Achieving higher-order multistates with significant tunneling electroresistance (TER) and tunneling magnetoresistance (TMR) in van der Waals (vdW) multiferroic tunnel junction at the nanoscale is essential for multifunctional information storage. Based on first-principles calculations, a strategy is proposed using four-layer vdW heterostructures that ferroelectric (FE) bilayer-$\mathrm{G}{\mathrm{a}}_2\mathrm{S}{\mathrm{e}}_3$ sandwiched between two half-metal $\mathrm{CoG}{\mathrm{a}}_2\mathrm{S}{\mathrm{e}}_4$ layers. Reversible transition between quasi-Ohmic and Schottky contacts at the interface can be regulated by FE, stemming from the polarization-field-driven band structure shift and multi-interface electron transfer. Accordingly, the designed symmetric $\mathrm{Cu}/\mathrm{CoG}{\mathrm{a}}_2\mathrm{S}{\mathrm{e}}_4/\mathrm{bilayer}-\mathrm{G}{\mathrm{a}}_2\mathrm{S}{\mathrm{e}}_3/\mathrm{CoG}{\mathrm{a}}_2\mathrm{S}{\mathrm{e}}_4/\mathrm{Cu}$ vdW antiferroelectric multiferroic tunnel junction (AFMFTJ) achieves giant TER and TMR ratios up to $5.43\times {10}^4\%$ and $1.16\times {10}^3\%$, respectively, accompanied by exceptionally low resistance-area product of $0.1\mathrm{\Omega }\mu {\mathrm{m}}^2$. Of note, due to the type-II and degenerate band alignments of bilayer $\mathrm{G}{\mathrm{a}}_2\mathrm{S}{\mathrm{e}}_3$ controlled by FE-polarized directions, the proposed AFMFTJ exhibits bidirectional photoresponse ($R$) up to 23.3 and −23.3 mA/W in FE states, while negligible $R$ in antiferroelectric states. As such, the robust and feeble $R$ are suitable for encoding binary digits as “1” and “0”, respectively, enabling the implementation of photoassisted memory and logic functions. Our findings demonstrate the potential photoelectric spintronic applications of AFMFTJ in nanoscale information storage.

Nonreciprocal charge transport characterized by its intrinsic current-direction dependence holds promising potential for applications in rectification and photodetection. Advances in superconducting materials have further propelled investigations into this phenomenon. In this work, we synthesize single crystals of the noncentrosymmetric superconductor ${\mathrm{ZrTe}}_3$ and fabricate thin nanobelt devices. Systematic investigations reveal a pronounced nonreciprocal signal with a giant nonreciprocal coefficient $\gamma$ reaching $8.5\times {10}^4{\mathrm{T}}^{-1}{\mathrm{A}}^{-1}$. The nonreciprocal response can be effectively modulated through thermal and electrical modulation. As the current and temperature increase, a distinct sign reversal of the nonreciprocal signal even emerges, which may be closely associated with the vortex dynamics within the system. Our findings not only provide new perspectives for understanding the mechanisms of nonreciprocal charge transport but also establish a robust platform for designing energy-efficient rectifying devices.

Relaxation processes following light excitation in semiconductors are key in materials-based quantum technology applications. These processes are broadly studied in atomically thin transition-metal dichalcogenides, quasi-two-dimensional excitonic semiconductors in which atomistic design allows for tunable excited-state properties, such as relaxation lifetimes and photoinduced coherence. In this work, we present a density-matrix-based approach to compute exciton relaxation within a many-body ab initio perspective. We expand our previously developed Lindblad density-matrix formalism to capture multichannel electron-hole pair relaxation processes, including phonon and Coulomb scattering as well as radiative recombination, and we study their effect on the time-resolved excited-state propagation. Using monolayer ${\mathrm{MoSe}}_2$ as a prototypical example, we examine many-body effects on the time-dependent dynamics of photoactive excitations, exploring how the electron-hole pair interactions are reflected in variations of the excitation energy, spectral signature, and state coherence. Our method supplies a detailed understanding of exciton relaxation mechanisms in realistic materials, offering a previously unexplored pathway to study excited-state dynamics in semiconductors from first principles.

We present a theoretical and numerical study of wide-angle photonic flatbands in an all-dielectric metasurface consisting of horizontally aligned dimer resonators. While conventional strategies for realizing bound states in the continuum (BICs) typically rely on suppressing specific Fourier harmonics, we show that robust quasi-BIC flatbands can persist well beyond this restrictive condition. By employing a dimer-based unit cell, the lattice periodicity is effectively doubled, resulting in Brillouin zone folding that maps guided modes from the zone edge to the $\mathrm{\Gamma }$ point, where they couple to free-space radiation. Through multipolar decomposition of the scattered fields, we demonstrate that radiative losses are suppressed via far-field destructive interference between the total electric dipole and magnetic quadrupole moments, leading to high-$Q$ quasi-BICs with remarkable angular tolerance. Analytical modeling confirms that the observed flat dispersion stems not only from tailored Fourier harmonics but also from the intrinsic symmetry and phase coherence of the interfering multipoles. Full-wave simulations validate the emergence of ultraflat photonic bands exhibiting minimal angular dispersion, achieved by controlling the dimer separation. These findings establish a versatile and robust framework wherein Brillouin zone folding provides the momentum-space conditions and multipolar interference ensures angle-insensitive quasi-BIC flatbands, opening avenues for practical applications in slow-light devices, low-threshold nanolasers, and nonlinear photonic platforms.

We report ultralow-temperature ${}^{23}\mathrm{Na}$ NMR measurements on the Ising triangular-lattice antiferromagnet ${\mathrm{Na}}_2\mathrm{BaCo}{\left({\mathrm{PO}}_4\right)}_2$, which precisely resolve the phase diagram under a magnetic field applied along the crystalline $c$ axis. With increasing field, the NMR spectra resolve three ordered phases with distinct spin configurations: the Y, up-up-down (UUD), and V phases. In addition, separated ${\mathrm{V}}_1$ and ${\mathrm{V}}_2$ phases are also identified inside the V phase. The spin-lattice relaxation rate $1/T_1$ demonstrates gapless excitations in both the Y and V phases down to 0.04 K, strongly supporting the spin supersolid nature. However, the phase transitions from the UUD phase to the two supersolid phases exhibit dramatically different behaviors upon cooling. Prior to entering the Y phase, $1/T_1$ identifies a gapless regime within the UUD phase, suggesting a Berezinskii-Kosterlitz-Thouless-like phase above a second-order phase transition. In contrast, the coexistence of the UUD and V phases observed in our experiments provides evidence of a first-order phase transition between them.

The skin effect, where bulk modes collapse into boundary modes, is a key phenomenon in topological non-Hermitian systems, and it has been predominantly studied in spinless systems. Recent studies illustrate the magnetic suppression of the first-order skin effect while ignoring spin. However, the physical significance of a magnetic field in the non-Hermitian skin effect with spin remains elusive. Here, we systematically explore non-Hermitian systems based on generalized Hatano-Nelson models with SU(2) gauge potential fields. We demonstrate that the first-order skin effect can be anomalously induced by a magnetic field through Zeeman coupling in a topologically trivial system without any skin effect at zero field. The direction of such magnetically induced skin modes can be controlled by simply changing the amplitude and polarity of the magnetic field. We also demonstrate a transition between non-Bloch $\mathcal{PT}$ and anti-$\mathcal{PT}$ symmetries in the system, and we uncover the spin-dependent mechanism of non-Bloch $\mathcal{PT}$ symmetry. Moreover, when an external magnetic field is applied, the skin effect exhibits a transition from bidirectional to unidirectional. Our results pave the way for exploring the non-Hermitian skin effect in systems with SU(2) gauge fields, leveraging chirality and nonreciprocity.

Quantum many-body scars (QMBS)—rare eigenstates that evade thermalization—are typically characterized by their low entanglement entropies compared to surrounding thermal eigenstates. However, due to finite-size effects in systems accessible via exact diagonalization, this measure can be ambiguous. To address this limitation, we propose using the correlation matrix spectrum as an alternative probe to identify QMBS. In cases of exact QMBS that either have known analytic expressions or are captured by various frameworks of QMBS, we find that the dimensionality of the null space of the correlation matrix—an integer value, and thus immune to finite-size effects—can qualitatively identify QMBS. Beyond serving as a diagnostic tool, the correlation matrix method enables the manipulation of the QMBS subspace. For approximate QMBS, such as those in the PXP model, we observe that the correlation matrix spectrum features numerous approximate zero eigenvalues, thereby distinguishing these states. We demonstrate the effectiveness and utility of this method with several paradigmatic QMBS examples.

We propose a setup to directly measure the anyonic statistical angle on a single edge of a fr actional quantum Hall system, without requiring independent knowledge of nonuniversal parameters. We consider a Laughlin edge state bent into a closed loop geometry, where tunneling processes are controllably induced between the endpoints of the loop. To illustrate the underlying physical mechanism, we compute the time-dependent current generated by the injection of multiple anyons, and show that its behavior exhibits distinctive features governed by the anyonic statistical angle. The measured current reflects quantum interference effects due to the time-resolved braiding of anyons at the junction. To establish experimental relevance, we introduce a protocol where anyons are probabilistically injected upstream of the loop via a quantum point contact (QPC) source. Unlike in Fabry–Pérot interferometers, where phase jumps occur spontaneously due to stochastic quasiparticle motion, here the phase jumps are deliberately induced by source injections. These events imprint measurable signatures in the cross-correlation noise, enabling a controlled statistical analysis of the braiding phase. We further show that, by varying the magnetic field while remaining within the same fractional quantum Hall plateau, the statistical angle can be extracted without relying on the knowledge of other nonuniversal system parameters. Our results provide a minimal and accessible platform for probing anyonic statistics using a single chiral edge.

Charge ordering induced by strong short-range repulsion in itinerant fermion systems typically follows a two-site alternation pattern. However, the covariance matrix spectrum of the one-dimensional, half-filled, spinless $t-V$ model reveals a post-Hartree-Fock picture at strong repulsion, with emergent four-site disruptions of the underlying staggered mean-field state. These disruptions are captured in a thermodynamically extensive manner by a compact four-fermion coupled cluster (doubles) state (CCS). Remarkably, all properties of this state may be computed analytically by combinatorial means, and also derived from an exactly solvable correlated hopping Hamiltonian. Furthermore, this coupled cluster state can be reexpressed as a low-rank matrix product state (MPS) with bond dimension exactly four. In addition, we unveil a hidden connection between this coupled cluster ansatz and a Rokhsar-Kivelson state (RKS), which is the ground state of a solvable parent quantum tetramer model. The broad picture that we uncover here thus provides deep connections between several core concepts of correlated fermions and quantum chemistry that have previously enjoyed limited synergy. In contrast to a recent perturbative treatment on top of Hartree-Fock theory, our approach asymptotically captures the correct correlations in the $t-V$ model at small $t/V$, and remains a qualitatively accurate approximation even outside the perturbative regime. Our results make the case for further studies of the covariance matrix for correlated electron systems in which ground states have nontrivial unit-cell structure.

Anyonic interferometry is a direct probe of fractional statistics. We propose an interferometry geometry that parallels an optical Mach-Zehnder interferometer and offers several advantages over existing interferometry schemes. In contrast with the currently studied electronic Mach-Zehnder interferometer, our setup has no drain inside the device so that the trapped topological charge is time-independent. In contrast with electronic Fabry-Pérot interferometry, anyons cannot go around the device more than once. Thus, the interference signal has a straightforward interpretation in terms of anyonic statistical phases. The proposed geometry suppresses the undesirable effects of bulk-edge coupling. Moreover, the setup allows for simple exact solutions for the electric current and noise for an arbitrary quasiparticle tunneling strength in a broad range of conditions. The structure of the solutions is similar to that for noninteracting electrons but reflects fractional charge and statistics. We present results for electric current and noise in Jain states and address thermal interferometry at zero voltage bias.

We theoretically study the noncollinear magnetic texture effect on the second-order topological superconductor (SOTSC) phase generated in unconventional $d$-wave superconductors and two-dimensional (2D) quantum spin Hall insulators (QSHI). While the interplay of the $d$-wave superconductor and QSHI has been studied as a platform to realize Majorana corner modes (MCMs), we show that the addition of the spin texture enables the tunability of these MCMs. Each corner of this hybrid system can host one or two Majorana modes depending on the system parameters, in particular, exchange strength and pitch vector of the spin texture. To characterize the higher-order bulk topology, we compute the quadrupolar winding number, which directly corresponds to the number of MCMs acquiring a value of one for four corner modes and two for eight corner modes. We investigate and show the close resemblance in the topological phase diagrams obtained from the low-energy effective Hamiltonian that reveals an emergent in-plane Zeeman field and spin-orbit coupling induced by the spin texture, and the real-space tight-binding lattice model. The microscopic pairing mechanism responsible for the appearance of the SOTSC phase is investigated via an effective bulk pairing analysis, while a low-energy edge theory captures the mechanism behind tunability of MCMs. Our result paves the way for realizing SOTC with multiple MCMs that can be tuned via system parameters.

Stabilizer entropies have been extensively explored in real-space formulations of quantum systems within the framework of resource theory. However, interesting and transparent physics often emerges in momentum space, such as Cooper pairing. Motivated by this, we investigate the momentum space structure of Pauli strings and stabilizer entropies in the one-dimensional transverse field quantum Ising model. By mapping the Ising chain onto momentum space qubits, where the stabilizer state corresponds to the paramagnetic state, we analyze the evolution of the Pauli string distribution for 40 spins. In the ferromagnetic phase, the distribution is broad, whereas in the paramagnetic phase, it develops a two-peak structure. We demonstrate that all ferromagnetic states possess the same degree of nonstabilizerness in the thermodynamic limit, while stabilizer entropies are nonanalytic at the critical point and decrease with increasing transverse field. The momentum space approach to nonstabilizerness not only complements its real-space counterpart but also provides advantages in terms of reducing nonstabilizerness and enhancing classical simulability.

Germanium (Ge) has emerged as a contender for scalable solid-state spin qubits. This interest stems from the numerous attractive properties of hole spin in Ge low-dimensional systems and their compatibility with the standards of silicon processing. Herein we show that the controlled incorporation of Sn into the Ge lattice enables hole spin quantum dots that retain the same advantages as those made of Ge while also providing bandgap directness. The latter is essential for a more efficient interaction with light, a key feature in the implementation of photon-spin interfaces and quantum memories. We first map the band alignment for a range of ${\mathrm{Ge}}_{1-x}{\mathrm{Sn}}_x/\mathrm{Ge}$ quantum wells to identify the optimal conditions to simultaneously achieve hole spin confinement and bandgap directness. We estimate that an additional 4.5 at.% of Sn is needed for every 1% increase in the absolute value of compressive strain to preserve the direct bandgap. Using a Schrieffer-Wolff transformation to evaluate the effective properties of confined heavy-hole states, we show that increased compressive strain leads to a higher light-hole heavy-hole splitting, reducing the Rashba coupling. A theoretical framework is derived to evaluate the dipole moment $d$ and the relaxation rate $\mathrm{\Gamma }$ of electric dipole spin resonance quantum dot devices. We compare the perturbative and effective values of $d$ with the values obtained from the full 3D Hamiltonian. We find $d$ to be around 1 and 0.01 e pm for the out-of-plane and in-plane configurations, respectively, and $\mathrm{\Gamma }\propto B^5$, eventually becoming $\propto B^7$ in the out-of-plane configuration.

We theoretically explore strategies to actively control photon emission from quantum light sources by leveraging the large magneto-optical response of graphene. The quantum electrodynamic response of graphene, characterized by the Purcell factor and the Lamb shift of a proximal emitter, is analyzed for extended two-dimensional sheets, one-dimensional nanoribbons, and zero-dimensional nanodisks, all of which are endowed with an intrinsic chiral near-field response under a static perpendicular magnetic field. Using systematic semianalytical models of these systems, we reveal that the emission properties can be readily tuned by variations in doping charge carrier density and applied magnetic field strength, both with respect to magnetoplasmon resonances (at infrared frequencies) and Shubnikov–de Haas oscillations (entering telecommunication bands) associated with optical transitions between discrete Landau levels. Localized magnetoplasmons in graphene nanoribbons are predicted to induce large dissymmetry in the spontaneous emission from left- and right-hand circularly polarized transitions in a proximal quantum emitter, presenting applications for chiral quantum optical waveguiding. This dissymmetry is further enhanced in gyrotropic graphene nanodisks, signaling that the spatial shaping of near fields in nanostructured graphene can significantly boost the intrinsic chiral response induced by the magnetic field. These results indicate that magneto-optical graphene constitutes a versatile and highly tunable platform for quantum light generation and manipulation at the nanoscale.

Nonreciprocal charge transport (NCT) is defined as a phenomenon where electrical resistance depends on the current direction. It has been drawing much attention because it sensitively reflects the symmetry breaking of material systems. A topological insulator (TI)/superconductor (SC) heterostructure where the topological surface state (TSS) of the TI layer is proximitized with the SC layer is one such system that presents a sizable NCT due to a large spin-orbit coupling and superconductivity. Here, we report a control of the magnitude and sign of NCT: reversal of the direction of NCT by tuning the Fermi energy of TSS of the TI layer with respect to the charge neutral point by systematic regulation of Sb composition $x$ in a TI/SC heterostructure of ${\left({\mathrm{Bi}}_{1-x}{\mathrm{Sb}}_x\right)}_2{\mathrm{Te}}_3/\mathrm{Fe}{\mathrm{Se}}_{0.1}{\mathrm{Te}}_{0.9}$. The result is consistent with the model of a TSS proximitized with superconductivity. Furthermore, we find a significant enhancement of the magnitude of NCT in the TI/SC heterostructures by reducing the thickness of the SC layer. The enhancement can be ascribed to the inversion-symmetry breaking of the $\mathrm{Fe}{\mathrm{Se}}_{0.1}{\mathrm{Te}}_{0.9}$ SC-layer itself adjacent to the TI layer. Our results highlight the essential role of the TSS for exhibiting NCT and offer knobs to control the direction and magnitude of NCT.

${\mathrm{BiFeO}}_3$ is a multiferroic material featuring ferroelectricity and noncollinear antiferromagnetism. Definitive and efficient control of the characteristic spin texture of ${\mathrm{BiFeO}}_3$ is attractive for emerging quantum devices. In this regard, crystal-field $d\to d$ excitations localized on Fe atomic sites in ${\mathrm{BiFeO}}_3$ provide an avenue for manipulation of the spin texture as they induce a complex interplay among the spin, charge, and lattice degrees of freedom. In this work, the ab initio $\mathit{GW}$-BSE method is used to characterize these excitations within an excitonic picture. We find that the $d\text{−}d$ transitions appear as strongly bound, chiral, spin-flip excitons deep within the electronic band gap as a result of the intricate competition between the lattice potential, the antiferromagnetic ordering, the spin-orbit coupling, and the electron-hole interaction. Most crucially, these excitons are composed of electron-hole pairs with opposite spins that constitute almost all of their $\pm \hslash$ total angular momentum. These excitons of specific angular momentum can be selectively excited using circularly polarized light, consequently modulating the local magnetic moment.

Flat bands arising from destructive interference are qualified candidates for hosting exotic states of matter. Here we investigate the spectral and localization features of two interacting particles in a non-Hermitian flat-band lattice, described by a flux-dressed rhombic-Hubbard model with nonreciprocal hoppings, and unravel some intriguing results. In the noninteracting scenario, the flat bands survive under nonreciprocity, and we identify the emergence of two-particle hybridized flat-band states formed by the bonding of a single-particle skin-edge state and a localized flat-band state. Upon strong interactions, we uncover the transition from flat-band localization to skin localization and the emergence of doublon edge states. Remarkably, unlike the interaction-induced flat-band localization in Hermitian cases, we find that the interaction leads to all-dispersive-skin bands for $\pi /2$ flux. A perturbation theory incorporating forth-order processes is developed to understand these results. Finally, we propose a feasible experimental scheme by emulating the two-particle Hilbert space using electric circuits. Our work offers insights into the emergent correlated states in non-Hermitian systems and expands our understanding of non-Hermitian many-body physics.

Nanoscale bilayers containing at least one magnetic layer exhibit universal unusual anisotropic magnetoresistance (UAMR) and unidirectional magnetoresistance (UMR). They are currently understood through various mechanisms related to the interconversion of charge current and spin current, giant magnetoresistance, thermal magnonic effects, thermoelectric effects, and diverse spin-dependent scattering processes. This raises a fundamental question: Do the universal behaviors observed in a wide range of systems stem from underlying general principles? We demonstrate here that both UAMR and UMR arise from electron transport influenced by the magnetization vector present in the magnetic material and the interfacial potential inherent in heterostructures. Specifically, UAMR represents current-independent resistance (resistivity) of bilayers. UMR is the resistance proportional to the current, although electron transports of the bilayers are the linear response to high current densities and their induced thermal gradients. Our theory introduces an approach that considers the interplay between the magnetization vector, thermal gradients, and the effective internal electric field at the interface. This framework provides a unified explanation for both UMR and UAMR, effectively capturing key experimental features such as a dependence on current direction, magnetization orientation, film thickness, and magnetic field strength. Furthermore, it offers a universal perspective that bridges UMR and UAMR effects, enhancing our understanding of spin-dependent transport phenomena in bilayers.

In this study, we systematically compare the impact of a 1.5-nm-thin Ta adhesion layer on the structural and magnetic behavior of Co/Pt multilayers (MLs) sputter-deposited at a low and a high Ar gas pressure. Our focus is a comprehensive structural analysis, centered on real-space cross-sectional scanning transmission electron microscopy (STEM) images, which are then correlated with complementary, reciprocal-space measurements from x-ray reflectometry (XRR) and x-ray diffraction (XRD). Drawing on this comparison and supplemented by atomic force microscopy (AFM), we develop a simplified model to fit the XRR data. Fits and data agree excellently, while the extracted density profiles match well with the STEM data. The structural features are then correlated with the magnetic ones, as determined by magnetic reversal loops and magnetic force microscopy (MFM) images. We find considerably better texture with the adhesion layer, as well as vastly different structural features at the higher deposition pressure between the different underlayers. At the lower pressure, the influence of the underlayer is much less pronounced. Magnetically, the Ta layer results in a marked improvement in the effective perpendicular magnetic anisotropy (PMA), increasing it up to an impressive 340% at the higher pressure, while remaining comparable at the lower one. We attribute the changes in structure and magnetism to two different factors: (1) The adhesion layer stops the implantation of Pt atoms into the substrate, improving layer smoothness and texture. (2) The momentum transfer to the film is reduced at higher sputter pressures, which reduces intermixing between Co and Pt, but increases overall roughness. Combining both, the roughness remains small enough to enable well-defined grains with sharper Co/Pt interfaces and lower intragrain curvature, resulting in the increased PMA. Our study provides a practical approach for controlling anisotropy in sputter-deposited ML systems containing heavy atom species, utilizing different combinations of adhesion layer and sputter pressure.