Switching of perpendicular magnetization by spin-orbit torque underpins the next-generation spintronic technologies, particularly for nonvolatile, ultrafast, and energy-efficient data storage devices. However, the technology has been facing two major challenges, the necessity of a bias magnetic field and the very high switching current density of about ${10}^6-{10}^7\mathrm{A}\mathrm{c}{\mathrm{m}}^{-2}$, which lead to complex device structure, reduced lifetime and high energy consumption. Here, we demonstrate highly efficient field-free switching of perpendicular magnetization with ultra-low current at room temperature using ${\mathrm{Fe}}_3{\mathrm{GaTe}}_2/{\mathrm{WTe}}_2/{\mathrm{CuO}}_{\mathrm{x}}$ heterostructures. The out-of-plane anti-damping torque generated by the ultrathin ${\mathrm{WTe}}_2$ layer eliminates the need for a bias magnetic field. And the significantly enhanced spin current originating from the ${\mathrm{WTe}}_2/{\mathrm{CuO}}_{\mathrm{x}}$ interface leads to a ultra-low switching current density of merely $3.6\times {10}^5\mathrm{A}\mathrm{c}{\mathrm{m}}^{-2}$, significantly lower than the lowest reported value. These findings open a new paradigm in the design of all-electric, low-power spintronic devices.

We investigate the monitored dynamics of many-body quantum systems in which projective measurements of extensive operators are alternated with unitary evolution. Focusing on mean-field models characterized by all-to-all interactions, we develop a general framework that captures the thermodynamic limit, where a semiclassical description naturally emerges. Remarkably, we uncover novel stationary states, distinct from the conventional infinite-temperature state, that arise upon taking the infinite-volume limit. Counterintuitively, this phenomenon is not linked to the closing of the Lindbladian gap in that limit. We provide an analytical explanation for this unexpected behavior.

The interplay between real and reciprocal space topology yields intrinsically linked transport phenomena in topological magnetic material systems. In particular, broken time-reversal symmetry together with strong Dzyaloshinskii-Moriya interaction and pronounced uniaxial anisotropy can simultaneously stabilize momentum-space Berry-curvature singularities (Weyl nodes) and real-space chiral spin textures. The concurrent realization of these dual topological features remains exceptionally rare, particularly in epitaxial thin films. Here, we present a combined first-principles and detailed magnetotransport investigation of epitaxial $\mathrm{F}{\mathrm{e}}_5\mathrm{S}{\mathrm{i}}_3$ thin films, establishing the material as a magnetic Weyl nodal-line metal in which density functional theory (DFT) calculations uncover a topologically nontrivial electronic structure featuring six pairs of Weyl nodes near the Fermi level ($E_{\mathrm{F}}$) and pronounced Berry-curvature hot spots at high-symmetry points, and accompanied by a large topological Hall response. High-quality epitaxial films exhibit robust ferromagnetism with a high Curie temperature ($T_{\mathrm{C}}$) of approximately 370 K and strong magnetocrystalline anisotropy. The magnetotransport measurements on epitaxial films reveal the corresponding Berry-curvature-driven responses, including a significantly large intrinsic anomalous Hall conductivity of 504 S/cm and a high anomalous Hall angle of 5.5%, which is in good agreement with DFT calculations. Furthermore, a substantial topological Hall resistivity of $1.6\mu \mathrm{\Omega }\mathrm{cm}$ is robust across a wide temperature range, indicating the possibility of robust chiral spin textures in the thin-film geometry. These combined theoretical and experimental results establish $\mathrm{F}{\mathrm{e}}_5\mathrm{S}{\mathrm{i}}_3$ as a unique, low-cost, centrosymmetric magnetic Weyl nodal-line material, providing a versatile platform for exploring coupled real- and reciprocal-space topologies in topological spintronic applications.

${\mathrm{TaSb}}_2$, a member of the ${\mathrm{TmPn}}_2$ family of materials, hosts the very rare dual topological phase—weak topological insulating state and topological crystalline insulating state along different crystallographic orientations. So far, studies on the electronic structure of ${\mathrm{TmPn}}_2$ compounds have focused on their overall electronic structure and the bulk open-orbit Fermi surfaces. Using angle-resolved photoemission spectroscopy, density functional theory calculations, and transport measurements, we distinguish the intertwined bulk and surface states on the weakly topological $\left(20\overline{1}\right)$ plane of ${\mathrm{TaSb}}_2$. We identify multiple electron- and holelike bulk bands, yielding a near-perfect carrier compensation. Crucially, we observe open-orbit FSs near $\overline{M}$ and parallel to $\overline{\mathrm{\Gamma }}-\overline{Y}$ direction that are entirely of surface origin. The surface states also exhibit band crossing at $\sim 0.6\mathrm{eV}$ below Fermi level at the time-reversal invariant momentum $\overline{M}$, indicating nontrivial band topology. Consistent with this, magnetotransport measurements display weak antilocalization, establishing ${\mathrm{TaSb}}_2$ as a platform for spin-polarized topological transport on a weakly topological surface.

We investigated the quantum size effect (QSE) in bimetallic ${\mathrm{Pt}}_{1-x}{\mathrm{Pd}}_x$ and ${\mathrm{Pt}}_{1-x}{\mathrm{Ni}}_x$ nanoparticles, using ${}^{195}\mathrm{Pt}$ nuclear magnetic resonance measurements. The temperature and size dependencies of the anomaly in the nuclear spin-lattice relaxation rate divided by temperature $1/T_{1}T$ in the ${\mathrm{Pt}}_{1-x}{\mathrm{Pd}}_x$ nanoparticles suggest similar electron states between Pt and Pd atoms and are well understood by the QSE. The temperature and composition variations of $1/T_{1}T$ and the Knight shift reveal a systematic increase in the density of states and a reduction of the characteristic energy scale $T^{*}$ with increasing Ni content, consistent with the Kubo gap ${\delta }_{\mathrm{Kubo}}$. In contrast to the ${\mathrm{Pt}}_{1-x}{\mathrm{Cu}}_x$ nanoparticles where the QSE is suppressed, the ${\mathrm{Pt}}_{1-x}{\mathrm{Ni}}_x$ nanoparticles exhibit clear signatures of quantum energy discretization. This discrepancy highlights the essential role of $d$ electrons in the manifestation of the QSE. Furthermore, analysis of the modified Korringa parameter $K\left(\alpha \right)$ suggests enhanced ferromagnetic correlations with increasing Ni concentration, approaching a ferromagnetic quantum critical regime. These results provide experimental evidence that $d$-electron density of states plays a crucial role in the manifestation of the QSE in the nanoparticles formed by the metallic $d$-electron atoms.

Scalar spin chirality (SSC), whose nonzero value $\langle {\mathbf{S}}_i·({\mathbf{S}}_j\times {\mathbf{S}}_k)\rangle \ne 0$ implies the breaking of time-reversal and certain point-group symmetries in the ground state, is a key quantity characterizing chiral magnetism in both classical and quantum settings. Classical SSC is manifested, for instance, in the skyrmion crystal phase, while quantum SSC is still highly sought after in various frustrated spin-1/2 models. An interesting possibility that has not been explored so far is the case in which SSC is symmetrywise allowed, yet remains zero classically due to the collinear or coplanar arrangement of spins, but is generated by virtue of quantum fluctuation. We demonstrate the existence of precisely such a phase in a spin-1/2 triangular-lattice model with XXZ interaction, spin-orbit-induced exchange interactions, and an external magnetic field. Using the infinite density matrix renormalization group (iDMRG) method, we thoroughly map out the phase diagram of the model and identify several phases with coexisting magnetic order and SSC. Nonzero SSC arises despite the classical magnetic order being collinear or coplanar. We provide detailed magnon analysis to ascribe its origin to quantum fluctuations around classical magnetic order. The magnon analysis reproduces the sign and characteristic magnitude of the iDMRG SSC and identifies its microscopic origin in quantum fluctuations. We map out the magnon spectrum and its Berry curvature, culminating in the prediction of finite thermal Hall conductivity in these phases with SSC.

We investigate the coherent exciton spin dynamics in a single InAlAs/AlGaAs quantum dot using time-resolved quantum state tomography. Under two-longitudinal-optical (LO)-phonon quasiresonant excitation of neutral exciton, we observe pronounced quantum beats in the circular and diagonal polarization components, reflecting the fine-structure splitting ($\mathrm{\Delta }\approx 19.6\mu \text{eV}$). By employing a global fitting procedure across three orthogonal polarization bases, we demonstrate that the spin evolution is consistently described by a unified Hamiltonian dominated by the anisotropic exchange interaction. While the initial degree of circular polarization is limited to $\approx 0.28$ due to fast relaxation processes during carrier cooling, the subsequent dynamics reveal a long-lived spin coherence ($1.1\pm 0.2\mathrm{ns}$) that exceeds the exciton lifetime ($\sim 767$ ps). Our analysis indicates that the buildup of the exciton spin polarization exhibits no resolvable delay relative to the exciton population dynamics within the experimental time resolution. In addition, no discernible Overhauser shift was observed within the present signal-to-noise limit, suggesting a negligible influence of the local nuclear environment under the present experimental conditions. These results provide a quantitative benchmark for the three-dimensional spin-state reconstruction using differential polarization signals, demonstrating the feasibility of using quasiresonant excitation for stable spin initialization in semiconductor nanostructures.

One of the most powerful strategies to address properties of real many-body systems is to incorporate data obtained for models, for example, to use data of the homogeneous electron gas in order to build the local density approximation for the Kohn-Sham exchange-correlation potential. In the present work, we examine to what extent we can use model data to design functionals directly for observables of materials. In particular, we study different approximations for the charge density of real inhomogeneous materials expressed as a simple, explicit functional of a given Kohn-Sham potential, using as a central building block the Lindhard density-density response function of the homogeneous electron gas. Our increasingly realistic set of approximations includes a fully nearsighted expression equivalent to the Thomas-Fermi approximation, functional Taylor expansions, and different approximations to the connector theory developed by A. Aouina et al. [npj Comput. Mater. 11, 242 (2025)]. In all cases, the charge density is obtained without ever solving the Kohn-Sham Schrödinger equation. Results for cubic helium, a prototypical strongly inhomogeneous material, as well as the covalent semiconductor silicon and metallic aluminum, systematically improve with higher levels of approximation. At the present stage, the results may be used for qualitative discussions or as an optimized starting point for a self-consistent Kohn-Sham cycle. More generally, their quality indicates that this is a promising route to obtain functional expressions for observables that are relatively simple to calculate and to analyze.

Fluorite ferroelectrics such as hafnia defy our understanding of ferroelectricity, even with regard to the intrinsic properties of ideal crystals. Here, we focus on a critical puzzle: the sign of the electric polarization. Using first-principles simulations, we show that a polar hafnia layer with a fixed atomic configuration can give rise to depolarizing fields of either positive or negative sign, depending on the environment. This implies that the polarization of bulk hafnia is not well defined, thus being extrinsic in nature. We explain this result and discuss its relevance to other ferroelectric families.

The non-Hermitian skin effect describes the phenomenon of exponential localization of single-particle eigenstates near the boundary of the system. We consider its generalization to the many-body regime by investigating a general class of interacting fermion lattice models in Markovian open quantum systems. Therein, the elementary excitations from the “vacuum” (steady state) are given by two types of dissipative fermionic modes composed of single-fermion operators, which govern the long-time nonequilibrium dynamics. We perturbatively calculate the self-energy matrix of these bare modes in the presence of interactions, and utilize the non-Bloch band theory to derive an exact integral representation. By imposing complex momentum conservation, we obtain a simplified expression for corrections to Liouvillian spectrum that agrees well with numerical calculations to high precision. We further perform perturbative analysis of Liouvillian eigenstates and identify signatures of interaction-enhanced NHSE at the quasiparticle level, manifested as renormalization of the generalized Brillouin zone. Our results establish a diagrammatic framework for dissipative interacting fermions with non-Hermitian skin effect in a description of full-fledged Lindblad master equations, which resembles Fermi liquid theory in terms of interaction-dressed quasiparticles.

Nonlinear Hall effects provide a powerful probe of quantum geometry in solids and enable rectification phenomena beyond the constraints of linear response. In this Letter, we predict a layer nonlinear Hall effect (LNHE) in stacked bilayer systems composed of nonmagnetic or antiferromagnetic materials with a vanishing linear Hall conductivity. In such systems, the second- or third-order nonlinear Hall responses are intrinsically layer odd: the contributions from the two constituent layers have equal magnitude but opposite sign, resulting in exact cancellation under layer-exchange symmetry. An out-of-plane electric field $E_z$ can break this symmetry, thereby unveiling the hidden response and converting it into a switchable macroscopic nonlinear Hall signal. Using a minimal $k·p$ model, we demonstrate that the LNHE can originate from the Berry curvature dipole mechanism. A systematic symmetry analysis of all 80 layer groups further yields a complete classification of the symmetry constraints and stacking configurations that allow for this type of LNHE. Beyond this mechanism, additional symmetry analysis reveals that LNHE may also arise from quantum metric dipole or inversed mass dipole. Remarkably, even in cases where second-order nonlinear Hall responses are symmetry forbidden, a third-order LNHE can still survive in certain stacked bilayer configurations. First-principles calculations on representative bilayers—nonmagnetic $1{\mathrm{T}}^{\prime }\text{−}{\mathrm{WTe}}_2$ and $1{\mathrm{T}}^{\prime }\text{−}{\mathrm{ReS}}_2$—explicitly demonstrate electrically reversible second-order LNHE, in full agreement with our symmetry-based predictions. Overall, our results establish LNHE as a universal phenomenon in a wide range of layered quantum materials and provide a robust route toward electrically tunable nonlinear transport.

Critical non-Hermitian phenomena constitute a hallmark of non-Hermitian systems, characterized by discontinuous jumping of the bulk states across a critical parameter point in the thermodynamic limit. Recently, theoretical studies have predicted a novel critical phenomenon associated with edge states, termed critical non-Hermitian edge states, which has not yet been verified experimentally. Here, we realize a one-dimensional electric circuit and demonstrate the existence of critical non-Hermitian edge states. In the thermodynamic limit, the eigenvectors of two edge states collapse into an exceptional point when the onsite capacitance is absent, whereas even an infinitesimal capacitance renders them nearly orthogonal. This critical non-Hermitian phenomenon is observed by measuring the distributions of admittance eigenvectors. Our experimental results reveal a unique type of critical non-Hermitian phenomenon and further enrich experimental non-Hermitian physics.

Point defects in two-dimensional (2D) oxides can simultaneously generate magnetic and polar responses, but the microscopic origin and periodic supercell effects remain elusive. Herein, we take ${\mathrm{ZrMo}}_2{\mathrm{O}}_8$ monolayer as a prototypical 2D oxide to investigate terminal oxygen vacancies via first-principles calculations to elucidate these puzzles. In this system, a neutral terminal oxygen vacancy forms a magnetopolar defect unit with a $2{\mu }_{\mathrm{B}}$ local moment, an out-of-plane dipole, and easy-axis anisotropy. The defect induces two in-gap states: a deep Mo-centered state hosting the magnetic core, and a shallower, bridge-active state extending toward ligands. For vacancy pairs, the supercell energy splitting $\mathrm{\Delta }E$ is governed by the retained Mo-O-Zr-O-Mo connectivity rather than nominal separation and becomes numerically unresolved only after all candidate pathways are removed within the tested supercell family. These results demonstrate that a single vacancy-driven reconstruction accounts for both magnetic and polar features, remains robust over the tested vacancy-concentration range, and highlights the critical role of connectivity in interpreting defect-pair interactions. This state-resolved and connectivity-aware framework provides microscopic insight for analyzing magnetopolar defects in low-dimensional oxides with material-specific vacancy chemistry.

We map the complete classical phase diagram of the spin Hamiltonian describing pyrochlore rare-earth magnets with all symmetry-allowed nearest-neighbor bond-dependent anisotropic two-spin interactions. We provide a simple derivation of the organization of spins into tensor degrees of freedom describing the multipole moments of a tetrahedron, whose components correspond to irreducible representations (irreps) of the tetrahedral symmetry group $T_d$. By parametrizing the Hamiltonian directly in terms of the energies of the individual irreps, we perform an exhaustive search of all possible irrep degeneracies (collisions) which may host stable classical spin liquids arising at classical multicritical points. We find four one-parameter families of models along which three phases are degenerate, all four of which merge at the Heisenberg antiferromagnetic point and its dual, and we give a complete three-dimensional picture of the phase diagram showing all of the phases and their intersections. The appearance of two copies of a single irrep implies an extra degenerate locus which pierces the phase boundaries at special points, yielding two additional isolated triple points. We demonstrate that one-parameter families of Hamiltonians are characterized by a topological invariant describing how the ground-state spin configuration winds when adiabatically transported around this degenerate locus, analogous to a diabolical locus in quantum field theory. We provide a comprehensive catalog of all flat-band degeneracies in the phase diagram and discuss the mechanisms that may allow for or impede the realization of a variety of classical spin liquids described by tensor gauge fields exhibiting nodal line singularities and concomitant multifold pinch points. Last, we provide a list of all cases where three irreps are degenerate above the ground state, which may lead to interesting features in the spin wave spectrum within each ordered phase.

We report carbon doping modulation of interface magnetic anisotropy and Dzyaloshinskii-Moriya (DM) interaction in the Co/Pt multilayers with different Co sublayer thicknesses. A doping-driven spin reorientation transition (SRT) in Co/Pt multilayers was demonstrated. The separation of bulk and interface magnetic anisotropy revealed that the carbon doping preferentially disrupted the Co/Pt interface. The existence of DM interaction is confirmed by the anomalous Hall effect and Brillouin light scattering spectroscopy measurements. The competition between the perpendicular magnetic anisotropy and the DM interaction induces the domain transition from droplet to dendritic domain, which is observed by a polar magneto-optical Kerr effect microscope and reproduced by micromagnetic simulations with material-specific parameters. First-principles calculations are used to understand the doping-driven SRT. The lattice volume variation of the Co sublayer and the increase of average interlayer spacing $d$ are responsible for the bulk and interface magnetic anisotropy reduction, respectively. This work establishes doping with metalloid elements as an effective approach for significant modulating magnetism in multilayers and provides insights for designing potential spintronic materials via doping-engineered magnetic properties.

The orbital Hall effect (OHE) has attracted intensive studies recently due to its potential for substantially enhancing spin-orbit torque (SOT) generation, which is essential for the SOT-induced magnetization switching in spintronic devices. In this work, we report highly efficient SOT-driven magnetization switching in nonmagnet (NM)/CoPt bilayers, enabled by a pronounced OHE in NM and substantial orbital-to-spin conversion within the CoPt ferromagnet. The critical current density for the magnetization switching in a Ti/CoPt device is reduced by an order of magnitude compared to that in a CoPt single layer. Correspondingly, SOT efficiency measurements reveal an enhancement by one order of magnitude in Ti/CoPt relative to CoPt alone. This enhancement is attributed to the large OHE in Ti rather than its negligible spin Hall effect. The orbital current generated in Ti is injected into CoPt and then converted into spin current via strong spin-orbit coupling in CoPt. Our findings pave the way for leveraging orbital current to further amplify the efficiency of magnetization switching in spintronic devices.

Unconventional superconductivity (SC) featuring multifermion orderings has attracted significant attention. However, previous studies have primarily focused on two-dimensional (2D) systems or 3D systems with effective 2D symmetries. Here, we explore the vestigial phases arising from thermal fluctuations of chiral SC in 3D systems governed by the cubic $O_h$ point group. By constructing low-energy effective Hamiltonians via Ginzburg-Landau analysis and conducting Monte Carlo simulations, we systematically analyze the phase fluctuations of chiral orders within the $E_g$ and $T_{2g}/T_{1u}$ irreducible representations (IRRPs). We identify a phase diagram topology distinct from its 2D counterparts, where the multiphase intersection manifests as a tetracritical point rather than the triple point typically found in 2D systems. Our findings reveal that, for both the $E_g$ and $T_{2g}/T_{1u}$ IRRPs, the primary chiral orders melt into a chiral metallic phase within specific parameter regimes. Furthermore, for the $E_g$ IRRP, phase fluctuations induce a charge-$4e$ phase, while for the $T_{2g}$ and $T_{1u}$ IRRPs, they lead to a higher-order charge-$6e$ SC state. Ultimately, our work highlights the role of nontrivial 3D crystalline symmetries in driving exotic vestigial orders.

The anomalously high fluorine ionic diffusivity reported in ${\mathrm{CaF}}_2\text{−}{\mathrm{BaF}}_2$ multilayer ultrathin heterostructures at around 600 K more than two decades ago [N. Sata et al., Nature (London) 408, 946 (2000)] has remained unresolved due to the complex distribution and diffusion behavior of vacancies and interstitials at the interface. Here, we address this long-standing issue by employing a cluster expansion model combined with machine-learning molecular dynamics, enabling atomic-level analysis of fluorine ion thermodynamics and kinetics. We find that fluorine vacancies preferentially accumulate at the ${\mathrm{CaF}}_2$-side interface, whereas fluorine interstitials appear only on the ${\mathrm{BaF}}_2$ side. At 600 K, diffusion is dominated by interstitial-mediated fluorine diffusion in the ${\mathrm{BaF}}_2$ region, whereas at 900 K vacancy-mediated fluorine diffusion on the ${\mathrm{CaF}}_2$ side becomes active, and the coexistence of both mechanisms leads to a synergistic enhancement of the overall diffusivity. The spatial separation of defect distributions and diffusion pathways arises from the coupling between electronic stabilization and asymmetric interfacial strain. Electron pairing between trapped electrons in adjacent ${\mathrm{V}}_{\mathrm{F}}\mathrm{s}$ stabilizes ${\mathrm{V}}_{\mathrm{F}}$ clustering at the ${\mathrm{CaF}}_2$-side interface, whereas tensile strain on the ${\mathrm{BaF}}_2$ side enlarges octahedral interstitial sites and promotes interstitial-mediated fluorine hopping; conversely, compressive strain on the ${\mathrm{CaF}}_2$ side suppresses interstitial occupation. These findings provide microscopic insight into the origin of the anomalous diffusion and clarify how electronic stabilization of vacancy clustering and local strain modulation of interstitial formation jointly regulate defect distributions and diffusion mechanisms in fluorite-structured heterostructures.

The utilization of terahertz (THz) emission spectroscopy in femtosecond photoexcited spintronic heterostructures has emerged as a versatile tool for investigating ultrafast spin transport in a noncontact and noninvasive manner. However, the investigation of ultrafast orbital transport is still in the primitive stage. Here, we experimentally demonstrate the orbital-to-charge current conversion in Co/Ru heterostructures and identify signatures that cannot be consistently explained within a conventional spin-current framework. Time-domain measurements reveal delayed and broadened THz waveforms with increasing Ru thickness, suggesting the presence of long-range angular momentum transport associated with orbital contributions. In Co/Pt/Ru trilayers, the THz emission is further enhanced through cooperative effects between the inverse spin Hall effect (ISHE) in Pt and inverse orbital Hall effect (IOHE) in Ru, where collinear charge currents are generated and add constructively. In contrast, reversed stacking configurations exhibit suppressed emission, highlighting the critical role of stacking sequence and interface-controlled transmission. Ferromagnetic resonance (FMR) measurements reveal a strong correlation between damping and THz amplitude, highlighting efficient angular momentum conversion. These results position Co/Ru as a promising orbitronic platform for tunable ultrafast THz emission. Our results not only strengthen the physical mechanism of condensed matter physics but also pave the way for designing promising spin-orbitronic devices and THz emitters.