological features of the Kitaev chain embedded into a photonic cavity. Moreover, calculations of photonic quadratures reveal squeezed states that are both captured by the exact diagonalization technique and mean-field decoupling. However, the mean-field approach fails to correctly capture the photonic probability in the odd photonic states.

The momentum dependence of Rashba spin-orbit coupling (RSOC) is a key ingredient for engineering topological superconductors (TSCs), yet research has overwhelmingly focused on its linear-in-momentum form. This focus has restricted time-reversal invariant TSCs to helical $p$-wave states, which are characterized by a ${\mathbb{Z}}_2$ topological invariant that permits at most a single Majorana Kramers pair at a given boundary. Their existence has also been tied to the stringent criterion of an odd number of Fermi surfaces (FSs). In this work, we establish higher-order RSOC as a powerful design principle to go beyond the ${\mathbb{Z}}_2$ classification and the odd-FS criterion. We demonstrate that a bilayer system with a pure cubic RSOC and an intrinsic odd-parity pairing on a single FS yields a rare 2D helical $f$ wave TSC. This state is characterized by a large mirror Chern number (MCN) of ${\mathcal{N}}_{\text{M}}=3$ and hosts three Kramers pairs of Majorana edge modes. Remarkably, the interplay of linear and cubic RSOCs in this bilayer can generate a helical hybrid $p+f$-wave TSC with an even larger MCN of ${\mathcal{N}}_{\text{M}}=4$ from a normal state with two FSs, thereby circumventing the conventional odd-FS criterion. Our work establishes higher-order RSOC as a “topology multiplier” for realizing TSCs with multiple Majorana Kramers channels, fundamentally reshapes the criteria for helical TSCs, and holds immediate relevance for tunable platforms like oxide heterostructures.

The coexistence of topological magnons and electrons in magnetic materials presents a compelling route toward developing low-dissipation, multifunctional spintronic devices. However, material systems enabling their simultaneous realization and control remain largely unexplored. Here, we propose the coexistence and concurrent tunability of magnonic and electronic Chern insulator phases in Kitaev magnets and use ${\mathrm{MnBr}}_3$ monolayer as a prototype. We find the significant Kitaev interaction in ${\mathrm{MnBr}}_3$ induces the magnonic Chern insulator phase, manifesting as the magnon thermal Hall effect. Concurrently, ${\mathrm{MnBr}}_3$ exhibits the quantum anomalous Hall effect driven by its electronic Chern insulator phase. Crucially, we demonstrate that these dual topological phases can be simultaneously controlled by reorienting the in-plane spins with an external magnetic field. Our findings not only deepen the fundamental understanding of spin excitations in Kitaev magnets but also provide a promising platform for exploring the interplay between electronic and magnonic topology.

Nonvolatile manipulation of magnetic orderings in two-dimensional (2D) van der Waals (vdW) materials presents a promising avenue for advanced spintronic applications. Bilayer ${\mathrm{CrI}}_3$ (BL-${\mathrm{CrI}}_3$) exhibits an interlayer antiferromagnetic (AFM) ground state, distinct from the interlayer ferromagnetic (FM) ordering of its bulk counterpart, making it a compelling system for studying the magnetic phase transition. While integrating BL-${\mathrm{CrI}}_3$ with a ferroelectric layer like $\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ has been proposed as a strategy to modulate these transitions, prior computational studies have yielded conflicting results. Here, we systematically investigate BL-${\mathrm{CrI}}_3/\alpha \text{−}{\mathrm{In}}_2{\mathrm{Se}}_3$ heterostructures using first-principles calculations, examining the effects of lattice strain, spin-orbit coupling (SOC), and electric polarization on magnetic stability. Our findings reveal that larger in-plane lattice constants favor the AFM state, while SOC promotes FM ordering. Notably, a bilayer ${\mathrm{In}}_2{\mathrm{Se}}_3$ substrate proves highly effective in achieving nonvolatile magnetic ground-state reversal. These results decipher the critical roles of strain, SOC and electric polarization in the manipulation of magnetism in 2D materials and provide essential insights for designing 2D vdW heterostructures with robust magnetoelectric properties.

The miniaturization of superconducting electronics demands precise control over quasiparticle dynamics at the nanoscale. Understanding and controlling quasiparticle dynamics is essential for advancing superconducting electronics, particularly as device dimensions approach the nanoscale. Here we present direct experimental evidence for the quasiparticle-to-supercurrent conversion in planar SN-N-NS Josephson nanobridges with submicron electrodes. By employing a versatile measurement platform, we demonstrate that the geometry of injection through superconducting or normal-metal leads significantly alters the critical current and junction resistance. Using a tunable measurement setup that allows current injection through either superconducting or normal-metal leads, we uncover marked changes in critical current and resistance depending on the injection geometry. These effects become significant when electrode widths fall below the characteristic conversion length of $\sim 400\mathrm{nm}$. These observations are quantitatively explained by a phenomenological model that accounts for nonequilibrium transport and incomplete quasiparticle conversion in narrow electrodes. These results point to the emergence of nonequilibrium transport governed by an intrinsic conversion length. We develop and apply a method for extracting this length from standard transport measurements, offering a practical diagnostic for nanoscale superconducting circuits. Our work establishes fundamental design rules for minimizing energy dissipation and optimizing performance in superconducting quantum devices. Our findings enable optimized design of compact Josephson junctions and support the integration of proximity-based weak links into scalable superconducting logic and sensing architectures.

Josephson diode (JD) effect in Josephson tunnel junctions (JTJs) has attracted a great deal of attention due to its importance for developing superconducting-circuitry-based quantum technologies. Even though the preparation of high-quality JTJs by techniques employed in the semiconductor industry has been demonstrated, which was an important milestone because JTJs are the building blocks of superconducting electronics even before the quantum era, the JD effect has not been accomplished in them, nor has the highly desirable electrical control of the effect. We report here the fabrication of JTJs featuring a composite tunnel barrier of ${\mathrm{Al}}_2{\mathrm{O}}_3$ and ${\mathrm{Hf}}_{0.8}{\mathrm{Zr}}_{0.2}{\mathrm{O}}_2$ using complementary-metal-oxide-semiconductor compatible atomic layer deposition. These JTJs were found to show the JD effect in nominally zero magnetic fields with nonreciprocity controllable via an electric training current, yielding a surprisingly large diode efficiency. The quasiparticle tunneling, through which the Josephson coupling in a JTJ is established, was found to show theoretically expected gap features but no nonreciprocity. We attribute these observations to the simultaneous presence of positive and negative local Josephson couplings in the JTJs, with the negative Josephson coupling originating from indirect tunneling, which results in spontaneous time-reversal symmetry breaking. The double-minima washboard potential for the ensemble-averaged phase difference in the resistively and capacitively shunted junction model is shown to fully account for the experimentally observed JD effect.