Magnetic rare-earth monopnictides have attracted a great deal of interest, not only because of the nontrivial topological electronic states but also due to the extremely large magnetoresistance. In this paper, we report the angular-dependent magnetization and magnetoresistance of the antiferromagnetic topological semimetal HoSb. At elevated temperatures, the angular magnetoresistance displays minima and maxima around $n\pi /2$ and $\left(2n+1\right)\pi /4$ ($n=0$, 1, 2, and 3), respectively. At low temperatures (<∼6 K), both the magnetoresistance and magnetization showcase strong angular dependence. Different from those of other rare-earth monopnictides, HoSb's angular magnetoresistance exhibits extra minima between $n\pi /2$ and $\left(2n+1\right)\pi /4$, and between $\left(2n+1\right)\pi /4$ and $\left(n+1\right)\pi /2$ ($n=0$, 1, 2, and 3), around which the magnetic phase transitions from ferromagnetic to HoP-type antiferromagnetic state, and from HoP-type antiferromagnetic to ferromagnetic state occur, suggesting the close interplay between conduction electrons and magnetism. Several possible causes have been carefully discussed for these unexpected phenomena. Our findings reveal the crucial role of magnetization anisotropy on the angular magnetoresistance in magnetic rare-earth monopnictides, and may provide a paradigm for studying the magnetization control of magnetoresistance anisotropy in other magnetic semimetals.

Using the self-consistent Born approximation, we study a topological phase transition appearing in bulk HgCdTe crystals induced uncorrelated disorder due to both randomly distributed impurities and fluctuations in Cd composition. By following the density-of-states evolution, we clearly demonstrate the topological phase transition, which can be understood in terms of the disorder-renormalized mass of Kane fermions. We find that the presence of a heavy-hole band in HgCdTe crystals leads to the topological phase transition at much lower disorder strength than is expected for conventional three-dimensional topological insulators. Our theoretical results can also be applied to other narrow-gap zinc-blende semiconductors such as InAs, InSb, and their ternary alloys InAsSb.

We review three different approaches for the calculation of electromagnetic multipoles, namely, the Cartesian primitive multipoles, the Cartesian irreducible multipoles, and the spherical multipoles. We identify the latter as the best suited to describe the scattering of electromagnetic radiation, as exemplified for an amorphous silicon sphere. These multipoles are then used to calculate the optical force acting on semiconductor, dielectric or metallic particles in a wide wavelength range, from the dipolar regime down to the Mie regime.

Band inversion is a known feature in a wide range of topological insulators characterized by a change of orbital type around a high-symmetry point close to the Fermi level. In some cases of band inversion in topological insulators, the existence of quasinodal spheres has been detected, and the change of orbital type is shown to be concentrated along these spheres in momentum space. To understand this phenomenon, we develop a local effective fourfold Hamiltonian that models the band inversion and reproduces the quasinodal sphere. This model shows that the signal of the spin Hall conductivity, as well as the change of orbital type, are both localized on the quasinodal sphere, and moreover, that these two indicators characterize the topological nature of the material. Using K-theoretical methods, we show that the change of orbital type parametrized by an odd clutching function is equivalent to the strong Fu-Kane-Mele invariant. We corroborate these results with ab initio calculations for the materials ${\mathrm{YH}}_3$ and CaTe, where in both cases the signal of the spin Hall conductivity is localized on the quasinodal spheres in momentum space. We conclude that a nontrivial spin Hall conductivity localized on the points of change of orbital type is a good indicator for topological insulation.

van der Waals materials such as ${\mathrm{NbSe}}_2$ or ${\mathrm{TaS}}_2$ have demonstrated Ising superconductivity down to atomically thin layers. Due to the spin-orbit coupling, these superconductors have an in-plane upper critical magnetic field far beyond the Pauli limit. We theoretically demonstrate that twisted bilayer Ising superconductors separated by a ferromagnetic buffer layer can naturally host chiral topological superconductivity with Chern numbers, which can be realized in heterostructures such as ${\mathrm{NbSe}}_2/{\mathrm{CrCl}}_3/{\mathrm{NbSe}}_2$. Under appropriate experimental conditions the topological superconducting gap can reach $>0.1\mathrm{meV}$, leading to readily observable signatures such as quantized thermal Hall transport at low temperatures.

Novel two-dimensional electron systems at the interfaces and surfaces of transition-metal oxides recently have attracted much attention as they display tunable, intriguing properties that can be exploited in future electronic devices. Here we show that a high-mobility quasi-two-dimensional electron system with strong spin-orbit coupling can be induced at the surface of a ${\mathrm{KTaO}}_3$ (001) crystal by pulsed laser deposition of a disordered ${\mathrm{LaAlO}}_3$ film. The momentum-resolved electronic structure of the buried electron system is mapped out by hard x-ray angle-resolved photoelectron spectroscopy. From a comparison to calculations, it is found that the band structure deviates from that of electron-doped bulk ${\mathrm{KTaO}}_3$ due to the confinement to the interface. Fermi surface mapping shows a three-dimensional, periodic intensity pattern consistent with electron pockets of quantum well states centered around the $\mathrm{\Gamma }$ points and the expectations from a Fourier analysis-based description of photoemission on confined electron systems. From the $k$ broadening of the Fermi surface and core-level depth profiling, we estimate the extension of the electron system to be at least 1 nm but not much larger than 2 nm, respectively.

Single-atom-thick two-dimensional (2D) materials such as graphene usually have a hexagonal lattice while the square-planar lattice is uncommon in the family of 2D materials. Here, we demonstrate that single-atom-thick transition metal nitride ${\mathrm{CrN}}_4$ monolayer is a stable free-standing layer with a square-planar network. The stability of square-planar geometry is ascribed to the combination of N=N double bond, Cr-N coordination bond, and $\pi -d$ conjugation, in which the double $\pi -d$ conjugation is rarely reported in previous studies. This mechanism is entirely different from that of the reported 2D materials, leading to lower formation energy and more robust stability than the synthesized $g-{\mathrm{C}}_3{\mathrm{N}}_4$ monolayer. On the other hand, the ${\mathrm{CrN}}_4$ layer has a ferromagnetic (FM) ground state, in which the FM coupling between two Cr atoms is mediated by electrons of the half-filled large $\pi$ orbitals from $\pi -d$ conjugation. The high-temperature ferromagnetism in ${\mathrm{CrN}}_4$ monolayer is confirmed by solving the Heisenberg model with the Monte Carlo method.

We develop an efficient and general method to determine the Hofstadter spectrum of isolated narrow bands. The method works for topological as well as for trivial narrow bands by projecting the zero $\mathbf{B}$-field hybrid Wannier states—which are localized in one direction and Bloch extended in another direction—onto a representation of the magnetic translation group in the Landau gauge. We then apply this method to find the Hofstadter spectrum for the exact single-particle charged excitations in the strong-coupling limit of the magic angle twisted bilayer graphene at the charge neutrality point and at $\left|\nu \right|=2$ down to low magnetic fields when the flux through the moiré unit cell is only $\sim 1/25$ of the electronic flux quantum, i.e., $\sim 1\mathrm{T}$ at the first magic angle. The resulting spectra provide a means to investigate Landau quantization of the quasiparticles even if their dispersion is interaction induced.

We study the stability of nonergodic but extended (NEE) phases in non-Hermitian systems. For this purpose, we generalize the so-called Rosenzweig-Porter random-matrix ensemble, known to carry a NEE phase along with the Anderson localized and ergodic ones, to the non-Hermitian case. We analyze, both analytically and numerically, the spectral and multifractal properties of the non-Hermitian case. We show that the ergodic and localized phases are stable against the non-Hermitian nature of matrix entries. However, the stability of the fractal phase depends on the choice of the diagonal elements. For purely real or imaginary diagonal potential, the fractal phase is intact, while for a generic complex diagonal potential the fractal phase disappears, giving way to a localized one.

Effective modeling of magnetization dynamics is key to understanding the nature of exotic magnetic structures and behaviors such as magnetic skyrmions and spin waves. Although the modeling of magnitude variation of magnetizations is crucial for magnets at finite temperatures (especially near the Curie temperature with the precursor effect), it is restrained in common micromagnetic simulations. Here, we propose an effective methodology for modeling the magnitude-fluctuated magnetization dynamics based on Ginzburg-Landau theory, which includes both the precession motion and adjustable magnitude of magnetizations simultaneously. Our model includes the intrinsic synergy of precession motion and adjustable magnitude of magnetizations, i.e., dynamic precursor effect. Therefore, in this paper, we provide an advanced simulation methodology and introduce an intrinsic dynamic modulation in magnetic system, which is anticipated to be a starting point for the future study of the dynamics of magnetization, magnetic domains, and topologies in magnets.

The electromagnetic response of type-II superconductors exposed to a magnetic field is governed by the dynamics of the vortex matter. We found that there exists a force of non-Peach-Köhler type which acts on edge dislocations in vortex lattices and depends on the gradients of vortex density. This force is absent in atomic solids where the density of the crystal lattice is constant even in the presence of dislocations. By mapping the classic theory of dislocations onto vortex lattices, we find the critical current $j_c^{\text{pl}}$ and the activation energy $U_{\text{pl}}$ associated with the dislocation-mediated plastic creep. The latter proves to decrease with magnetic field as $B^{-3/4}$, in concordance with experimental data. Such behavior of $U_{\text{pl}}$ is just opposite to the case of elastic (collective) creep, where $U_{\text{el}}$ always grows with $B$. At high enough field $U_{\text{pl}}$ becomes less than $U_{\text{el}}$, thus plastic creep overwhelms the elastic one and becomes the dominant mechanism of vortex mobility. This explains the appearance of the “fishtail” (double-peak) shape of magnetization curves in high-$T_c$ superconductors.

In strong-coupling regimes, quantum dynamical effects can alter conventional physics described by perturbation theories, but the dynamical simulations of these quantum systems using matrix product states—such as multilevel vibronic systems that are relevant to energy and electron transfer reactions—suffer from rapid entanglement growth during their real-time evolution, impeding explorations of spectra, dynamics, and kinetics. We examine the possibility of using nonunitary transformations to alter dynamical entanglement growth in matrix-product-state simulations of quantum systems, using the spin-boson model to showcase the reduced entanglement. By appropriately choosing the transformation, the entanglement growth rate is suppressed, improving the efficiency of quantum dynamical simulations. Entanglement control is achieved by the transformation-induced biased transitions among the system quantum states, and by “projecting” (approximately) the system quantum state to one of the eigenstates of the system-bath coupling operator, thus controlling the energy exchange between the system and the bath. The transformation can be applied to quantum many-body systems, including spin chains and multilevel vibronic systems; the approach improves the numerical efficiency of the matrix product state simulations.

Thin ferromagnetic films can possess unconventional magnetic properties, opening a new road for using them in spintronic technologies. In the present work exploiting three different methods, we comprehensively analyze phason excitations of a skyrmion lattice in synthetic antiferromagnets. To analyze phason excitations of the skyrmion lattice, we have constructed an analytical model based on three coupled helices and found a linear gapless mode. Micromagnetic simulations also support this result. Moreover, a similar result has been achieved within the rigid skyrmion lattice model based on the coupled Thiele's equations, when the coupling between skyrmions in different layers of the synthetic antiferromagnetic is comparable to or larger than the intralayer coupling. In addition, we also consider the orbital angular momentum and spin pumping current associated with phason excitations. Due to the gapless excitations in the case of skyrmion lattice, the pumping current is nonzero for the arbitrary frequency of pumping microwaves. In the case of individual skyrmions, no current is pumped when microwave frequency is inside the gap of the spectrum of individual skyrmions.

The evolution of fine electronic structures in superconducting $\mathrm{Ln}{\mathrm{O}}_{1-x}{\mathrm{F}}_x\mathrm{Bi}{\mathrm{S}}_2$ (Ln denotes lanthanoid) is systematically investigated with spin- and angle-resolved photoemission spectroscopy. A shape change of the Fermi surface (FS) at the $X$ point from elliptical to rectangular with increasing the electron doping is commonly observed in different lanthanide systems. Besides that, an emergent large Fermi surface around the Г point is also observed in all the samples with different doping levels deviating from the theoretical prediction, which might be related to the superconductivity. In addition, we found a humped band around $X$(π,0) in the highly doped samples only, which may be attributed to the ${\mathrm{BiS}}_2$ surface reconstruction or surface defects relying on the electron concentration. We also demonstrate the spin-selective excitation of photoelectrons, which indicates the presence of spin-orbital-entangled bulk Rashba splitting in this system. This result may enable the optical tuning of electron spin in a ${\mathrm{BiS}}_2$-based system.

The kagome lattice offers unique opportunities for the exploration of unusual quantum states of correlated electrons. Here, we report on the observation of superconductivity in a kagome single-crystal ${\mathrm{Pd}}_3{\mathrm{P}}_2{\mathrm{S}}_8$ when a semiconducting-to-metallic transition is driven by pressure. High-pressure resistance measurements show that the metallization and superconductivity are simultaneously observed at about 11 GPa. With increasing pressure, the superconducting critical temperature $T_c$ is monotonously enhanced from 2.6 K to a maximum 7.7 K at $\sim 52\mathrm{GPa}$. Interestingly, superconductivity is retained when the pressure is fully released. Synchrotron x-ray diffraction and Raman experiments consistently evidence that the emergence of superconductivity is accompanied with an amorphization, and the retainability of superconductivity upon decompression can be attributed to the irreversibility of the amorphization.

Metallic spin liquid has been reported in several correlated metals, but a satisfactory theoretical description is not yet available. Here we propose a potential route to realize the metallic spin liquid and construct an effective ${\mathbb{Z}}_2$ gauge theory with charged fractionalized excitations on the triangular Kondo lattice. This leads to a ${\mathbb{Z}}_2$ metallic spin liquid featured with long-lived, heavy holon excitations of spin 0 and charge $+e$ and a partially enlarged electron Fermi surface. It differs from the weak-coupling ${\mathrm{FL}}^{*}$ state proposed earlier and may be viewed as a fractionalized heavy fermion liquid. Our theory provides a general framework to describe the metallic spin liquid in frustrated Kondo lattice systems.

Topological insulators, which are insulating in the bulk and conducting on the surface, have attracted great interest in recent years. The recently discovered topological surface and hinge states in three dimensions have provided promising methods for wave manipulation in classical systems. However, the combination of surface states and interface states has yet to be achieved in phononic crystals due to the missing topological surface states. Here, we experimentally demonstrate a fragile topological insulator with a bilayer kagome lattice. We observe the surface states in three different orientations and interface states formed by inversion of layer pseudospin sectors or bands. The combination of surface and interface states is investigated in $\mathsf{X}$-shaped waveguides. Our work may provide a platform for exploring unique acoustic applications based on surface or interface states.

We present a formalism for studying the radiation-matter interaction in multilayered dielectric structures with active semiconductor quantum wells patterned with an in-plane periodic lattice. The theory is based on the diagonalization of the generalized Hopfield matrix, and it includes loss channels in a non-Hermitian formulation. Hybrid elementary excitations named photonic crystal polaritons arise in these systems, whose detailed dispersion and loss characteristics are shown to depend on material composition as well as on symmetry properties of the lattice. We show the generality of the approach by calculating polariton dispersions in very diverse material platforms, such as multilayered perovskite-based lattices or inorganic semiconductor heterostructures. As an application of the method, we show how to engineer lossless polariton modes through excitonic coupling to bound states in the continuum at either zero or finite in-plane wave vector, and discuss their topological properties. Detailed comparison with a semiclassical approach based on the scattering matrix method is provided, which allows to interpret the optical spectra in terms of polarization-dependent excitation of the different polariton branches. This paper introduces an efficient and invaluably versatile numerical approach to engineer photonic crystal polaritons, with potential applications ranging from low-threshold lasers to symmetry-protected propagating modes of hybrid radiation-matter states.

First-principles scattering calculations are used to investigate spin transport through interfaces between diffusive nonmagnetic metals where the symmetry lowering leads to an enhancement of the effect of spin-orbit coupling and to a discontinuity of the spin currents passing through the interfaces. From the conductance and local spin currents calculated for nonmagnetic bilayers, we extract values of the room-temperature interface resistance $R_{\mathrm{I}}$, of the spin memory-loss parameter $\delta$, and of the interface spin Hall angle ${\mathrm{\Theta }}_{\mathrm{I}}$ for nonmagnetic $\mathrm{Au}|\mathrm{Pt}$ and $\mathrm{Au}|\mathrm{Pd}$ interfaces using a frozen thermal disorder scheme to model finite temperatures. Substantial values of all three parameters are found with important consequences for experiments involving nonmagnetic spacer and capping layers. The temperature dependence of the interface parameters is determined for $\mathrm{Au}|\mathrm{Pt}$.

We utilize Bardeen's tunneling theory to calculate intra and interorbital hopping integrals between phosphorus donors in silicon using known orbital wave functions. While the two-donor problem can be solved directly, the knowledge of hoppings for various pairs of orbitals is essential for constructing multi-orbital Hubbard models for chains and arrays of donors. To assure applicability to long-range potentials, we rederive Bardeen's formula for the matrix element without assuming nonoverlapping potentials. Moreover, we find a correction to the original expression allowing us to use it at short distances. We also show that accurate calculation of the lowest donor-pair eigenstates is possible based on these tunnel couplings and we characterize the obtained states. The results are in satisfactory quantitative agreement with those obtained with the standard Hückel tight-binding method. The calculation relies solely on the wave functions in the barrier region and does not explicitly involve donor or lattice potentials, which has practical advantages. We find that neglecting the central correction potential in the standard method may lead to qualitatively incorrect results, while its explicit inclusion raises severe numerical problems, as it is contained in a tiny volume. In contrast, using wave functions obtained with this correction in the proposed method does not raise such issues. Nominally, the computational cost of the method is to calculate a double integral along the plane that separates donors. For donor separation in directions where valley interference leads to oscillatory behavior, additional averaging over the position of the integration plane is needed. Despite this, the presented approach offers a competitive computational cost as compared to the standard one. This work may be regarded as a benchmark of a promising method for calculating hopping integrals in lattice models with known or postulated orbital wave functions.