We report the static and dynamic magnetic properties of ${\mathrm{LaSrCrO}}_4$, a seemingly canonical spin-3/2 square-lattice antiferromagnet that exhibits frustration between magnetic layers—owing to their AB stacking—and offers a rare testbed to investigate accidental-degeneracy lifting in magnetism. Neutron diffraction experiments on single-crystal samples uncover a remarkable anticollinear magnetic order below $T_N$ = 170 K characterized by a Néel arrangement of the spins within each layer and an orthogonal arrangement between adjacent layers. To understand the origin of this unusual magnetic structure, we analyze the spin-wave excitation spectrum by means of inelastic neutron scattering and bulk measurements. A spectral gap of 0.5 meV, along with a spin-flop transition at 3.2 T, reflect the energy scale associated with the degeneracy-lifting. A minimal model to explain these observations requires both a positive biquadratic interlayer exchange and dipolar interactions, both of which are on the order of 10${}^{-4}$ meV, only a few parts per million of the dominant exchange interaction $J_1\approx 11$ meV. These results provide direct evidence for the selection of a noncollinear magnetic structure by the combined effect of two distinct degeneracy lifting interactions.

We investigate the quantization of the complex-valued Berry phases in non-Hermitian quantum systems with certain generalized symmetries. In Hermitian quantum systems, the real-valued Berry phase is known to be quantized in the presence of certain symmetries, and this quantized Berry phase can be regarded as a topological order parameter for gapped quantum systems. In this Letter, on the other hand, we establish that the complex Berry phase is also quantized in the systems described by a family of non-Hermitian Hamiltonians. Let $H\left(\theta \right)$ be a non-Hermitian Hamiltonian parametrized by $\theta$. Suppose that there exists a unitary and Hermitian operator $P$ such that $PH\left(\theta \right)P=H(-\theta )$ or $PH\left(\theta \right)P=H^{†}(-\theta )$. We prove that in the former case, the complex Berry phase $\gamma$ is ${\mathbb{Z}}_2$ quantized, whereas in the latter, only the real part of $\gamma$ is ${\mathbb{Z}}_2$ quantized. The operator $P$ can be viewed as a generalized symmetry operation for $H\left(\theta \right)$, and, in practice, $P$ can be, for example, a spatial inversion. Our results are quite general and apply to both interacting and noninteracting systems. We also argue that the quantized complex Berry phase is capable of classifying non-Hermitian topological phases and demonstrate this in one-dimensional many-body systems with and without interactions.

Surface bound states in the continuum (SBICs) have been found to occur in diverse settings, but so far always at the interface of nonhomogeneous media, such as discrete lattices or periodic systems. Here, we show that they can also exist at the interface of homogeneous media, resulting in unique SBICs. Specifically, we found that, contrary to general belief, leaky Dyakonov states exist at the interface between materials that exhibit opposite signs of anisotropy. In addition, properly breaking the anisotropy symmetry leads to the formation of both guided states and also SBICs embedded within the continuum. A direct implication of our finding is the possibility to create SBICs and Dyakonov states in a whole new class of materials and metamaterials.

Modern laboratory techniques such as ultrafast laser excitation and shock compression can bring matter into highly nonequilibrium states with complex structural transformation, metallization, and dissociation dynamics. To understand and model the dramatic change of both electronic structures and ion dynamics during such dynamic processes, the traditional method faces difficulties. Here, we demonstrate the ability of a deep neural network (DNN) to capture the atomic local-environment dependence of the electronic density of states (DOS) for both multicomponent systems under exoplanet thermodynamic conditions and nonequilibrium systems during superheated melting processes. Large-scale and time-resolved diagnosis of DOS can be efficiently achieved within the accuracy of the ab initio method. Moreover, the atomic contribution to DOS given by the DNN model accurately reveals the information of the local neighborhood for the selected atom, which thus can serve as robust order parameters to identify different phases and intermediate local structures, strongly highlighting the efficacy of this DNN model in studying dynamic processes.

A major open topic in cuprates is the interplay between the lattice and electronic dynamics and the importance of their coupling to the mechanism of high-temperature superconductivity (HTSC). As evidenced by extended x-ray absorption fine structure (EXAFS) experiments, anharmonic structural effects are correlated with the charge dynamics and the transition to a superconducting phase in different HTSC compounds. Here we describe how structural anharmonic effects can be coupled to electronic and lattice dynamics in cuprate systems by performing the exact diagonalization of a prototype anharmonic many-body Hamiltonian on a relevant 6-atom cluster and show that the EXAFS results can be understood as a Kuramoto synchronization transition between coupled internal quantum tunneling of polarons associated with the two-site distribution of the copper–apical oxygen ($\mathrm{Cu}\text{−}{\mathrm{O}}_{\mathrm{ap}}$) pair in the dynamic structure. The transition is driven by the anharmonicity of the lattice vibrations and promotes the pumping of charge, initially stored at the apical oxygen reservoirs, into the copper-oxide plane. Simultaneously, a finite projection of the internal quantum tunneling polaron extends to the copper–planar oxygen ($\mathrm{Cu}\text{−}{\mathrm{O}}_{\mathrm{pl}}$) pair. All these findings allow an interpretation based on an effective quantum-mechanical triple-well potential associated with the oxygen sites of the 6-atom cluster, which accurately represents the phase synchronization of apical oxygens and lattice-assisted charge transfer to the ${\mathrm{CuO}}_2$ plane.

We investigate the effect of spin-lattice coupling (SLC) on the magnetic properties of the classical kagome-lattice Heisenberg antiferromagnet (KHAF) using improved Monte Carlo updates. The lattice modes are represented by Einstein site phonons, which introduce effective further-neighbor spin interactions in addition to the nearest-neighbor biquadratic interactions. In the weak SLC, the macroscopically degenerate coplanar ground state remains at zero field, while a $\sqrt{3}\times \sqrt{3}$ ordered phase accompanied by a 1/3-magnetization plateau appears in external magnetic fields. In the strong SLC, we find a nematic order at zero field and a 1/9-magnetization plateau associated with a $3\times 3$ collinear order. Near the phase transition between the 1/9- and 1/3-plateau states, the ergodicity in the single spin flip is practically broken, and slow dynamics appear. We propose that relevant KHAFs with strong SLC would be realized in spinel-based materials.

Josephson radiation is a useful signature for detecting Majorana zero modes in topological superconductors. We study the Josephson radiation of the underdamped topological Josephson junction within the quantum resistively and capacitively shunted junction model. We show that the quantum dynamics of the Majorana two-level system induce oscillatory patterns in the Josephson emission spectra. With the Floquet method, we obtain analytical results for these oscillatory patterns and find that they are well described by Bessel functions. We perform numerical simulations to verify the analytical results and demonstrate that these Bessel radiation patterns exist for a wide range of junction parameters.

Full Heusler compounds have become a research hotspot in the thermoelectric (TE) field, because they have the remarkable electronic properties and high-TE power factor. Nevertheless, the inherent high thermal conductivity ${\kappa }_L$ hinders their further application as TE device. Hence, we investigate the mechanical, transport, and thermoelectric properties in ${\mathrm{Na}}_2\mathrm{KSb}$ and ${\mathrm{X}}_2\mathrm{CsSb}$ (X = K, Rb) with eight valence electrons per formula unit (f.u.) by using the first-principles calculations combined with self-consistent phonon (SCP) theory, compressive sensing (CS) techniques, and Boltzmann transport equation (BTE). Due to the strong three phonon scattering combined with small phonon group velocity, we obtain the ultralow lattice thermal conductivities. An evaluation of their mechanical properties reveals that they are all brittle compounds, and ${\mathrm{Rb}}_2\mathrm{CsSb}$ has the strongest elastic anisotropy. To capture rational electron transport properties, we include the effects of the acoustic deformation potential (ADP) scattering, polar optical phonon (POP) scattering, and ionized impurity (IMP) scattering on the electron relaxation time. Finally, a high p-type $\mathit{ZT}$ values of 2.74 (2.48) at 600 (900) K are captured in the cubic ${\mathrm{K}}_2\mathrm{CsSb}$ $\left({\mathrm{Na}}_2\mathrm{KSb}\right)$. These findings not only help us to comprehensively understand the physical properties of full Heusler compounds with eight valence electrons per f.u., but also support them as potential candidates for thermal management and thermoelectric applications.

The significance of spin transport over an interface in energy-efficient spintronic devices has stimulated interest in the spintronic society during the last few decades. Here, interfaces of $\text{permalloy}/{\mathrm{Cu}}_{1-x}{\mathrm{Tb}}_x$ (Py/Cu-Tb) were investigated in depth. As the Cu-Tb thickness increases, we found that the saturation magnetization of the bilayers falls and then plateaus. Element-specific x-ray magnetic circular dichroism studies suggest that the Tb moment aligns opposite to the Fe and Ni moments, forming a self-assembled antiferromagnetic interface. As a result, the Cu-Tb adjacent layer to Py and the interface have a significant impact on spin transport. Relevant parameters, such as spin mixing conductance, spin diffusion length, and damping, can be tuned by inserting a thin Cu layer between Py and Tb or varying the compositions of Cu-Tb alloys. Using rare-earth Tb, we provide an effective method for controlling the spin transport and magnetism of ferromagnet/normal-metal interfaces. This approach is expected to have a great deal of potential in spintronic applications.

We investigate the physics of an adiabatic transition from a BCS superconductor to a Fermi liquid for an exponentially slow decreasing pairing interaction. We show that, depending on the order of the thermodynamic limit and large times, a situation can arise in which the Fermi liquid keeps a memory of the parent BCS state. Furthermore, a time inversion of the interaction, supplemented by a manipulation analogous to a spin-/photon-echo experiment, allows us to recover the parent BCS state. Moreover, we study the evolution of the order parameter phase $\varphi$ in transforming the BCS superconductor to a conventional metal. Since the global phase is the conjugate variable of the density, we explicitly show how to use the dynamics of $\varphi$ together with gauge invariance to build up the noninteracting chemical potential away from particle-hole symmetry. We further analyze the role of $\varphi$ in restoring the gauge-invariant current response when the noninteracting Fermi liquid is approached starting from a BCS superconductor in the presence of an external vector field.

The study of topological states in electric circuits is developing rapidly recently and forming the field of topoelectrical circuits. As both the loss and gain can be easily introduced and tuned in electric circuits, it permits flexible and accurate fabrications of non-Hermitian systems. Loss is generally considered negative in electric circuits, as it weakens the electrical signals. However, we show here that a non-Hermitian second-order topological phase can be realized in electric circuits by taking advantage of loss. We observe the gapped edge states and in-gap corner states in experiment. Our system provides a readily accessible platform to explore the non-Hermitian-induced topological phases.

Electronic properties of palladium-silver alloys have been studied for almost a century as a prototype of a transition-metal alloy with entangled $s$ and $d$ bands. We review the literature starting from Mott's model of 1935 and discuss from a quantitative point of view a series of common assumptions stemming from that seminal paper. We also show that spectral functions obtained by unfolding the band structures of a sample of supercells can be used for the ab initio computation of the thermopower of such systems within a Boltzmann transport equation approach.

The discovery of the quantization of particle transport in adiabatic pumping cycles of periodic structures by Thouless [Phys. Rev. B 27, 6083 (1983).] linked the Chern number, a topological invariant characterizing the quantum Hall effect in two-dimensional electron gases, with the topology of dynamical periodic systems in one dimension. Here we demonstrate its counterpart for higher-order topology. Specifically, we show that adiabatic cycles in two-dimensional crystals with vanishing dipole moments (and therefore zero overall particle transport) can nevertheless be topologically nontrivial. These cycles are associated with higher-order topology and can be diagnosed by their ability to produce corner-to-corner transport in certain metamaterial platforms. We experimentally verify the corner to corner transport associated with this topological pump by using an array of photonic waveguides adiabatically modulated in their separations and refractive indices. By mapping the dynamical phenomenon demonstrated here from two spatial and one temporal dimensions to three spatial dimensions, our observations are equivalent to the observation of chiral hinge states in a three-dimensional second-order topological insulator.

Edge magnetism in zigzag transition metal dichalcogenide nanoribbons is studied using a three-band tight-binding model with local electron-electron interactions. Both mean field theory and the unbiased, numerically exact determinant quantum Monte Carlo method are applied. Depending on the edge filling, mean field theory predicts different phases: gapped spin dimer and antiferromagnetic phases appear for two specific fillings, with a tendency towards metallic edge-ferromagnetism away from those fillings. Determinant quantum Monte Carlo simulations confirm the stability of the antiferromagnetic gapped phase at the same edge filling as mean field theory, despite being sign-problematic for other fillings. The obtained results point to edge filling as yet another key ingredient to understand the observed magnetism in nanosheets. Moreover, the filling dependent edge magnetism gives rise to spin-polarized edge currents in zigzag nanoribbons which could be tuned through a back gate voltage, with possible applications to spintronics.

This paper is a computational investigation of the electronic band gap and optical properties of ${\mathrm{SnS}}_2$ and $3d$-series transition metal doped ${\mathrm{SnS}}_2$ systems. The ${\mathrm{SnS}}_2$ crystal is a nonmagnetic indirect band gap semiconductor both in bulk and in the monolayer limit. The transition metal substitution at Sn site induces magnetism inside the crystal. Therefore studying its doping by $3d$-series transition metals is essential from an application perspective. We use the dielectric-dependent hybrid functionals of ab initio calculations for computing the electronic band gap. The dielectric-dependent hybrid computations rely on the electronic static dielectric constant. In these calculations, we iteratively update the dielectric constant and exchange parameter from one another until the convergence. As a result, we present a range of possible band gap values. Specifically, we determine the lower and upper bounds of possible experimental band gap values for all these doped systems. Further, we explore the optical properties of each doped system in the monolayer and bulk forms. We discuss the absorption spectra, optical constants, and exciton binding energy of all the doped systems. We conclude that the transition metal doped ${\mathrm{SnS}}_2$ is a good candidate for optoelectronic device applications.

Strong coupling exhibits the unique ability to preserve quantum sates between light and matter, which is essential for the development of quantum information technology. To explore the physical mechanism behind this phenomenon, we employ the tight-binding method for expanding the temporal coupled-mode theory, with the absorption spectrum formula of coupled system directly obtained in an analytical way. It reveals all the physical meaning of parameters defined in our theory and shows how to tailor line shapes of the coupled systems. Here we set an example to manipulate the strong coupling in a hybrid structure composed of excitons in monolayer ${\mathrm{WS}}_2$ and quasibound states in the continuum supported by the ${\mathrm{TiO}}_2$ nanodisk metasurfaces. The simulated results show that a clear spectral splitting appeared in the absorption curve, which can be controlled by adjusting the asymmetric parameter of the nanodisk metasurfaces and well fitted through our theoretical predictions. Our work not only gives a more comprehensive understanding of such coupled systems but also offers a promising strategy in controlling strong light–matter coupling to meet diversified application requests.

Chromium triiodide is an intrinsically magnetic van der Waals material down to the single-layer limit. Here, we provide a first-principles description of finite-temperature magnetic and spectral properties of monolayer (ML) ${\mathrm{CrI}}_3$ based on fully charge self-consistent density functional theory (DFT) combined with dynamical mean-field theory, revealing a formation of local moments on Cr from strong local Coulomb interactions. We show that the presence of local dynamical correlations leads to a modification of the electronic structure of ferromagnetically ordered ${\mathrm{CrI}}_3$. In contrast to conventional $\mathrm{DFT}+U$ calculations, we find that the top of the valence band in ML ${\mathrm{CrI}}_3$ demonstrates essentially different orbital character for minority and majority spin states, which is closer to the standard DFT results. This leads to a strong spin polarization of the optical conductivity upon hole doping, which could be verified experimentally.

We demonstrate the universal properties of dissipative Tomonaga-Luttinger (TL) liquids by calculating correlation functions and performing finite-size scaling analysis of a non-Hermitian XXZ spin chain as a prototypical model in one-dimensional open quantum many-body systems. Our analytic calculation is based on effective field theory with bosonization, finite-size scaling approach in conformal field theory, and the Bethe-ansatz solution. Our numerical analysis is based on the density-matrix renormalization group generalized to non-Hermitian systems (NH-DMRG). We uncover that the model in the massless regime with weak dissipation belongs to the universality class characterized by the complex-valued TL parameter, which is related to the complex generalization of the $c=1$ conformal field theory. As the dissipation strength increases, the values of the TL parameter obtained by the NH-DMRG begin to deviate from those obtained by the Bethe-ansatz analysis, indicating that the model becomes massive for strong dissipation. Our results can be tested with the two-component Bose-Hubbard system of ultracold atoms subject to two-body loss.