Kitaev materials are of great interest due to their potential in realizing quantum spin liquid (QSL) states and applications in topological quantum computing. In the pursuit of realizing Kitaev QSL, a Mott insulator with strong bond-dependent frustration and weak geometric frustration is highly desirable. Here we explore Kitaev physics in the van der Waals triangular antiferromagnet (AF) ${\mathrm{CoI}}_2$, through the spin-orbital states and Wannier function analyses, exact diagonalization and density matrix renormalization group study of the electronic structure and magnetic properties. We find that the high-spin ${\mathrm{Co}}^{2+}$ ion is in the $J_{\mathrm{eff}}=1/2$ state because of strong spin-orbit coupling, and the weak trigonal elongation and crystal field contribute to the observed weak in-plane magnetic anisotropy. The strong $t_{2g}\text{−}{e}_g$ hopping via the strong Co $3d$-I $5p$ hybridization gives rise to a strong Kitaev interaction ($K_1$) at the first nearest neighbors (1NN), and the long Co-Co distance and the weak $t_{2g}\text{−}{t}_{2g}$ hoppings determine a weak Heisenberg interaction $J_1$. The resultant $|K_1/J_1|$ = 6.63 confirms a strong bond-dependent frustration, while the geometric frustration due to the 3NN Heisenberg interaction $J_3$ gets involved, and they all together result in the experimental helical AF order in ${\mathrm{CoI}}_2$. We then propose to suppress the $J_3$ using a partial Mg substitution for Co, and indeed we find that ${\mathrm{Co}}_{2/3}{\mathrm{Mg}}_{1/3}{\mathrm{I}}_2$ has the much reduced geometric frustration but hosts the robust bond-dependent frustration, and thus it would be a promising Kitaev material being so far closest to the QSL state.

The emerging magnetic van der Waals (vdW) materials provide a platform for exploring novel physics regarding magnetism in low dimensions and developing ultrathin spintronic applications. Here, we investigate the ultrafast dynamics of excitons in a vdW $\mathrm{NiP}{\mathrm{S}}_3$ crystal. The temporal evolution of the transient reflection spectra indicates that the spin-correlated exciton is formed through photocarrier localization, the rate of which is independent of the magnetic degrees of freedom. However, the recombination rate of these excitons correlates with the long-range magnetic order, likely arising from a spin-flip rooted in the underlying antiferromagnetic background during the recombination. Our findings uncover intertwined coupling between carrier, lattice, and spin degrees of freedom in $\mathrm{NiP}{\mathrm{S}}_3$, which may pave the path toward ultrafast optical manipulation of spin-related quantum states in vdW antiferromagnets.

Topological quantum sensing leverages unique topological features to suppress noise and improve the precision of parameter estimation, emerging as a promising tool in both fundamental research and practical application. In this Letter, we propose a sensing protocol that exploits the dynamics of topological quantum walks incorporating localized defects. Unlike conventional schemes that rely on topological protection to suppress disorder and defects, our protocol harnesses the evolution time as a resource to enable precise estimation of the defect parameter. By utilizing topologically nontrivial properties of the quantum walks, the sensing precision can approach the Heisenberg limit. We further demonstrate the performance and robustness of the protocol through Bayesian estimation. Our results show that this approach maintains high precision over a broad range of parameters and exhibits strong robustness against disorder, offering a practical pathway for topologically enhanced quantum metrology.

Lead zirconate, ${\mathrm{PbZrO}}_3$ (PZO), is a perovskite crystal with an exceptional diversity of possible low-symmetry structures. Its phase transitions that are driven by temperature, field, pressure, and epitaxy are therefore of intense interest from experimental and theoretical viewpoints. Those viewpoints do not yet match in many important aspects. We conduct machine-learning-based molecular dynamics (MD) simulations to investigate several critical properties of PZO and identify recurring experiment–theory inconsistencies that often go underreported. We show that (i) MD correctly reproduces the experimental decoupling of antipolar displacements and octahedral rotations under pressure; (ii) MD predicts a positive electrocaloric effect, in contrast to experimentally observed negative values; and (iii) electric-field-induced transitions in MD proceed from $Pbam$ to $R3c$, whereas experiments suggest a transition to $R3m$. These findings reveal challenging limitations in current MD models—particularly in capturing entropy-driven phase stability—that must be addressed to reconcile simulations with experimental behavior in PZO.

We investigate quasiparticle interference on an altermagnetic Lieb-like lattice and show how a non-spin-polarized scanning tunneling microscopy measurement can yield effectively spin-resolved information. Within a four-site tight-binding model, which can be tuned between an antiferromagnetic and a Lieb-type altermagnetic state, we introduce on-site impurities at distinct sublattice sites and compute the real space local density of states (LDOS) via a Green's function approach. A Fourier transformation of the impurity-induced LDOS yields the characteristic $d$-wave spin-split Fermi surface contours of the altermagnetic phase. Notably, by choosing which sublattice the impurity is placed upon, we show that the scattering amplitudes effectively encode spin-dependent contrasts: Impurities on one of the magnetic sublattices highlights predominantly spin-up contributions along one crystallographic direction, while impurities on the other one favor the complementary spin-down channel and orientation.

Based on the x-ray photoelectron spectra experimental results of tellurides reported in the literature, it is found that in tellurides, in addition to $\mathrm{T}{\mathrm{e}}^{2-}$ ($5s^{2}5p^6$) anions, there are also $\mathrm{T}{\mathrm{e}}^{1-}$ ($5s^{2}5p^5$) anions. The average chemical valences of Te and cations in ${\mathrm{Cr}}_3{\mathrm{Te}}_4$, ${\mathrm{Cr}}_5{\mathrm{Te}}_8$, and ${\mathrm{FeCr}}_2{\mathrm{Te}}_4$ single-crystal materials are then estimated. Using these average chemical valences and an O $2p$ itinerant electron model for magnetic oxides, the magnetic ordering mechanism of these three telluride samples is discussed. At the same time, for these single-crystal magnetic materials subjected to a magnetic field along the easy magnetization direction, the effect of magnetic domain wall movement on the magnetization is taken into account.

Spin memristors are a class of materials that can store memories through the control of spins, potentially leading to novel technologies that address the constraints of standard silicon electronics, thereby facilitating the advancement of more intelligent and energy-efficient computing systems. In this work, we present a spin memristor based on antiferromagnetic materials that exhibit nonlinear Hall memristance. Moreover, the nonlinear Edelstein effect gives rise to memory through the accumulation of magnetic moments associated with the spin of the electrons. We provide a generic symmetry-based analysis that supports the viability of the effect. To achieve a concrete realization of these ideas, we focus on CuMnAs, an antiferromagnetic material which has attracted attention due to its nonlinear response capabilities.

We report the crystal growth, structure, physical properties, and first-principles calculations of a vanadium-based oxytelluride ${\mathrm{Cs}}_{1-\delta }{\mathrm{V}}_2{\mathrm{Te}}_2\mathrm{O}$. The material possesses two-dimensional ${\mathrm{V}}_2\mathrm{O}$ square nets sandwiched by tellurium layers, with local crystallographic symmetry satisfying the spin symmetry for a $d$-wave altermagnet. An antiferromagnetic transition at 293 K is unambiguously evidenced from the measurements of magnetic susceptibility and specific heat. In addition, a secondary transition at $\sim 70\mathrm{K}$ is also observed, possibly associated with a Lifshitz transition. The first-principles calculations indicate robust Néel-type collinear antiferromagnetism in the ${\mathrm{V}}_2\mathrm{O}$ plane. Consequently, spin splittings show up in momentum space, in relation to the real-space mirror/rotation symmetry. Interestingly, the V-$d_{yz}/d_{xz}$ electrons, which primarily contribute to the quasi-one-dimensional Fermi surface, turns out to be fully orbital and spin polarized, akin to the case of a half metal. Our work lays a solid foundation for the potential applications utilizing altermagnetic properties in vanadium-based oxychalcogenides.

${\mathrm{YBaCuFeO}}_5$ and related compounds can sustain chiral magnetic order up to unexpectedly high temperatures. The underlying mechanism, governed by cation disorder, offers a promising route for the development of magnetoelectric spirals operable at ambient temperature. In addition, some chemical substitutions at the A or B sites allow upgrading the spiral stability and reducing significantly the required level of cation disorder in these layered perovskites. In this work, we have addressed the effects of simultaneous divalent substitution at the A and B sites, in Y(Ba,Sr)(Cu,Co)${\mathrm{FeO}}_5$ samples synthesized with the same level of Fe/Cu disorder. This strategy combines the chemical pressure induced by the smaller A-site Sr ions with the reduced uniaxial elongation in the Cu pyramids induced by Co substitution. By enhancing frustration through chemical pressure, we investigated the evolution of the spiral order and its stability relative to other competing magnetic phases. Three distinct regions were identified as a function of Sr content, demonstrating a pronounced interplay between A- and B-site substitutions that substantially alters the phase diagrams obtained for single-site doping. In low-disorder $\mathrm{Y}\left({\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x\right)\left({\mathrm{Cu}}_{0.96}{\mathrm{Co}}_{0.04}\right){\mathrm{FeO}}_5$, ${\mathrm{T}}_{\mathrm{S}1}\approx 300$ K for $x\le 5\%$. At higher Sr concentrations, ${\mathrm{T}}_{\mathrm{S}1}$ decreases and the spiral order eventually disappears abruptly for $x>10\%$.

We study the interference of chiral Majoranas in a magnetic topological insulator thin slab having a grounded section proximity coupled to a superconductor and another section under the influence of top-bottom electrostatic gating. The gated section locally widens an energy gap and mediates the coupling between the quantum anomalous Hall states of the leads and the chiral Majorana states of the proximitized sector. Local and nonlocal conductances offer measurable hints of the existence of transport mediated by chiral Majorana modes. Local conductances on the two leads reveal characteristic oscillatory patterns as a function of the gating strength, with peculiar correlations depending on the distance between gated and proximitized sectors. A gate tunable Majorana diode effect on nonlocal conductances emerges when the chemical potential deviates from zero. We suggest a protocol to identify chiral Majorana physics based on a sequence of electrostatic gates that allows the tuning of chiral Majorana interference.

Quantum criticality has been demonstrated as a useful quantum resource for parameter estimation. This includes second-order, topological, and localization transitions. In all these works reported so far, gap-to-gapless transition at criticality has been identified as a crucial resource for achieving the quantum-enhanced sensing, although there are several important concepts associated with criticality, such as long-range correlation and symmetry breaking. In this work, we show that symmetry-breaking alone can drive a quantum-enhanced sensing, even without any gap-to-gapless transition. We analytically demonstrate that the estimation of the superconducting pairing amplitude in the one-dimensional Kitaev model achieves Heisenberg scaling when the system is prepared near a multicritical point and is varied along a gapless critical line, implying symmetry breaking as a standalone metrological resource. Extending our analysis in the realm of simultaneous multiparameter estimation of both the pairing term and the chemical potential, we show that it is possible to obtain $L^6$ scaling in a narrow parameter range, but with definite observable consequence, where the quantum advantage is assisted by gap-to-gaplees transition as well. Our work thus identifies a new resource for criticality-enhanced quantum sensing, and also suggests multicritical systems as useful platform for multiparameter sensing.

We consider a rhombohedral-stacked $N$-layer graphene coupled to a monolayer of Haldane model. We show that high-order Dirac points in multilayer graphene can be gapped out by the topological proximity effect of the Haldane model layer, leading to total Chern number $\left|C\right|=N+1$ quantum anomalous Hall states. This provides another way to construct high Chern number quantum anomalous Hall states in realistic crystalline graphene systems.

We propose a real-space renormalization group algorithm for accurately coarse-graining two-dimensional tensor networks. The central innovation of our method lies in utilizing variational boundary tensors as a globally optimized environment for the entire system. Based on this optimized environment, we construct renormalization projectors that significantly enhance accuracy. By leveraging the canonical form of tensors, our algorithm maintains the same computational complexity as the original tensor renormalization group (TRG) method, yet achieves higher accuracy than existing approaches that do not incorporate entanglement filtering. Our work offers a practical pathway for extending TRG methods to higher dimensions while keeping computational costs manageable.

Graphene fractal structures are ideal systems to analyze the impact of self-similar geometries on physical properties. Here, we study the electronic transport in graphene Cantor structures. A transmission scheme for the electronic transport is used. In particular, the zero-temperature linear-regime conductance is computed with the Landauer-Büttiker formalism. We obtain the conductance for different generations of the graphene Cantor structure. The fractality of the conductance curves is determined by means of power spectrum analysis, while the fractality of the Cantor-like potential profile is calculated with the box-counting method. The fractality of the conductance curves is strongly related to the fractality of the Cantor-like potential profiles. The power spectrum analysis of the conductance curves also allows us to find the dominant Fermi energies of the electronic transport in graphene Cantor structures. These Fermi energies are related to the embedded periodic structures intrinsic to graphene Cantor structures. To the best of our knowledge, this is the first report using the power spectrum analysis to understand the electronic transport in graphene fractal structures.

Floquet engineering with high-frequency light offers dynamic control over topological phases in quantum materials. While in 3D Dirac systems circularly polarized light is known to induce topological phase transitions via gap opening, linearly polarized light (LPL) has generally been considered ineffective. Here we show that in quasi-2D Dirac materials the second-order momentum term arising from the intersurface coupling can induce a topological phase transition under LPL, leading to chiral edge channels. Considering an ultrathin ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ film as a representative system, we show that this transition occurs at experimentally accessible light intensities. Our results thus promote quasi-2D materials as viable platforms for light-controlled topological phases, expanding the potential of Floquet topological engineering.

${\mathrm{WTe}}_2$ and ${\mathrm{MoTe}}_2$ monolayers offer a rich platform for exploring topological quantum phenomena, including electrically switchable circular photogalvanic effects, rectification, and nonlinear Hall effects (NLHE). In time-reversal symmetric systems, a nonzero Berry curvature dipole (BCD) is essential for realizing NLHE, and such a BCD-induced NLHE has been observed in pristine ${\mathrm{WTe}}_2$ and ${\mathrm{MoTe}}_2$ monolayers. However, the intrinsic BCD in these materials is quite small—on the order of 0.01 Å—posing significant challenges for experimental detection and practical implementation of nonlinear Hall phenomena for technological applications. In this work, we theoretically design a monolayer ${\mathrm{T}}_d\text{−}{\mathrm{W}}_{0.5}{\mathrm{Mo}}_{0.5}{\mathrm{Te}}_2$ (i.e., ${\mathrm{WMoTe}}_4$) by chemically substituting elements in the parent ${\mathrm{WTe}}_2$ and ${\mathrm{MoTe}}_2$ monolayers. Our first-principles calculations confirm the dynamical, elastic, and mechanical stability of the designed monolayer. Remarkably, the ${\mathrm{T}}_d\text{−}{\mathrm{W}}_{0.5}{\mathrm{Mo}}_{0.5}{\mathrm{Te}}_2$ monolayer exhibits a significantly enhanced intrinsic BCD of $\sim$ 4.5 Å (without any strain or external tuning) near the Fermi energy, which is nearly 100× larger than that in pristine {W, Mo}${\mathrm{Te}}_2$ monolayer. This enhancement is attributed to a reduced energy gap, which amplifies Berry curvature contributions near the Fermi energy. Given that bulk ${\mathrm{T}}_d\text{−}{\mathrm{W}}_{0.5}{\mathrm{Mo}}_{0.5}{\mathrm{Te}}_2$ has already been synthesized, the proposed monolayer offers a readily accessible and strain-free 2D platform to harness substantial NLHE for next-generation quantum devices, including high-performance rectifiers and sensors.

Using density functional theory calculations with spin-orbit coupling (SOC), we report on the temperature-dependent thermodynamic properties of Pb: electrical resistivity, thermal expansion (TE), heat capacity, bulk modulus, and its pressure derivative. For the former, we employed the state-of-the-art ab initio Boltzmann transport equation formalism, and we calculated the effect of TE. In accordance with previous work, we show that SOC improves the description of the phonon dispersion and the resistivity. We argue that this is caused by a joint mutual effect of an increase in the electronic nesting and an increase in the electron-phonon coupling. Interestingly, including TE incorporates nonlinearity into the resistivity at high temperatures, whose magnitude depends on whether SOC is included or not. We suggest that mechanisms beyond the quasiharmonic approximation should be considered to get a better description of Pb with SOC at high temperatures.

We develop a gauge-theoretical framework to investigate the quanta of surface plasmons. Our formulation, based on quantum electrodynamics, highlights the importance of residual gauge symmetry. We emphasize that residual gauge symmetry, which imposes constraint equations on physical states, is fundamentally linked to Joule heating. This framework is applied to metals, semiconductors, and quantum Hall states, suggesting the presence of a latent transverse electric mode and that the quanta have the ability to maintain light-matter entanglement.

We develop a microscopic scattering formalism to describe Yu-Shiba-Rusinov (YSR) states due to a single Cr adatom on the Bi-terminated surface of $\beta \text{−}{\mathrm{Bi}}_2\mathrm{Pd}$, by combining ab initio Wannier functions with a real-space Green's function approach in the Bogoliubov–de Gennes formalism. Our framework reproduces key scanning tunneling spectroscopy features, including a single particle-hole asymmetric YSR peak and isotropic $dI/dV$ maps around the impurity. Decomposing the YSR states reveals contributions from four nearly degenerate $C_{4v}$ representations, with energy broadening masking their individual signatures. Spin-orbit coupling induces partial spin polarization, while the spatial asymmetry between particle and hole components arises from Cr $d\text{−}\mathrm{Bi} p$ hybridization. These results highlight the importance of realistic band structures and microscopic modeling for interpreting STM data and provide a foundation for studying impurity chains hosting topological excitations.