The surface optical anisotropy of AlInP(001) surfaces is studied from both experiment and theory. The comparison of the data measured on epitaxially grown ${\mathrm{Al}}_{0.52}{\mathrm{In}}_{0.48}\mathrm{P}\left(001\right)$ epilayers lattice matched to GaAs with spectra calculated for energetically favored AlInP(001) surface structures suggests that the surface is covered with a monolayer of buckled phosphorus dimers, where half of the phosphorus atoms are hydrogen saturated. While the optical anisotropies for photon energies below about 3 eV provide clear fingerprints for the structure of the outermost surface atomic layer, the spectral features at higher energies provide insight into the near surface bulk ordering of AlInP. In particular optical anisotropies at the AlInP critical point energies are found to be related to the CuPt ordering in the material.

Topological insulators hold great promise for dissipationless transport devices due to the robust gapless states inside the insulating bulk gap. So far, several generations of topological insulators have been theoretically predicted and experimentally confirmed, most of them based on three- or two-dimensional materials. Here, on the basis of the first-principles calculations, we predict a quasi-one-dimensional (quasi-1D) topological insulator ${\mathrm{Nb}}_4{\mathrm{SiTe}}_4$ that can be prepared by exfoliation from its three-dimensional bulk phase. This material, characterized by topological ${\mathbb{Z}}_2$ invariants and robust zero-energy edge states, has a large nontrivial gap of $\sim 93.6$ meV, large enough for inhibiting the possibility of the thermal disturbance. Additionally, when applying pressure, we find there is an abnormal force releasing stage originating from the shrinking of the inner Nb atomic rings. In addition, we find that substrate, stacking, defect, and structure deformation have specific effects on electronic properties. Our results reveal a promising quasi-1D topological insulator ${\mathrm{Nb}}_4{\mathrm{SiTe}}_4$ and uncover its unique strain-dependent electronic and mechanical properties.

Recently, near-ambient superconductivity has been experimentally evidenced in a nitrogen-doped lutetium hydride [Nature (London) 615, 244 (2023)], which yields a remarkable maximum $T_c$ of 294 K at just 10 kbar. However, due to the difficulty of x-ray diffraction (XRD) in identifying light elements, such as hydrogen and nitrogen, the crystal structure of the superconductor remains elusive, in particular, for the actual stoichiometry of hydrogen and nitrogen and their atomistic positions. This holds even for its parent structure. Here, we set out to address this issue by performing a thorough density functional theory study on the structural, electronic, dynamical, and optical properties of lutetium hydrides. Through thermal and lattice dynamic analysis as well as XRD and superconductor color comparisons, we unambiguously clarified that the parent structures are a mixture of the dominant ${\mathrm{LuH}}_2$ phase of the ${\mathrm{CaF}}_2$ type (instead of the originally proposed ${\mathrm{LuH}}_3$ structure of the $Fm\overline{3}m$ space group) and the minor LuH phase of the NaCl type.

We numerically study quantum avalanches in one-dimensional disordered spin systems by attaching two XXZ spin chains. One chain has low disorder representing a rare Griffith's region, or thermal inclusion, and the second has larger disorder, i.e., disorder larger than the observed finite-size crossover. Comparing dynamics of this system to identical systems with uniformly large disorder, we find evidence for exponentially slow thermalization (in disorder) within the many-body localized regime when the rare region is present. We observe a decay of the spin imbalance in the bulk of the large disorder region that persists to long times $\left(\sim {10}^4\right)$ and find a universal behavior of the spectral function.

Based on the Bethe ansatz approach and inelastic neutron scattering experiments, we reveal the evolution of confinement of many-body Bethe strings in ordered regions of the quasi-one-dimensional antiferromagnet ${\mathrm{YbAlO}}_3$. In the antiferromagnetic phase, the spin dynamics is dominated by confined length-1 Bethe strings, whose dominancy in the high-energy branch of the excitation spectrum yields to confined length-2 Bethe strings when the material is tuned to the spin-density-wave phase. In the thermal-induced disordered region, the confinement effect disappears, and the system restores the conventional quantum integrable physics of the one-dimensional Heisenberg model. Our results establish a unified picture based on a Bethe string for the spin dynamics in different magnetic phases of ${\mathrm{YbAlO}}_3$, and thus provide profound insight into many-body quantum magnetism.

The performance of superconducting devices is often degraded by the uncontrolled appearance and disappearance of quasiparticles, a process known as poisoning. We demonstrate the electrostatic control of quasiparticle poisoning in the form of single-charge tunneling across a fixed barrier onto a Coulomb island in an InAs/Al hybrid nanowire. High-bandwidth charge sensing was used to monitor the charge occupancy of the island across Coulomb blockade peaks, where tunneling rates were maximal, and Coulomb valleys, where tunneling was absent. Electrostatic gates changed the on-peak tunneling rates by two orders of magnitude for a barrier with fixed normal-state resistance, which we attribute to the gate dependence of the size and softness of the induced superconducting gap on the island, corroborated by separate density-of-states measurements. Temperature and magnetic field dependence of tunneling rates are also investigated.

One-dimensional (1D) chains with nonreciprocal tunneling realizing the non-Hermitian skin effect (NHSE) have attracted considerable interest in the last years, whereas their experimental realization in real space remains limited to a few examples. In this Letter, we propose a generic way of implementing nonreciprocity based on a combination of Rashba-Dresselhauss spin-orbit coupling, existing for electrons, cold atoms, and photons, and a lifetime imbalance between two spin components. We show that one can realize the Hatano-Nelson model, the non-Hermitian Su-Schrieffer-Heeger model, and even observe the NHSE in a 1D potential well without the need for a lattice. We further demonstrate the practical feasibility of this proposal by considering the specific example of a photonic liquid-crystal microcavity. This platform allows one to switch on and off the NHSE by applying an external voltage to the microcavity.

Anderson localization on random regular graphs (RRG) serves as a toy-model of many-body localization (MBL). We explore the transition from ergodicity to localization on RRG with large connectivity $m$. In the analytical part, we focus on the inverse participation ratio of eigenstates and identify several regimes on the ergodic side of the transition—self-consistent golden rule, golden rule, precritical, and critical—that the system consecutively goes through when the disorder increases toward the point $W_c$ of the localization transition. We also perform exact-diagonalization numerics as well as a population-dynamics analysis combining analytical and numerical techniques. Results of all the approaches are in excellent mutual agreement. We further explore the evolution from ergodicity to localization in two models of Fock-space MBL: fermionic and spin quantum dots. Large-connectivity RRG models serve as an approximation for this class of many-body problems; one of our central goals is to better understand the status of this approximation. Our numerical simulations support the conjecture that, in the limit of a large system, there is a sharp ergodicity-to-localization transition in the quantum-dot models. Furthermore, our results are consistent with the RRG-like scaling of the critical disorder, $W_c\sim mlnm$. While in the golden-rule range the behavior of quantum-dot models is in agreement with analytical predictions based on the RRG model, substantial deviations occur in the precritical regime. Our results indicate that the precritical and critical behavior (as well as the numerical coefficient in the formula for $W_c$) in the quantum-dot models may be different from what one would expect from the RRG-like approximation.

We calculate the thermoelectric transport of spin-orbit coupled conduction electrons in the presence of topological spin textures. We show, within a controlled, semiclassical approach that includes all phase space Berry curvatures, that the Nernst effect has two contributions in addition to the usual effect proportional to a magnetic field. These are an anomalous contribution governed by the momentum-space Berry curvature and proportional to net magnetization, and a topological contribution determined by the real-space Berry curvature and proportional to the topological charge density, which is nonzero in skyrmion phases. We derive a generalized Mott relation expressing the thermoelectric tensor as the chemical potential derivative of the conductivity tensor and show how the Sondheimer cancellation in the Nernst effect is evaded in chiral magnets.

Despite the blooming interest, the transition-metal rare-earth ferrimagnets have not been comprehensively understood in terms of their coercivity and transport properties. Here, we report a systematic study of the magnetic and transport properties of ferrimagnetic FeTb alloy by varying the layer thickness and temperature. The FeTb is tuned from the Tb-dominated regime to the Fe-dominated regime via the layer thickness, without varying the composition. The coercivity closely follows the $1/\cos {\theta }_{\mathrm{H}}$ scaling (where ${\theta }_{\mathrm{H}}$ is the polar angle of the external magnetic field) and increases quasiexponentially upon cooling (exceeding 90 kOe at low temperatures), revealing that the nature of the coercivity is the thermally assisted domain-wall depinning field. The resistivity exhibits a quasilinear upturn upon cooling possibly due to thermal vibrations of the structure factor of the amorphous alloy. The existing scaling laws of the anomalous Hall effect in the literature break down for the amorphous FeTb that are either Fe or Tb dominated. These findings should advance the understanding of the transition-metal-rare-earth ferrimagnets and the associated ferrimagnetic phenomena in spintronics.

Three-dimensional magnetic metamaterials feature interesting phenomena that arise from a delicate interplay of material properties, local anisotropy, curvature, and connectivity. A particularly interesting magnetic lattice that combines these aspects is that of nanoscale gyroids, with a highly interconnected chiral network with local three-connectivity reminiscent of three-dimensional artificial spin ices. Here, we use finite-element micromagnetic simulations to elucidate the anisotropic behavior of nanoscale nickel gyroid networks at applied fields and at remanence. We simplify the description of the micromagnetic spin states with a macrospin model to explain the anisotropic global response, to quantify the extent of icelike correlations, and to discuss qualitative features of the anisotropic magnetoresistance in the three-dimensional network. Our results demonstrate the large variability of the magnetic order in extended gyroid networks, which might enable future spintronic functionalities, including neuromorphic computing and nonreciprocal transport.

Since strong quantum fluctuations are essential for the emergence of quantum spin liquids, there have been extensive exploration and identification of spin liquid candidates in spin-$\frac{1}{2}$ systems, while such activities are rare in higher spin systems. Here we report an example of non-Abelian chiral spin liquid emerging in a spin-$\frac{3}{2}$ Heisenberg model on a square lattice. By tuning Heisenberg exchange interaction and scalar chirality interaction, we map out a quantum phase diagram enclosing three conventional magnetic orders and a chiral spin liquid based on density-matrix renormalization group studies. The nature of the spin liquid is identified as a long-sought bosonic version of the Read-Rezayi state that supports non-Abelian Fibonacci anyonic statistics, identified by the ground state entanglement spectrum. Significantly, we establish that the non-Abelian chiral spin liquid emerges through the enlarged local degrees of freedom and enhanced quantum fluctuations near the classical phase boundaries of competing magnetic orders. Our numerical discovery of an exotic quantum spin liquid in a spin-$\frac{3}{2}$ system suggests a route for discovering fractionalized quantum phases in frustrated higher spin magnetic compounds.

We use the density-matrix renormalization group method to investigate the superconductor-insulator transition (SIT) in disordered quasi-one-dimensional systems. Focusing on the case of an interacting spinful Hamiltonian at quarter filling, we contrast the differences arising in the SIT when the parent noninteracting model features flat or dispersive bands. Furthermore, we unveil the critical disorder amplitude that triggers insulating behavior by comparing disorder distributions that preserve or not SU(2) symmetry. While scaling analysis suggests the transition be of a Berezinskii-Kosterlitz-Thouless type for all models (two lattices and two disorder types), only in the flat-band model with Zeeman-like disorder is the critical disorder nonvanishing. In this sense, the flat-band structure does strengthen superconductivity in the presence of attractive interactions. For both flat- and dispersive-band models, (i) in the presence of SU(2)-symmetric random chemical potentials, the disorder-induced transition is from superconductor to insulator of singlet pairs; (ii) for the Zeeman-type disorder, the transition is from superconductor to insulator of unpaired fermions. In all cases, our numerical results suggest no intermediate disorder-driven metallic phase.

The breaking of structural symmetries make two-dimensional Janus materials have additional degrees of freedom that can lead to novel electronic and piezoelectric properties. Although Janus PtSSe and other analogous materials have recently been synthesized or predicted, the discovery of Janus piezoelectrics with large vertical piezoelectricity and a systematic understanding of the piezoelectricity of Pt-based Janus materials are still lacking. Here, we identify two new Janus piezoelectric $\mathrm{Pt}X\text{O}$ ($X=\mathrm{S},\mathrm{Se}$) monolayers with strong out-of-plane piezoelectricity by first-principles calculations. Unlike the symmetric binary systems, $\mathrm{Pt}X\text{O}$ exhibit additional Raman-active modes and their activities can be regularly tuned by the biaxial compressive (tensile) strain, which simultaneously ensures the mechanic, dynamic, and thermal stabilities of $\mathrm{Pt}X\text{O}$. Notably, the out-of-plane $e_{31}\mathrm{s}$ of $\mathrm{Pt}X\text{O}$ are one order larger than those of Janus PtSSe, PtSTe, and PtSeTe. The electronic parts are found to play the dominant role in determining the piezoelectricity of all Pt-based Janus materials, based on which we reveal that the piezoelectric performances of Pt-based Janus materials are generally in proportion to the Bader charge difference and the electronegativity difference ratio of the two asymmetric layers. Moreover, the vertical piezoelectricity can be further enhanced by the compressive strain. Our results indicate that Janus $\mathrm{Pt}X\text{O}$ are candidates for the potential applications on nanoscale piezoelectrics; the discussions about piezoelectricity would help to predict or design other transition metal dichalcogenide based Janus materials with strong out-of-plane piezoelectricity in advance.

We investigate the ground states of spin-$S$ Kitaev ladders using exact analytical solutions (for $S=1/2$), perturbation theory, and the density matrix renormalization group method. We find an even-odd effect: in the case of half-integer $S$, we find phases with spontaneous symmetry breaking (SSB) and symmetry-protected topological (SPT) order; for integer $S$, we find SSB and trivial paramagnetic phases. We also study the transitions between the various phases; notably, for half-integer $S$ we find a transition between two distinct SPT orders, and for integer $S$ we find unnecessary first-order phase transitions within a trivial phase.

Novel two-dimensional electron systems at the interfaces of oxide heterostructures, such as ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$, have attracted much attention as they open a new route to harness the rich quantum phases of transition-metal oxides (TMOs) for potentially useful functionalities not available in conventional semiconductor electronics. For such applications, the controllability of these interface properties is key. For ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$, previous theoretical and experimental investigations of the band offset and the potential profile near the interface have yielded not only quantitatively different but sometimes even contradictory results, e.g., the absence vs presence of a potential gradient in the ${\mathrm{LaAlO}}_3$ film. By analyzing angle-dependent hard x-ray photoelectron spectroscopy (HAXPES) data with a Poisson-Schrödinger model, we determine the charge carrier distribution and the valence band edge profile across the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ interface self-consistently. By systematically controlling the oxygen vacancy concentration, i.e., the doping level, during the photoemission experiments, we derive a comprehensive picture of the band scheme and show that the two-dimensional electron system is always narrowly confined to the interface. We observe a crossover of the band alignment from type II to type I with increasing doping level, which reconciles the striking inconsistencies among the earlier studies. We further find that the strongly nonlinear dielectric response of the ${\mathrm{SrTiO}}_3$ substrates to the electric field is essential for the understanding of the band arrangement at the ${\mathrm{LaAlO}}_3/{\mathrm{SrTiO}}_3$ heterointerface.

Two-dimensional (2D) van der Waals (vdW) magnetic $3d$-transition metal trihalides are a new class of functional materials showing exotic physical properties useful for spintronic and memory storage applications. In this article, we report the synthesis and electromagnetic characterization of single-crystalline vanadium trichloride, ${\mathrm{VCl}}_3$, a novel 2D layered vdW Mott insulator, which has a rhombohedral structure ($\mathrm{R}\overline{3}$, No. 148) at room temperature. ${\mathrm{VCl}}_3$ undergoes a structural phase transition at 103 K and a subsequent antiferromagnetic transition at 21.8 K. Combining core levels and valence bands x-ray photoemission spectroscopy (XPS) with first-principles density functional theory (DFT) calculations, we demonstrate the Mott Hubbard insulating nature of ${\mathrm{VCl}}_3$ and the existence of electron small 2D magnetic polarons localized on V atom sites by V-Cl bond relaxation. The polarons strongly affect the electromagnetic properties of ${\mathrm{VCl}}_3$ promoting the occupation of dispersion-less spin-polarized V-$3d a_{1g}$ states and band inversion with $e_g^{\prime }$ states. Within the polaronic scenario, it is possible to reconcile different experimental evidences on vanadium trihalides, suggesting that also ${\mathrm{VI}}_3$ hosts polarons. Our results highlight the complex physical behavior of this class of crystals determined by charge trapping, lattice distortions, correlation effects, mixed valence states, and magnetic states.

We study the role of the interaction range on the Hilbert-space fragmentation and many-body scar states considering a spin-1/2 many-body Hamiltonian describing a generalized Fredkin spin chain. We show that both scar states and weak fragmentation of the Hilbert space survive for almost any range of the coupling. Moreover, when the interaction range is small enough, there are sectors with definite symmetries such that the ratio between the dimension of their largest fragment and their dimension decays algebraically with the system size. Finally we investigate the effects of such structures of the Hilbert space on the out-of-equilibrium dynamics, triggered by certain initial states, characterized by either local persistent oscillations or nonuniform stationary profile of the magnetization.