The quantum anomalous Hall (QAH) effect is usually realized through ferromagnetism or magnetic doping, which limits material choices and often results in low mobility, disorder sensitivity, and low operating temperatures. Here, we propose a mechanism to achieve the QAH phase without net magnetization, using altermagnetic exchange on a weak topological insulator (WTI). The altermagnetic order selectively gaps the Dirac cone at the $Z$ point, while hybridization between the top and bottom surfaces of the WTI thin film opens a trivial gap at the $\mathrm{\Gamma }$ point, generating a Chern number $\mathcal{C}=1$ phase with a single chiral edge channel. We verify the topological transition through both a minimal thin-film model and a slab geometry, and compute the associated Hall response. As altermagnets and layered WTIs already exist experimentally, this mechanism offers a promising and experimentally accessible route to realizing QAH phases without magnetic doping or global magnetization. The results indicate that altermagnetic surface engineering may provide a clean and controllable pathway for realizing dissipationless edge transport in layered quantum materials.

We study the local density of states (LDOS) distribution of a general class of weighted Erdős-Rényi graphs. Using the cavity method, we obtain a good approximation to the full LDOS distribution and compact expressions for its power-law tails, which we show to have exponent 3 in the extended phase. We deduce that the eigenvectors in the continuous part of the spectrum are extended but (weakly) multifractal, and we extract expressions for the associated fractal dimensions and the singularity spectrum. We also demonstrate that the inverse participation ratio in this multifractal phase exhibits an unusual logarithmic scaling with system size, which is neither fully extended nor localized by the usual definitions. Finally, we verify that some symmetry properties (derived from the nonlinear sigma model), which have been shown to hold for many systems exhibiting multifractality, also hold in our case, both for the LDOS distribution and the singularity spectrum.

A transition from crystal-field to spin wave excitations has been experimentally observed in ${\mathrm{PrFeO}}_3$ using inelastic neutron scattering. Theoretical modeling with density functional theory and the mean field random phase approximation successfully reproduces the experimental observations and allows extraction of the values for the various exchange interactions. The study reveals that the strong coupling between the two magnetic sublattices of Pr and Fe is the fundamental mechanism underlying the low-temperature Pr magnetism. This coupling, analogous to the Dicke cooperative interaction between atoms and photons, polarizes the Pr moments, enhances the Pr-Pr interactions, and contributes to the formation of a quasidoublet, leading to the transition from single-particle to collective excitations within the Pr sublattice. Furthermore, this coupling induces spin reorientation on the Fe sublattice. The manipulation of magnetic moments via spin waves is achievable through the coupling between different magnetic sublattices in a bulk material containing multiple magnetic ions.

We present the global topological phase diagram of a two-dimensional electron gas placed in a quantizing magnetic field and proximitized by a superconducting vortex lattice. Our theory allows for arbitrary ratios of the pairing amplitude, magnetic field, and chemical potential. By analyzing the Bogoliubov-de Gennes Hamiltonian, we show that the resulting phase diagram is highly nontrivial, featuring a plethora of topological superconducting phases with chiral edge modes of quasiparticles. Landau-level mixing plays an essential role in our theory: Even in the weak-pairing limit, it generically splits the integer quantum Hall transition lines into a sequence of transitions with larger Chern number jumps of both signs protected by the symmetries of the superconducting vortex lattice. Interestingly, we find that weak pairing induces trivial or topological superconductivity when chemical potential is tuned to a Landau-level energy, depending on the Landau-level index.

Triangular-lattice rare-earth chalcogenides $\mathrm{NaYb}{X}_2$ ($X$ = O, S, and Se) are promising quantum spin liquid (QSL) candidates, while the exact properties of the quantum state remain elusive. In this work, we present a spin-dynamic investigation of ${\mathrm{NaYbSe}}_2$. Magnetic susceptibility and specific heat reveal pronounced easy-plane anisotropy and short-range spin correlations below 20 K. In the $X$-band and pulsed high-field electron spin resonance (ESR) measurements, the temperature dependence of anisotropic $g$ factors and linewidths illustrate the development of spin correlations at low temperatures. Interestingly, unlike the noninteracting paramagnets showing linear frequency-field (ν-$H$) behavior through the origin, ${\mathrm{NaYbSe}}_2$ at 2 K exhibits complex dynamical characteristics: The resonance mode evolves from low-field linear ν-$H$ behavior to an easy-plane antiferromagnetic-like (AFM-like) resonance with a gap of 21.06(2) GHz in the intermediate fields and finally reverts to a high-field linear ν-$H$ dependence as the system approaches the magnetic saturation. This phenomenon indicates the suppression of quantum fluctuations by a strong magnetic field, facilitating magnetic-field-induced ordering. Through fitting with the easy-plane AFM-like resonance model, we extracted an effective exchange interaction of $J$ = −1.18 (2) K for ${\mathrm{NaYbSe}}_2$. The ν-$H$ relationship in ESR measurements provides insight for understanding unconventional spin excitations in QSLs of triangular-lattice quantum magnets.

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.