The quantum anomalous Hall (QAH) effect, with its single chiral, topologically protected edge state, offers a platform for flying Majorana states as well as nonreciprocal microwave devices. While recent research showed the nonreciprocity of edge plasmons in Cr-doped ${\left({\text{Bi}}_x{\text{Sb}}_{1-x}\right)}_2{\text{Te}}_3$, the understanding of their dissipation remains incomplete. Our study explores edge plasmon dissipation in V-doped ${\left({\text{Bi}}_x{\text{Sb}}_{1-x}\right)}_2{\text{Te}}_3$ films, analyzing microwave transmission across various conditions. We identify interactions with charge puddles as a primary source, providing insights critical for developing improved QAH-based technologies.

The Lorentz reciprocity is a fundamental property in electromagnetism and well known to break down due to an external magnetic field. With a fictitious or imaginary vector potential, however, its behavior is largely unknown. Here we show that in systems with an imaginary vector potential and displaying the non-Hermitian skin effect, the Lorentz reciprocity is broken but still governed by a rigorous mathematical relation, which we term non-Hermitian gauged reciprocity. When mimicking an imaginary vector potential using just linear integrated photonic elements, however, the conditions that lead to the Lorentz reciprocity are still satisfied and hence the latter cannot be broken. Nevertheless, we show that the non-Hermitian gauged reciprocity can still be observed with a proper choice of inputs and outputs, alongside the Lorentz reciprocity. In addition, we also reveal another equal-amplitude response in the same system, which we attribute to a non-Hermitian gauged symmetry. Furthermore, we show that light propagation is not impinged by the non-Hermitian topological funnel effect, highlighting an underappreciated difference between coherently driven and nondriven systems. These findings are confirmed using a tight-binding model and full-wave simulations of coupled optical microring resonators, providing a valuable extension of the Lorentz reciprocity in the non-Hermitian domain.

Describing open quantum systems in terms of effective non-Hermitian Hamiltonians gives rise to nonunitary time evolution. In this paper we study the impact of nonunitary dynamics on the emergent hydrodynamics in quantum systems with a global conservation law. To this end we demonstrate how linear-response correlation functions can be generalized and interpreted in the case of non-Hermitian systems. Moreover we show that dynamical quantum typicality provides an efficient numerical approach to evaluate such correlation functions, even though the nonunitary dynamics leads to subtleties that are absent in the Hermitian case. As a point of reference for our analysis, we consider the Hermitian spin-$1/2$ XXZ chain, whose high-temperature transport properties have been characterized extensively in recent years. Here we explore the resulting hydrodynamics for different non-Hermitian perturbations of the XXZ chain. We also discuss the role of integrability by studying the complex energy-level statistics of the non-Hermitian quantum models.

We probe the superconducting order parameter of the organic-ion-intercalated FeSe-based superconductor (tetrabutyl ammonium)${}_{0.3}\mathrm{FeSe}$ $\left[{\left(\mathrm{TBA}\right)}_{0.3}\mathrm{FeSe}\right]$ using muon-spin relaxation/rotation $\left(\mu \mathrm{SR}\right)$. Zero-field $\mu \mathrm{SR}$ measurements show only a weak temperature dependence with no evidence for magnetic ordering or broken time-reversal symmetry in the superconducting state. The temperature dependence of the superfluid density is deduced from transverse-field $\mu \mathrm{SR}$ measurements with fields applied both parallel and perpendicular to the $c$ axis, and can be well described by a nodeless two-gap $s+s$ model. These properties are reminiscent of those of $\left({\mathrm{Li}}_{1-x}{\mathrm{Fe}}_x\right){\mathrm{OHFe}}_{1-y}\mathrm{Se}$, which also has a comparably enhanced $T_c$, suggesting that such a gap structure is a common feature of quasi-two-dimensional intercalated FeSe-based superconductors.

We present SIESTA-BdG, an implementation of the simultaneous solution of the Bogoliubov-de Gennes (BdG) and density functional theory (DFT) problem in SIESTA, a first-principles method and code for material simulations which uses pseudopotentials and a localized basis set. This unified approach describes both conventional and unconventional superconducting states, and enables a description of inhomogeneous superconductors and heterostructures. We demonstrate the validity, accuracy, and efficiency of SIESTA-BdG by computing physically relevant quantities (superconducting charge density, band structure, superconducting gap features, density of states) for conventional singlet (Nb, Pb) and unconventional (FeSe) superconductors. We find excellent agreement with experiments and results obtained within the KKR-BdG computational framework. SIESTA-BdG forms the basis for modeling quantum transport in superconducting devices and including—in an approximate fashion—the superconducting DFT potential of Oliveira, Gross, and Kohn.

A defect density which quantifies the deviation from the spin ground state characterizes non-equilibrium dynamics during phase transitions. The widely recognized Kibble-Zurek scaling predicts how the defect density evolves during phase transitions. However, it can be perturbed by a noise, leading to the anti-Kibble-Zurek scaling. In this research, we analytically investigate the effect of Gaussian white noise on the transition probabilities of the Landau-Zener model. We apply this analysis to the one-dimensional transverse field Ising model and obtain an analytical approximate solution of the defect density. Our analysis reveals that when the introduced noise is small, the model follows the previously known anti-Kibble-Zurek scaling. Conversely, when the noise increases, the scaling can be obtained by using the adiabatic approximation. This result indicates that deriving the anti-Kibble-Zurek scaling does not require solving differential equations, instead, it can be achieved simply by applying the adiabatic approximation. Furthermore, we identify the parameter that minimizes the defect density based on the new scaling, which allows us to verify how effective the already known scaling of the optimized parameter is.

Artificial spin ices (ASIs) arranged in square formations have been explored from the perspective of reconfigurable magnonics. A new frontier in ASIs is their three-dimensional (3D) extension. The analytical and numerical study of such geometries is difficult due to the additional degrees of freedom. Here, we numerically explore the ferromagnetic resonance of the simplest 3D modification of a square ASI: an out-of-plane rotation of the nanomagnets. We consider cases in which the vertex gap can be either kept constant or varying with the tilt angle. We study both remanent and vortex configurations using a semianalytical dynamic approach and micromagnetic simulations. We find that both methods capture the expected qualitative frequency dependence on tilt angle based on the static stray field coupling. However, we also find important limitations for both approaches that depend on the particularities of the shape-dependent demagnetization field. These results showcase advantages and limitations of both methods in their use of predicting and understanding the resonant magnetization dynamics of 3D ASI.

A general method for calculating magnetic susceptibility $\chi$ in dielectrics within a single choice of magnetic gauge for the whole crystal is presented. On the basis of the method, accounting for all contributions to the Van Vleck paramagnetism and Langevin (Larmore) diamagnetism, a full-scale ab initio calculation of $\chi$ in diamond is performed. Unfamiliar contributions to $\chi$ includes a Van Vleck contribution from the interstitial region and an offset contribution from the muffin-tin (MT) sphere, appearing due to the change of the MT-sphere magnetic moment when the sphere is displaced from the origin. Although the Langevin diamagnetism explicitly depends on the choice of the origin, its sum with the Van Vleck term remains invariant, which is demonstrated on the basis of the gauge invariance of the magnetic vector potential. The derived expressions have been applied to ab initio calculations of magnetic susceptibility of the crystalline diamond within the linear augmented plane-wave method (LAPW). With the diamond unit cell having the inversion symmetry, the magnetic (Van Vleck) calculations require the irreducible part of the Brillouin zone accounting for half of the whole zone, i.e., 24 times larger than that in the absence of magnetic field. Investigating possible anisotropy of $\chi$, we calculate it for 74 different directions of $H$ (belonging to Lebedev surface grid points) and demonstrate that the actual value of $\chi$ remain isotropic. The obtained volume magnetic susceptibility in diamond lies in the range $-16.27-16.72$ (with the Langevin contribution $-39.22-39.94$ and the Van Vleck contribution $-22.94-23.22$), in units ${10}^{-7}$, which compares well with the experimental data and other calculations.

Antiferromagnetic (AFM) skyrmions, which are resistant to both the skyrmion Hall effect and external magnetic perturbations, are expected to be promising candidates for next-generation spintronics devices. Despite being observed in bulk materials and synthetic AFM layered systems, the existence of intrinsic AFM skyrmions within single magnetic layers, which offer potential advantages for spintronic device fabrication, has remained elusive. In this work, taking the monolayer $\mathrm{CrSi}{(\mathrm{Te},\mathrm{Se})}_3$ as a representative system, we demonstrate the emergence of intrinsic AFM skyrmions in two-dimensional Janus magnets. It is found that under moderate compressive strain, the interplay between considerable Dyzaloshinskii-Moriya interaction and the strain-induced AFM Heisenberg exchange interaction in monolayer $\mathrm{CrSi}{(\mathrm{Te},\mathrm{Se})}_3$ would give rise to the emergence of intrinsic AFM skyrmions assembled from AFM spin spirals. Moreover, the application of an external magnetic field could trigger the emergence of AFM merons as well as a canted AFM state. Our findings propose a feasible approach for achieving intrinsic AFM skyrmions in realistic systems, which paves the way for developments in AFM topological spintronics devices.

We report a microscopic mechanism for stabilization of biskyrmions in two dimensions by investigating a minimal model of classical spins on a triangular lattice with nearest-neighbor ferromagnetic Heisenberg exchange and static chiral interaction on each triangular plaquette. Our results establish that the chiral magnetic interaction results in biskyrmion states above a critical value, and its strength affects the size of the biskyrmions forming. We further explore the effects of thermal fluctuations on the biskyrmion states.

In this work, we analyze the macroscopic observables in the $1+1\mathrm{D}$ gapped phases with Abelian onsite symmetries and show that the spacetime observables for each gapped phase form a clear structure that can be mathematically described by enriched fusion categories, which uncovers the behavior of nonlocal excitations that were blurry in traditional Landau paradigm. These categorical descriptions not only generate the known classification results for symmetry preserving and breaking phases, but also unifies lattice dualities in a broader picture. After analyzing the general lattice model together with their boundaries, we give explicit examples including nontrivial SPT phase, where nontrivial boundaries can be given directly through our classification. Using enriched categorical descriptions, the lattice dualities and their gapped phases are unified under a holographic duality between an 2d. topological order with gapped 1d boundaries and $1+1\mathrm{D}$ gapped quantum liquids with a categorical symmetry, which shed light on a unified definition of all quantum phases.

We establish a universal relation between the energy gap and the static dielectric constant for all insulating states. This relation yields an upper bound on the energy gap, which only depends on the electron density and electronic dielectric constant. We identify two types of energy gaps associated with transverse and longitudinal excitations at long wavelengths, which correspond to the optical gap and the plasmon energy, respectively. Their upper bounds are set by the dielectric constant and its inverse respectively. The transverse gap bound is calculated for a wide range of materials and compared with the measured optical gap. A remarkable case is cubic boron nitride, in which the direct gap reaches $72\%$ of the bound. Our results are derived from the Kramers-Kronig relation and the $f$-sum rule and therefore rest on general physical principles.

Nodal line semimetals, a class of topological quantum materials, exhibit a variety of novel phenomena due to their properties, such as bands touching on a one-dimensional line or a ring in the Brillouin zone and drumheadlike surface states. In addition, these semimetals are protected by the combined space-inversion and time-reversal ($\mathcal{PT}$) symmetries. In this study, we investigate the longitudinal dc conductivity of the Dirac nodal line semimetals for the broken $\mathcal{PT}$-symmetric system by the mass term. Here, using the quantum kinetic technique, we find the intrinsic (field-driven) and extrinsic (scattering-driven) contributions to the total dc conductivity due to interband effects. Interestingly, the resulting intrinsic conductivity is the Fermi-sea contribution, while the extrinsic stems from the Fermi-surface contribution. We show that at low chemical potential, the extrinsic part contributes more and dominates over the traditional Drude intraband term, while at the high chemical potential, the intrinsic conductivity contributes. Furthermore, the total dc response due to interband effects saturates at high chemical potential and its strength decreases with increasing mass value. Our findings suggest that the extrinsic contributions are rich enough to understand the overall feature of the response for the three-dimensional system.

It is shown that the stroboscopic time evolution under a Floquet unitary, in any spatial dimension, and of any Hermitian operator, can be mapped to an operator Krylov space, which is identical to that generated by the edge operator of the noninteracting Floquet transverse-field Ising model (TFIM) in one-spatial dimension, and with inhomogeneous Ising and transverse field couplings. The latter has four topological phases reflected by the absence (topologically trivial) or presence (topologically nontrivial) of edge modes at 0 and/or $\pi$ quasienergies. It is shown that the Floquet dynamics share certain universal features characterized by how the Krylov parameters vary in the topological phase diagram of the Floquet TFIM with homogeneous couplings. These results are highlighted through examples, all chosen for numerical convenience to be in one spatial dimension: nonintegrable Floquet spin $1/2$ chains and Floquet $Z_3$ clock model where the latter hosts period-tripled edge modes.

Topological materials have attracted significant interest in the field of energy conversion due to their superior carrier mobility and unique topological surface states (TSSs). Despite this, the link between their topological properties and catalytic performance has not been comprehensively understood. In our study, we employ ${\mathrm{ZrTe}}_5$, a material known for its topological versatility, as a benchmark catalyst, focusing on catalytic reactions to uncover the influence of TSSs on catalysis. Contrary to the prevalent belief that TSSs are pivotal for enhanced catalytic performance, our findings reveal that spin-orbit coupling (SOC) is the actual driving force behind the observed variations in adsorption energy $\left(\mathrm{\Delta }{E}_{\text{ad}}\right)$, not the TSSs themselves. This insight applies across various topological phases, from strong topological insulators to Dirac semimetals and weak topological insulators. Furthermore, our investigation into the effects of strain, doping, and defects suggests that the role of SOC in modulating $\mathrm{\Delta }{E}_{\text{ad}}$ is minor compared to these factors. Our findings challenge the conventional idea that TSSs are what make topological materials great catalysts, suggesting a need to reevaluate the role of topology in catalysis. By uncovering that the catalytic properties of topological materials do not directly correlate with their topological states, our study paves the way for a better understanding of topological catalysis, encouraging a shift in focus towards the underlying mechanisms that drive their catalytic behaviors.

We investigated the surface stress at an Al(111) electrode surface under a finite bias voltage using first-principles density functional theory combined with the effective screening medium (ESM) method. The surface stress depends quadratically on the bias voltage, whose profile has a maximum value at a finite voltage and a curvature corresponding to the capacitance obtained from the relationship between the excess charge and the electrode voltage. These features are consistent with the results of the thermodynamics at the electrode surface and previous experiments. The results of the layer-resolved local stress show that the bias dependence of the local stress correlates with the excess charge distribution from the outermost layer to the inner layer; the local stresses at the outermost and inner layers show parabolic and linear voltage dependences, respectively. Thus, the capacitance term of the macroscopic stress mainly originates from the outermost layer, and the contribution of the inner-layer stress is understood by the strain derivative of the excess charge. The stress analysis method with ESM is significant for modeling and understanding the surface stress at the electrode surface under a bias voltage.

Using first principle calculations we examine properties of (Cd,V)Te, (Cd,Cr)Te, (Hg,V)Te, and (Hg,Cr)Te relevant to the quantum anomalous Hall effect (QAHE), such as the position of V- and Cr-derived energy levels and the exchange interactions between magnetic ions. We consider CdTe and HgTe, containing 12.5% of cation-substitutional V or Cr ions in comparison to the well-known case of (Cd,Mn)Te and (Hg,Mn)Te, and examine their suitability for fabrication of ferromagnetic barriers or ferromagnetic topological quantum wells, respectively. To account for the strong correlation of transition metal $d$ electrons we employ hybrid functionals with different mixing parameters $a_{\text{HSE}}$ focusing on $a_{\text{HSE}}=0.32$, which better reproduces the experimental band gaps in HgTe and ${\mathrm{Hg}}_{0.875}{\mathrm{Mn}}_{0.125}\mathrm{Te}$. We find that Cr, like Mn, acts as an isoelectronic dopant but V can be an in-gap donor in CdTe and a resonant donor in HgTe, similar to the case of Fe in HgSe. From a magnetic point of view, the Cr-doped HgTe is ferromagnetic within the general gradient approximation but becomes AFM within hybrid functionals. However, (Hg,V)Te is a ferromagnet within both exchange-correlation functionals in a stark contrast to (Hg,Mn)Te for which robust antiferromagnetic coupling is found theoretically and experimentally. Furthermore, we establish that the Jahn-Teller effect is relevant for the magnetism in the case of Cr-doping. Considering lower defect concentrations in HgTe-based quantum wells compared to (Bi,${\mathrm{Sb})}_3{\mathrm{Te}}_2$ layers, our results imply that HgTe quantum wells or (Cd,Hg)Te barriers containing either V or Cr show advantages over (Bi,Sb,Cr,${\mathrm{V})}_3{\mathrm{Te}}_2$-based QAHE systems but whether (i) ferromagnetic coupling will dominate in the Cr case and (ii) V will not introduce too many electrons to the quantum well is to be checked experimentally.