The obstructed atomic insulators are insulators with both atomic limits and boundary states. In this study, we examine the properties of obstructed atomic insulators under correlation. We utilize symmetry indicators by constructing many-body wave functions in momentum space. Our findings show that the obstruction properties, evidenced by boundary modes, persist even at high correlation levels (large $U$) where the charge freedom is strongly gapped. This suggests that the obstructed atomic insulator phase can seamlessly transition to its Mott phase without undergoing a Mott transition. Our analysis encompasses a variety of models, including the Su-Schrieffer-Heeger chain, an anisotropic square lattice model, and the quadrupole insulator model.

The condensed-matter realization of chiral anomaly has attracted tremendous interest in exploring unexpected phenomena of quantum field theory. Here, we show that one-dimensional (1D) chiral anomaly (i.e., 1D nonconservational chiral current under a background electromagnetic field) can be realized in a generalized Su-Schrieffer-Heeger model where a single gapless Dirac cone occurs. Based on the topological Thouless pump and anomalous dynamics of chiral displacement, we elucidate that such a system possesses the half-integer quantization of the winding number. Moreover, we investigate the evolution of 1D chiral anomaly with respect to two typical types of disorder, i.e., on-site disorder and bond disorder. The results show that the on-site disorder tends to smear the gapless Dirac cone. However, we propose a strategy to stabilize the half-integer quantization, facilitating its experimental detection. Furthermore, we demonstrate that the bond disorder causes a unique crossover with disorder-enhanced topological charge pumping, driving the system into a topological Anderson insulator phase.

The screening response of valence and core electrons against a test charge embedded in a metal is investigated. The real space-and-time dynamical response function $\chi (r,t)$ is derived from the x-ray inelastic scattering spectra measured over a wide momentum and energy space on elementary Li. Embedding a charge initially induces local screening due to core electrons. This is followed by screening due to valence electrons, which exhibits an oscillatory behavior where the frequency is determined by the plasmon energy. Finally, static screening charges are produced. The static screening charge consists of a local electron cloud surrounding the embedded charge over several angstroms and the oscillatory charge densities have a periodicity twice that of the Fermi wave number in a larger $r$ scale (i.e., the Friedel oscillation). The core electrons also exhibit an oscillatory behavior, where the frequency is determined by the absorption edge energy. This eventually leads to more local screening, further reducing the screening distance.

We present a quantum transport theory for hybrid superconducting systems based on our exact master-equation approach. The system-terminal transport current dynamics are fully captured by the extended nonequilibrium Green's function incorporating pair correlations via spectral density matrices. The total transient transport current is decomposed into components that describe coherent transports through different paths of particle and hole channels. We show that these coherent transports are resultant interferences of numerous repeated tunneling processes and cannot be rendered as a simple normal transmission or Andreev reflection as usually described in the steady quantum transport involving superconductivity. As a practical application, we apply the theory to a two-terminal superconductor-semiconductor nanowire to study the transport dynamics through a pair of Majorana zero modes. We find that the coherent transport currents passing through a pair of well-separated Majorana zero modes vanish due to the totally destructive interference between the particle and hole channels. This provides a different understanding to the scenario of “teleportation” via a pair of delocalized Majorana zero modes, namely, a pair of delocalized Majorana zero modes does not possess the nonlocality of an entangled pair for quantum teleportation.

The magnetic exchange interaction of ${\mathrm{Fe}}_n$ $(n=1,2,3)$ clusters with the quasiparticles of superconducting Pb(111) is probed by scanning tunneling spectroscopy of Yu-Shiba-Rusinov states. The spectral weight of the Yu-Shiba-Rusinov resonances is shifted from the coherence peaks in the Fe monomer spectrum towards the Fermi energy in the Fe dimer spectrum. Unexpectedly, the linear Fe trimer does not follow this trend, as it exhibits an almost identical spectrum to the single Fe atom. Kinked Fe trimers where one of the end atoms deviates from the linear orientation, in contrast, show strong Yu-Shiba-Rusinov resonances well within the Bardeen-Cooper-Schrieffer energy gap of the substrate. First-principles simulations of the Yu-Shiba-Rusinov states reveal which adsorption geometries and magnetic structures of the clusters can reproduce the experimental spectra most accurately.

Modes with a high-$Q$ factor are crucial for photonic metadevices with advanced functionalities. In sharp contrast to recent techniques which generate a supercavity mode by bound states in the continuum via symmetry breaking, we reveal a general and different route, by stacking two parallel and identical Mie-resonant metasurfaces with an air separation. The supercavity mode can be designed by the established theoretical model by overlapping Mie resonant modes with tailor-made Fabry-Pérot modes. The simplified system, with free-space field concentration which can exist in plane as well as out of plane of the metasurfaces, provides for ease of integration with added matter, creating exciting opportunities for the study of fundamental light-matter coupling. This work deepens our understanding of light manipulation using metasurfaces. It paves a different and general route for generating supercavity modes which can be easily engineered and controlled for different applications of all dielectric metaoptics.

${\mathrm{BaNi}}_2{\mathrm{As}}_2$, a nonmagnetic superconductor counterpart to ${\mathrm{BaFe}}_2{\mathrm{As}}_2$, has been shown to develop nematic order, multiple charge orders, and a dramatic sixfold enhancement of superconductivity via isovalent chemical substitution of Sr for Ba. Here we present high-pressure single-crystal and powder x-ray diffraction measurements of ${\mathrm{BaNi}}_2{\mathrm{As}}_2$ to study the effects of tuning lattice density on the evolution of charge order in this system. Single-crystal x-ray experiments track the evolution of the incommensurate ($Q=0.28$) and commensurate ($Q=0.33$ and $Q=0.5$) charge orders, and the tetragonal-triclinic distortion as a function of temperature up to pressures of 10.4 GPa, and powder-diffraction experiments at 300 K provide lattice parameters up to 17 GPa. We find that applying pressure to ${\mathrm{BaNi}}_2{\mathrm{As}}_2$ produces a similar evolution of structural and charge-ordered phases as found as a function of chemical pressure in ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Ni}}_2{\mathrm{As}}_2$, with coexisting commensurate charge orders appearing on increasing pressure. These phases also exhibit a similar abrupt cutoff at a critical pressure of ($9\pm 0.5$) GPa, where powder-diffraction experiments indicate a collapse of the tetragonal structure at higher temperatures. We discuss the relationship between this collapsed tetragonal phase and the discontinuous phase boundary observed at the optimal substitution value for superconductivity in ${\mathrm{Ba}}_{1-x}{\mathrm{Sr}}_x{\mathrm{Ni}}_2{\mathrm{As}}_2$.

We demonstrate that a complete class of flat-band lattices with underlying commutative local symmetries exhibit a locally fragmented Hilbert space. The equitable partition theorem ensures distinct parities for the compact localized states (CLSs) present in this class of flat-band lattices and the extended eigenstates of the system. In the presence of on-site bosonic interactions, such models exhibit a conserved quantity, the parity of the number of particles located in all the CLSs in a unit cell. As a consequence, the Hilbert space presents local fragmentation, which is only revealed upon rotating the basis of the Hamiltonian that decouples the CLSs at the single-particle level. We find that the fragmentation is strong and also robust to the addition of long-range interactions. As an example, we numerically analyze the fragmentation of the one-dimensional pyrochlore chain, which exhibits nonintegrable sectors, effective single-particle sectors, and frozen states. We also show that the entanglement entropies form a nested-dome structure typical of these fragmented systems and that thermalization is restricted to each subsector.

Coexistence of localized and extended excitations is central to the macroscopic properties of correlated materials. For $5d$ transition-metal compounds, electron correlations alone generally do not lead to a metal-insulator (Mott) transition, with insulating behavior usually resulting from their coupling with magnetic ordering and/or structural distortions. $1T-\mathrm{Ta}{\mathrm{S}}_2$ is a prototypical example of such correlated insulating behavior, with a high-symmetry metallic phase transforming into a distorted, charge-density wave (CDW) insulating state at low temperatures. The nature of the insulating phase as well as the existence and relevance of the localized electron physics remains debated. We resolve this standing controversy in $1T-\mathrm{Ta}{\mathrm{S}}_2$ combining resonant inelastic x-ray spectroscopy and first-principles calculations. We observe five electronic excitations arising from the interband transitions of the Ta $5d$ orbitals and the S $3p$ ligand state, with none of the excitations on the order of the Mott gap. These excitations cannot be explained within the framework of standard multiplet calculations that assume a localized wave function, but instead, are captured by a band-theory framework accounting for the low symmetry of the crystal field in the CDW state. Our findings suggest that the electronic properties of $1T-\mathrm{Ta}{\mathrm{S}}_2$ are dominated in the visible by both plasmonic quasiparticles and interband transitions, with no resonance associated with a putative Mott transition observed in the 0–3 eV energy range. Our discovery provides insights into the electron localization and the Mott vs band-insulator debate in $1T-\mathrm{Ta}{\mathrm{S}}_2$ and other transition-metal materials.

We have used a polarized spatially resolved microluminescence technique to investigate photocarrier charge and spin transport at 6 K in a GaAs nanowire (NW; n-type doping level $\approx {10}^{17}{\mathrm{cm}}^{-3}$). Because of the difference in expansion coefficients of the NW and of its ${\mathrm{SiO}}_2$ substrate, the NW is under strain, as revealed by the splitting between light- and heavy-hole emissions in the luminescence intensity spectrum. Light valence levels lie above the heavy valence ones, which is attributed as being caused by a tensile strain along both the axial and the lateral directions of the NW, equivalent to a compressive strain in the direction of light excitation. The symmetry group of the perturbed nanowire is then lowered to $C_{2v}$. No spin polarization can be evidenced for the heavy valence levels. The electron spin polarization decays up to a distance of $5\mu \mathrm{m}$ from the excitation spot, because of spin relaxation, and stays constant for larger distances because of the increased value of the drift velocity. Remarkably, the light-hole spin polarization exhibits damped spatial oscillations over as much as $5\mu \mathrm{m}$. Analysis of the effect of strain on valence states shows that these oscillations are caused by the spin-orbit interaction in the light valence level. It is found that, for the $C_{2v}$ point group, the corresponding Hamiltonian is linear in momentum. This spin-orbit interaction causes coherent oscillations rather than a spin relaxation process since transport essentially has a drift character in the internal electric field. The equivalent effective magnetic field induced by spin-orbit interaction and strain is, taking a light-hole $g$ factor of 1, of the order of $60\mathrm{mT}$.

Vicinal surfaces of bismuth are unique test beds for investigating one-dimensional (1D) spin-polarized surface states that may one day be used in spintronic devices. In this paper, such states have been observed for the (112) surface when measured using angle- and spin-resolved photoemission spectroscopy, and also when calculated using a tight-binding model and with density functional theory. The surface states appear as elongated Dirac-cones which are 1D and almost dispersionless in the ${\mathbf{k}}_{\text{y}}$ direction, but disperse with energy in the orthogonal ${\mathbf{k}}_{\text{x}}$ direction to form two $\times$-like features centered at the ${\mathbf{k}}_{\text{y}}$ line through $\overline{\mathrm{\Gamma }}$. Unlike many materials considered for spintronic applications, their 1D nature suggests that conductivity and spin-transport properties are highly dependent on direction. The spin polarization of the surface states is mainly in plane and parallel to the 1D states, but there are signs of a tilted out-of-plane spin-vector component for one of the features. The Bi(112) surface states resemble those found for other vicinal surfaces of bismuth, strongly indicating that their existence and general properties are robust properties of vicinal bismuth surfaces. Furthermore, differences in the details of the states, particularly related to their spin polarization, suggest that the electronic band structure may be engineered simply by precise cutting and polishing of the crystal.

Subharmonics of electric dipole spin resonance (EDSR) mediated by Landau-Zener-Stückelberg-Majorana tunneling transitions are studied numerically and analytically in a Zeeman-split four-level system with strong spin-orbit coupling that can be realized, for example, in a GaAs-based double quantum dot in a single-hole regime. The spin qubit is formed in one of the dots and the second dot is used as an auxiliary element to enhance functionality of the spin qubit. In particular, it is found that the spin rotation rate can be essentially enhanced due to the tunnel coupling with the auxiliary dot on both the main EDSR frequency and at its high subharmonics allowing the coherent spin $\pi$ rotations on a 10-ns timescale. Spin manipulation on high subharmonics is promising for new time-efficient schemes of the spin control and readout in qubit devices operating at high magnetic fields where the main harmonic is inaccessible due to hardware limitations.

Quantum batteries are quantum systems that potentially serve as fuel for other quantum devices by receiving and supplying energy. In this Letter, we investigate the charging processes of a state-of-the-art quantum battery made of a harmonic oscillator, which can store infinite amounts of energy in principle. We experimentally simulate the charging process using a high-dimensional photonic quantum system with multiple concatenated interferometers. Our experiments demonstrate that both the stored and extractable energy of the quantum battery can be significantly improved by introducing a catalyst system. This charging protocol has the same performance as optimized the frequency of the external field in the direct charging protocol but is more convenient without the requirement of probing the global frequency of the charge-battery system. From the viewpoint of experimental innovation, we propose a general method to deterministically implement an arbitrary trace-preserving nonunitary channel and realize it experimentally. Our work shows the potential of this interesting quantum battery and sheds light on experimental investigations of quantum batteries.

We report two nondegenerate magnon modes with opposite spins or chiralities in collinearly antiferromagnetic insulators driven by symmetry-governed anisotropic exchange couplings. The consequent giant spin splitting contributes to spin Seebeck and spin Nernst effects generating longitudinal and transverse spin currents when the temperature gradient applies along and away from the main crystal axis, without requiring any external magnetic field and spin-orbit coupling. Based on first-principle calculations, we predict feasible material candidates holding robust altermagnetic spin configurations to efficiently transport spin. The spin Seebeck conductivity is comparable to the records of antiferromagnets that require the magnetic field, and the spin Nernst conductivity is two orders in magnitude larger than that in antiferromagnetic monolayers that need Berry curvature.

Spin-dependent electron tunneling through a voltage-biased microconstriction between two bulk superconductors is shown to create a dc component of the magnetization in the superconductors near the constriction and an ac Josephson-like spin current. The static magnetization appears in one superconductor even if the other is replaced by a normal conductor. Although spin-dependent tunneling generates quantum spin fluctuations also in the absence of a bias, the formation of spin-triplet Cooper pairs, necessary for the creation of magnetization, is blocked by destructive interference between different quasielectron and quasihole tunneling channels, unless there is an asymmetry between the tunneling densities of states for electrons and holes. Breaking the symmetry in the electron-hole tunnel density of states and creating electron-hole tunneling imbalance by biasing the device destroys the destructive interference and enables triplet Cooper-pair formation. As a result, magnetizing the superconductor becomes possible. The role of the voltage in lifting the blockade hindering the spin-triplet Cooper pair formation is an example of an electrically controlled dissipationless spintronic phenomenon.

We model the isotropic depinning transition of a domain wall using a two-dimensional Ginzburg-Landau scalar field instead of a directed elastic string in a random media. An exact algorithm accurately targets both the critical depinning field and the critical configuration for each sample. For random bond disorder of weak strength $\mathrm{\Delta }$, the critical field scales as ${\mathrm{\Delta }}^{4/3}$ in agreement with the predictions for the quenched Edwards-Wilkinson elastic model. However, critical configurations display overhangs beyond a characteristic length $l_{\mathtt{0}}\sim {\mathrm{\Delta }}^{-\alpha }$, with $\alpha \approx 2.2$, indicating a finite-size crossover. At large scales, overhangs recover the orientational symmetry which is broken by directed elastic interfaces. We obtain quenched Edwards-Wilkinson exponents below $l_{\mathtt{0}}$ and invasion percolation depinning exponents above $l_{\mathtt{0}}$. A full picture of domain-wall isotropic depinning in two dimensions is hence proposed.

We study surface states in the three-dimensional topological insulators ${\mathrm{Bi}}_2{\mathrm{Te}}_{3-x}{\mathrm{Se}}_x$ ($x=0,2,3$) by polarization resolved resonant Raman spectroscopy. By tracking the spectral intensity of the surface phonon modes with respect to the incident photon energy, we show that the surface phonons are qualitatively similar to their bulk counterparts. Using the resonant Raman excitation profile, we estimated the energy gaps between the surface conduction bands and the bulk conduction bands. In addition, we selectively excite the surface-to-bulk electronic continuum near the Fermi energy in ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ to determine the strength of Fano interaction between the most prominent surface phonon and the surface-to-bulk continuum.

In this work we present a comprehensive study of the spin dynamics and fluctuations in the ordered magnetic phases of the prototype multiferroic material $\mathrm{TbMn}{\mathrm{O}}_3$. From the temperature dependence of the dynamical and static components of the time-dependent asymmetry, we demonstrate the existence of strong local magnetic-field disorder arising from the modulated ${\mathrm{Mn}}^{3+}$ spin arrangement and the effect of the ${\mathrm{Tb}}^{3+}$ ordering at low temperatures. We provide evidence for an unusual magnetostructural coupling in the paramagnetic phase of $\mathrm{TbMn}{\mathrm{O}}_3$ by means of muon spin spectroscopy. No short-range magnetic ordering definitively occurs in the paramagnetic phase and the unusual properties found in the temperature dependence of the magnetic susceptibility are due to a magnetostructural coupling, likely involving oxygen displacements.

The key to the next-generation spintronic devices is to design above-room-temperature two-dimensional antiferromagnets with large magnetic moments and anisotropy energies. We propose a design strategy to maximize the utilization of $d$ electrons and the strong coupling of transition-metal atoms. The designed semiconducting ${\mathrm{Cr}}_2\mathrm{BN}$ monolayer consists of hexagonal ${\mathrm{Cr}}_6\mathrm{BN}$ tiles centered by BN dimers. Compared to isolated B or N atoms, the BN dimer in ${\mathrm{Cr}}_2\mathrm{BN}$ can reduce the charges donated by Cr atoms, whereas the short Cr-Cr distance favors strong direct-exchange coupling interaction. These features make the ${\mathrm{Cr}}_2\mathrm{BN}$ monolayer checkerboard antiferromagnetic with a high Néel temperature of 874 K, a large magnetic anisotropy energy of 103 µeV/Cr, and a large magnetic moment of $3.79{\mu }_{\mathrm{B}}$. High structural stability, originating from the covalent BN dimer and Cr-B/N ionic bond, renders ${\mathrm{Cr}}_2\mathrm{BN}$ a good candidate for experimental synthesis.

Understanding the dynamics of magnetic vortices has emerged as an important challenge regarding the recent development of spin-torque vortex oscillators. Either micromagnetic simulations or the analytical Thiele equation approach are typically used to study such systems theoretically. This work focuses on the precise description of the restoring forces exerted on the vortex when it is displaced from equilibrium. In particular, the stiffness parameters related to a modification of the magnetic potential energy terms are investigated. A method is proposed to extract exchange, magnetostatic, and Zeeman stiffness expressions from micromagnetic simulations. These expressions are then compared to state-of-the-art analytical derivations. Furthermore, it is shown that the stiffness parameters depend not only on the vortex core position, but also on the injected current density. This phenomenon is not predicted by commonly used analytical Ansätze. We show that these findings result from a deformation of the theoretical magnetic texture caused by the current-induced Ampère-Oersted field.