We measured the magneto-reflectivity spectra (4–90 meV, 0–16 T) of the triple-point semimetal GdPtBi and found them to demonstrate two unusual broad features emerging in field. The electronic bands of GdPtBi are expected to experience large exchange-mediated shifts, which lends itself to a description via effective Zeeman splittings with a large $g$ factor. Based on this approach, along with an ab initio band structure analysis, we propose a model Hamiltonian that describes our observations well and allows us to estimate the effective $g$ factor, $g^{*}=95$. We conclude that we directly observe the exchange-induced ${\mathrm{\Gamma }}_8$ band inversion in GdPtBi by means of infrared spectroscopy.

We identify several distinct phases of thermalization that describe regimes of behavior in isolated, periodically driven (Floquet), mesoscopic quantum chaotic systems. In doing so, we also identify a Floquet thermal ensemble, the “ladder ensemble,” that is qualitatively distinct from the “featureless infinite-temperature” state that has long been assumed to be the appropriate maximum-entropy equilibrium ensemble for driven systems. The phases we find can be coarsely classified by (i) whether or not the system irreversibly exchanges energy of order $\omega$ with the drive, i.e., Floquet thermalizes, and (ii) the Floquet thermal ensemble describing the final equilibrium in systems that do Floquet thermalize. These phases are representative of regimes of behavior in mesoscopic systems, but they are sharply defined in a particular large-system limit where the drive frequency $\omega$ scales up with system size $N$ as the $N\to \infty$ limit is taken: we examine frequency scalings ranging from a weakly $N$-dependent $\omega \left(N\right)\sim logN$, to stronger scalings ranging from $\omega \left(N\right)\sim \sqrt{N}$ to $\omega \left(N\right)\sim N$. We show that the transition where Floquet thermalization breaks down happens at an extensive drive frequency and, beyond that, systems that do not Floquet thermalize are distinguished based on the presence or absence of rare resonances across Floquet zones. We produce a thermalization phase diagram that is relevant for numerical studies of Floquet systems and experimental studies on small-scale quantum simulators, both of which lack a clean separation of scales between $N$ and $\omega$. A striking prediction of our work is that, under the assumption of perfect isolation, certain realistic quench protocols from simple pure initial states can show Floquet thermalization to a type of Schrodinger-cat state that is a global superposition of states at distinct temperatures. Our work extends and organizes the theory of Floquet thermalization, heating, and equilibrium into the setting of mesoscopic quantum systems.

We have investigated the dynamical magnetic properties of the V-based kagome stibnite compounds by combining the ab initio-extracted magnetic parameters of a spin-Hamiltonian, like inter-site exchange parameters, magnetocrystalline anisotropy and site projected magnetic moments, with full-fledged simulations of atomistic spin- dynamics. Our calculations reveal that, in addition to a ferromagnetic order along the [001] direction, the system hosts a complex landscape of magnetic configurations comprised of commensurate and incommensurate spin spirals along the [010] direction. The presence of such chiral magnetic textures may be the key toward solving the mystery about the origin of the experimentally observed inherent breaking of the $C_6$ rotational, mirror, and the time-reversal symmetry.

We discuss theoretically a ferromagnetic monolayer with an interfacial Dzyaloshinskii-Moriya interaction (iDMI) and a small axial anisotropy. It is shown that the system has a long-period cycloid magnetic order slightly distorted by the anisotropy whose modulation vector $\mathbf{k}$ can have several orientations. We find that due to iDMI-induced umklapp terms in the Hamiltonian, the spectrum of long-wavelength magnons is essentially anisotropic: it is linear and quadratic for momenta directed along and perpendicular to $\mathbf{k}$, respectively. Due to such a quasi-1D spectrum, the temperature correction to the mean spin value has a power-law singularity hampering the magnetic ordering at $T\ne 0$. We demonstrate that the umklapps lead to a peculiar band structure of the magnon spectrum similar to electronic bands in solids. We discuss also the effect of vacancies and defect bonds on system properties at $T=0$. Owing to the quasi-1D character of the spectrum, the distortion of the cycloid structure by a single defect bond is described at long distances by the field of a 1D electric dipole. As a result, even infinitesimal concentrations of defects $c$ destroy the long-range order and establish a short-range order whose correlation length shows a power-law dependence on $1/c$. Our findings should also be applicable to ultrathin films with strong enough iDMI.

Although ${\mathrm{SrNi}}_2{\mathrm{P}}_2$ adopts the common ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ structure for $T\ge 325$ K, being in an uncollapsed tetragonal state rather than a collapsed tetragonal version, it is a special case for the ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ class: on cooling below 325 K it adopts a one-third collapsed orthorhombic phase where one out of every three P rows bonds across the Sr layers. On the other hand, ${\mathrm{SrCo}}_2{\mathrm{P}}_2$ only exhibits the uncollapsed ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ structure from room temperature down to 1.8 K. Regardless of their low-temperature structures, neither ${\mathrm{SrNi}}_2{\mathrm{P}}_2$ nor ${\mathrm{SrCo}}_2{\mathrm{P}}_2$ manifests magnetic transitions down to 50 mK and 2 K, respectively. In this work we report the effects of Co substitution in $\mathrm{Sr}{\left({\mathrm{Ni}}_{1-x}{\mathrm{Co}}_x\right)}_2{\mathrm{P}}_2$, which allows for tuning the transition between the one-third collapsed and the uncollapsed structure. We find a rapid decrease of the one-third collapsed structural transition temperature with increasing Co fraction, until reaching full suppression for $x\ge 0.1$. Substitution levels in the range $0.11\le x\le 0.58$ show no signs of any transition down to 1.8 K in the magnetization or resistance measurements in the range $1.8\le T\le 300\text{K}$. However, different magnetically ordered states emerge for $x\ge 0.65$, and disappear for $x\ge 0.99$, recovering the known paramagnetic properties of the parent compound ${\mathrm{SrCo}}_2{\mathrm{P}}_2$. These results are summarized in a phase diagram, built upon the characterization by energy dispersive x-ray spectroscopy, x-ray diffraction, temperature-dependent resistance, and field- and temperature-dependent magnetization measurements done on single crystals with different Co fraction. Both the magnetic and structural properties are compared to other systems with ${\mathrm{ThCr}}_2{\mathrm{Si}}_2$ structure that exhibit magnetic ordering and collapsed tetragonal transitions. The magnetic ordering and moment formation are well described by Takahashi's spin fluctuation theory of itinerant electron magnetism [Y. Takahashi, J. Phys. Soc. Jpn. 55, 3553 (1986)].

We utilize statistical tools to analyze the magnetic domain wall dynamics in a nanostrip, which can quantify the magnitude and reveal the effects of interfacial Dzyaloshinskii-Moriya interaction (DMI). We find that two peaks in the velocity frequency spectrum exist, the magnitude ratio of which can be used to determine the DMI strength. Our approach is validated by the collective-coordinate model and is demonstrated to be robust against thermal noise and material impurities. Moreover, the third-order cumulant and third-order time-dependent correlation function of velocity are calculated and yield valuable information regarding the asymmetry induced by DMI. Our findings offer efficient analysis tools to understand the physical process of domain wall dynamics under DMI and exotic magnetic phenomena.

We present an algorithm for computing melting points by autonomously learning from coexistence simulations in the NPT ensemble. Given the interatomic interaction model, the method makes decisions regarding the number of atoms and temperature at which to conduct simulations, and based on the collected data predicts the melting point along with the uncertainty, which can be systematically improved with more data. We demonstrate how incorporating physical models of the solid-liquid coexistence evolution enhances the algorithm's accuracy and enables optimal decision making to effectively reduce predictive uncertainty. To validate our approach, we compare the results of 20 melting point calculations from the literature to the results of our calculations, all conducted with the same interatomic potentials. Remarkably, we observe significant deviations in about one-third of the cases, underscoring the need for accurate and reliable algorithms for materials property calculations.

Dynamic magnetic textures may transfer the angular moment from the varying-in-time antiferromagnetic order to spins of conduction electrons. Due to the spin-orbit coupling, these spin excitations can induce the electric current of conduction electrons. We calculated the electric current and the electromotive force, which are produced by a domain wall (DW) moving parallel to the magnetically compensated interface between an antiferromagnetic insulator (AFMI) and a two-dimensional spin-orbit-coupled metal. Spins of conduction electrons interact with localized spins of a collinear AFMI through the interface exchange interaction. The Keldysh formalism of nonequilibrium Green's functions was applied for the analysis of this system. It is shown that a Bloch DW generates the current perpendicular to the DW motion direction. At the same time, a Néel DW creates the electric potential which builds up across the wall. The total charge which is pumped by a Bloch DW can be expressed in terms of a topologically invariant charge quantum. The latter does not depend on variations of the DW's velocity and shape. These effects increase dramatically when the Fermi energy approaches the van Hove singularity of the Fermi surface. The obtained results are important for the electrical detection and control of dynamic magnetic textures in antiferromagnets.

We propose a two-fluid description of fractional quantum Hall systems, in which one component is a condensate of composite bosons and the other is a Fermi liquid formed by composite fermions (or simply electrons). We employ the theory to model the interface between a fractional quantum Hall liquid and a (composite) Fermi liquid metal, where we find a penetration of quantum Hall condensate into the metallic region reminiscent of the proximity effect in superconductor-metal interfaces. We also find a physically reasonable set of gapped quasielectron and neutral modes in fractional quantum Hall liquids.

The recent experimental observations of loop current in ${\mathrm{Sr}}_2{\mathrm{IrO}}_4,$ ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_7,$ and ${\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ have inspired a theoretical study that broadly redefines loop current as a manifestation of quantum liquid crystals. Using the density-matrix renormalization group method, we investigate the emergence of spin loop-current (sLC) textures in carrier-doped (i) excitonic insulators, (ii) orbital-selective Mott insulators, and (iii) two-dimensional Mott insulators, modeled by a two-orbital Hubbard model on a ladder lattice in (i) and (ii) and a single-orbital Hubbard model on a square lattice in (iii). Calculating the spatial distribution of spin current around a bond to which a pinning field is applied, we find conditions for longer-ranged sLC correlations. In system (i), when using the model parameters employed to describe the excitonic condensation, we find that a sLC texture appears near half-filling, associated with an excitonic condensation in a spin channel. In system (ii), using typical sets of model parameters for ${\mathrm{BaFe}}_2{\mathrm{Se}}_3$, we find that a sLC texture appears at electron fillings where a block-type antiferromagnetism develops. In system (iii), introducing a next-nearest-neighbor hopping $t^{\prime }\sim -0.25$ (in units of the nearest-neighbor hopping) suggested for high-$T_{\text{c}}$ cuprates, we find that an axial-sLC texture emerges at hole-carrier density $\delta =0.125$, where the charge stripe simultaneously appears.

We have examined the lattice vibrations and the energy landscape of the isoelectronic diamond and zincblende semiconductor series CuBr, ZnSe, GaAs, and Ge. Vibrations are found to be an increasing function of ionicity, with the cation sublattice always vibrating more strongly than the anion sublattice. These findings are consistent with density functional theory (DFT) calculations of the energy landscape and temperature-dependent molecular dynamics simulations of the atomic-position fluctuations. For CuBr, inclusion of the Cu $3d$ Hubbard $U$ term is found necessary to stabilize the zincblende structure and to bring its vibrational amplitudes into agreement with experiment. In addition, vibrations are found to strongly affect the CuBr near-edge x-ray absorption fine structure that we have successfully modeled by including displacements in our theoretical Bethe-Salpeter equation calculations. Reverse Monte Carlo structural refinements using large atomic configurations to simultaneously fit x-ray absorption and x-ray total-scattering data support these conclusions, and they reveal strong Cu-Br first-neighbor correlations and asymmetric distributions of interatomic distances in the temperature ranges of both negative and positive thermal expansion. Delineation of the CuBr valence band photoelectron spectrum into its Cu $3d$ and Br $4p$ states uniquely reveals their covalent mixing and further supports the DFT results.

Nanoscale quantum dots in microwave cavities can be used as a laboratory for exploring electron-electron interactions and their spin in the presence of quantized light and a magnetic field. We show how a simple theoretical model of this interplay at resonance predicts complex but measurable effects. New polariton states emerge that combine spin, relative modes, and radiation. These states have intricate spin-space correlations and undergo polariton transitions controlled by the microwave cavity field. We uncover novel topological effects involving highly correlated spin and charge density that display singlet-triplet and inhomogeneous Bell-state distributions. Signatures of these transitions are imprinted in the photon distribution, which will allow for optical read-out protocols in future experiments and nanoscale quantum technologies.

Ultrathin CrSBr flakes are exfoliated in situ on Au(111) and Ag(111) and their electronic structure is studied by angle-resolved photoemission spectroscopy. The thin flakes' electronic properties are drastically different from those of the bulk material and also substrate dependent. For both substrates, a strong charge transfer to the flakes is observed, partly populating the conduction band and giving rise to a highly anisotropic Fermi contour with an Ohmic contact to the substrate. The fundamental CrSBr band gap is strongly renormalized compared to the bulk. The charge transfer to the CrSBr flake is substantially larger for Ag(111) than for Au(111), but a rigid energy shift of the chemical potential is insufficient to describe the observed band structure modifications. In particular, the Fermi contour shows a Lifshitz transition, the fundamental band gap undergoes a transition from direct on Au(111) to indirect on Ag(111) and a doping-induced symmetry breaking between the intralayer Cr magnetic moments further modifies the band structure. Electronic structure calculations can account for nonrigid Lifshitz-type band structure changes in thin CrSBr as a function of doping and strain. In contrast to undoped bulk band structure calculations that require self-consistent $GW$ theory, the doped thin film properties are well approximated by density functional theory if local Coulomb interactions are taken into account on the mean-field level and the charge transfer is considered.

The interface traps and associated charge disorder in two-dimensional-material field-effect transitors (FETs), and many other devices, limits their performance but offers interesting physics and potential for applications. The electrical conductivity with gate-sweep in a few-layer ${\mathrm{MoS}}_2$-on-${\mathrm{SiO}}_2$ FET is found to show an abrupt reduction in hysteresis when cooled. The hysteresis and time-dependent conductivity of the ${\mathrm{MoS}}_2$ channel are modeled using the dynamics of interface traps' occupancy. The reduction in hysteresis is found to be steepest at a blocking temperature near 225 K. This is attributed to the interplay between thermal and barrier energies and fitted using a distribution of the latter. Further, the charge stored in the blocked traps at low temperature, and thus the threshold gate voltage, is reversibly programed over a wide range by cooling under suitable gate voltage. This illustrates the application of this blocking of traps for heat-assisted nonvolatile memory.

In phthalocyanine molecular conductors, the giant magnetoresistance effect is enhanced by the dilution of the localized-spin density. At low spin density, the localized spin induces a random potential for the conduction electron. The charge gap increases as spin density reaches intermediate levels. Analyses based on the mean-field theory and the exact-diagonalization method reveal that the ferrimagnetic charge-ordered state grows above the threshold localized-spin density. The localized spins assist in the ferromagnetic superexchange interaction, consistent with the measured spontaneous magnetization. Various electronic states compete with each other, and the coherent part of the optical conductivity is enhanced by the weak magnetic field. These theoretical findings are in stark agreement with the observed giant magnetoresistance.

Weyl fermions possess the property of spin-momentum locking: The expectation value of the spin is parallel or antiparallel to the momentum at any given point in the Brillouin zone in the vicinity of a Weyl node. This is a direct consequence of the fact that Weyl nodes are monopoles of the Berry curvature, and in this sense an expression of the nontrivial Weyl electronic structure topology. Owing to this property, an isolated Weyl node produces a large spin accumulation in response to a charge current, $\hslash /2$ per electron, similar to surface states of time-reversal-invariant topological insulators. However, in bulk Weyl semimetals, the nodes must occur in pairs of opposite chirality and, when the nodes are at the same energy, the effect cancels out. Here, we show that this cancellation is avoided in chiral semimetals, in which Weyl nodes of opposite chirality occur at different energies due to broken mirror symmetry. We find that the spin accumulation is maximized when the Fermi energy coincides with one of the nodes in a pair and reaches the same value as for an isolated node in this case. Moreover, we demonstrate the existence of a distinct magnetoresistance mechanism, closely related to this current-induced spin accumulation.

In planar microcavities, the transverse-electric and transverse-magnetic (TE-TM) mode splitting of cavity photons can result in optical spin-orbit coupling (SOC). In this work, we find that in a liquid crystal (LC) microcavity filled with perovskite microplates, the pronounced TE-TM splitting gives rise to a strong SOC that leads to the spatial instability of microcavity polariton condensates under single-shot excitation. Spatially varying hole burning occurs between polarization components leading to different condensate profiles from shot to shot. The single-shot polariton condensates become stable when the SOC vanishes as the TE and TM modes are spectrally well separated from each other, which can be achieved by application of an electric field to our LC microcavity with electrically tunable anisotropy. Our findings are well reproduced and traced back to their physical origin by our detailed numerical simulations. With the electrical manipulation our work reveals how the shot-to-shot spatial instability of spatial polariton profiles can be engineered in anisotropic microcavities at room temperature, which will benefit the development of stable polariton-based optoeletronic and light-emitting devices.

The mutual competition and synergy of magnetism and superconductivity provide us with a very valuable opportunity to access topological superconductivity and Majorana fermions. Here, we devise a heterostructure consisting of an $s$-wave superconductor, a two-dimensional topological insulator, and an altermagnet, which is classified as the third magnet and featured by zero magnetization but spin polarization in both real and reciprocal spaces. We find that the altermagnet can induce mass terms at the edges that compete with electron pairing, and mass domains are formed at the corners of the sample, resulting in zero-energy Majorana corner modes (MCMs). The presence or absence of MCMs can be engineered by only changing the direction of the Néel vector. Moreover, uniaxial strain can effectively manipulate the patterns of the MCMs, such as moving and interchanging MCMs. Experimental realization, remarkable advantages of our proposal, and possible braiding are discussed.

Higher-order topological insulators (HOTIs) have emerged as unique topological materials hosting topological corner or hinge states. This work investigates terahertz (THz) higher-order topological states in $C_3$ symmetric valley photonic crystals (VPCs) in theory and experiment. Based on numerical simulations of photonic band structure, phase profiles, and Berry curvature, we realize the valley topological phase transition by rotating the scatterers in unit cells. Meanwhile, the higher-order topology of the VPCs is characterized by nontrivial bulk polarization. The topological corner states are demonstrated by calculated eigenenergy spectra, field distributions, and local density of states of nested triangular structures. In addition, the associated fractional corner charge is also employed to confirm the existence of topological corner states directly. Two topological corner states are identified, one staying within band gap and the other embedding in bulk bands. Both originate from quantized bulk dipole moments and are flexibly switchable by rotating the scatterers of the system. Experimentally angle-resolved transmittance measurements demonstrate the presence of the photonic band structure and the bulk band gap of the THz photonic crystals. The measured time-domain spectra reveal the valley edge states between distinct THz VPCs. Further, we directly observe the topological corner states in the measured spatial mapping of the electric field intensity. These investigations testify to the possibility of simultaneously employing topological corner, edge, and bulk states to guide THz waves, which may have potential applications in THz functional devices.