Beyond the Li-Haldane-Poilblanc conjecture, we find the entanglement Hamiltonian (EH) is actually not closely similar to the original Hamiltonian on the virtual edge. Unexpectedly, the EH has some relevant long-range interacting terms which hugely affect the physics. Without loss of generality, we study a spin-1/2 Heisenberg bilayer to obtain the entanglement information between the two layers through our newly developed quantum Monte Carlo scheme, which can simulate large-scale EH. Although the entanglement spectrum carrying the Goldstone mode seems like a Heisenberg model on a single layer, which is consistent with Li-Haldane-Poilblanc conjecture, we demonstrate that there actually exists a finite-temperature phase transition of the EH. The results violate the Mermin-Wagner theorem, which means there should be relevant long-range terms in the EH. It reveals that the Li-Haldane-Poilblanc conjecture ignores necessary corrections for the EH which may lead totally different physics.

We study the effect of coupling an electronic reservoir to a Hubbard model and to a dimer Hubbard model. This is motivated by recent experiments on the effect of illumination on the insulator-metal transition in a vanadium oxides and photoconductive cadmium sulfide heterostructure. We model the system as an electronic reservoir hybridized to the correlated system. We assume that the light intensity controls the hybridization coupling strength. We find that the light intensity acts similarly as the temperature in the weak interaction regime. This is consistent with the role played by electronic reservoirs in out-of-equilibrium systems. In contrast, qualitative differences appear at strong coupling. We show that modeling the ${\mathrm{V}}_2{\mathrm{O}}_3$ compound with a Hubbard model, our results describe qualitatively well the observed illumination-driven suppression of the insulator-metal transition. In contrast, in the DHM results fail to capture the mild suppression observed in the case of ${\mathrm{VO}}_2$. This indicates that the lattice may play an important role in this case.

Using density functional theory calculations and many-body perturbation theory, we investigate the electronic and optical properties of the inverse spinel ${\mathrm{CoFe}}_2{\mathrm{O}}_4$, a common anode material for photocatalytic water splitting. Starting with different exchange-correlation functionals, at the independent particle (IP) level we obtain a direct band gap of 1.38 eV ($\text{PBE}+U, U=4$ eV) and 1.69 eV ($\mathrm{SCAN}+ U, U=3$ eV), whereas HSE06 renders an indirect band gap of 2.02 eV. Including quasiparticle effects within $G_0{W}_0$, a larger and indirect band gap is obtained for all functionals: 1.78 eV ($\text{PBE}+U, U=4$ eV), 1.95 eV ($\mathrm{SCAN}+ U, U=3$ eV), and 2.17 eV (HSE06). Excitonic effects, taken into account by solving the Bethe-Salpeter equation (BSE), lead to a redshift of the optical band gap to 1.50 ($\mathrm{SCAN}+ U, U=3$ eV) and 1.61 eV (HSE06), in good agreement with the reported experimental values $1.50–2.0$ eV. We also explored the effect of the degree of inversion: while the band gap decreases at the IP level, including excitonic effects leads to an increase from 1.50 ($x=1$) to 1.57 ($x=0.5$), and 1.64 eV ($x=0)$. The lowest optical transitions in the visible range, identified based on the oscillator strength, are at 2.0, 3.5, and 5.0 eV for the inverse spinel, consistent with the experimental values at 2.0, 3.4, and 4.9 eV. Both $x=0.0$ and $x=0.5$ exhibit transitions below 1 eV with extremely small oscillator strengths that are absent in the inverse spinel. This corroborates previous suggestions that these transitions are related to the presence of ${\mathrm{Co}}^{2+}$ cations at the tetrahedral sites.

In recent years, helical edge states (HESs) in two-dimensional (2D) topological pseudospin photonic crystals (PhCs) have attracted more and more attention due to their pseudospin-locked unidirectional propagation of electromagnetic (EM) waves. Most of the studies are based on a kind of triangular lattice PhCs with the primitive cell containing six identical scatterers with $C_6$ symmetry. By shrinking or expanding the six-scatterer structure in the primitive cell, topological pseudospin PhCs are formed and HESs can be constructed along the zigzag interface of two PhCs with distinct topological pseudospins. In this paper, based on several 2D $C_6$ symmetric dielectric PhCs with the primitive cell containing different shapes of regular polygon prisms, we design $C_6$-like symmetric PhCs by partially replacing regular polygon prisms in the primitive cell of $C_6$ symmetric PhCs. Numerical calculations show all these different PhCs can possess similar band structures by tuning sizes of the prisms even in the $C_6$-like symmetric PhCs in which the $C_6$ symmetry is lacking. Then, by splicing these $C_6$ and $C_6$-like symmetric PhCs along their zigzag interfaces, we construct the similar HESs. Through calculating the energy propagation of these HESs, we demonstrate their same unidirectional propagation properties and the similar immunity to corners and defects along the interface. Our results indicate that the formation and the property of HESs in 2D topological pseudospin PhCs are only determined by the topological band structures and the topological pseudospins of PhCs on both sides of the interface, rather than the shapes of the scatterers in PhCs in real space. Our study provides further understanding on the formation of HESs and paves the way for control of topological edge states in practice.

Topological quasiparticles with sophisticated vectorial structures such as skyrmions play a key role in a variety of physical systems, ranging from quantum fields to magnetic materials. Wherein, optical skyrmions have attracted great attention due to their potential applications in optical information processing, transfer, and storage. In this paper, tunable plasmonic skyrmion lattices are demonstrated on graphene surfaces, where the graphene plasmons are excited using three pairs of dielectric diffractive gratings with radially polarized light beams. We have found that graphene plasmonic skyrmions with identical field distributions at different excited wavelengths can be achieved by tuning the Fermi energies without reoptimizing the grating structures, and the unit cell size of graphene plasmonic skyrmion lattices can also be actively tuned by Fermi energies at fixed excitation frequencies. Moreover, synthesized doughnut right-circularly polarized beams can also excite the plasmonic skyrmions in the axial symmetric structure with half the excitation efficiency compared to radially polarized beams. The proposed devices may find applications in optical information storage and manipulation in a chip.

We report on exceptionally long spin transport and giant spin lifetime anisotropy in the gapped surface states of three-dimensional (3D) magnetic topological insulators (MTIs). We examine the properties of these states using the three-dimensional Fu-Kane-Mele Hamiltonian model in the presence of a magnetic exchange field. The corresponding spin textures of surface states, which are well reproduced by an effective two-band model, hint at a considerable enhancement of the lifetime of out-of-plane spins compared to in-plane spins. This is confirmed by large-scale spin transport simulations for 3D MTIs with disorder. The energy dependence of the spin lifetime anisotropy arises directly from the nontrivial spin texture of the surface states, and is correlated with the onset of the quantum anomalous Hall phase. Our findings suggest different spin filtering capabilities of the gapped surface MTI states, which could be explored by nonlocal spin valve measurements.

Current proposals for topological quantum computation (TQC) based on Majorana zero modes (MZMs) have mostly been focused on coupled-wire architecture which can be challenging to implement experimentally. To explore alternative building blocks of TQC, in this paper we study the possibility of obtaining robust MZMs at the corners of triangular superconducting islands, which often appear spontaneously in epitaxial growth. We first show that a minimal three-site triangle model of spinless $p$-wave superconductor allows MZMs to appear at different pairs of vertices controlled by a staggered vector potential, which may be realized using coupled quantum dots and can already demonstrate braiding. For systems with less fine-tuned parameters, we suggest an alternative structure of a “hollow” triangle subject to uniform supercurrents or vector potentials, in which MZMs generally appear when two of the edges are in a different topological phase from the third. We also discuss the feasibility of constructing the triangles using existing candidate MZM systems and of braiding more MZMs in networks of such triangles.

Topological quantum matter exhibits transport phenomena driven by entanglement between internal degrees of freedom, as, for instance, generated by spin-orbit coupling effects. Here we report on a direct connection between the mechanism driving spin relaxation and the intertwined dynamics between spin and sublattice degrees of freedom in disordered graphene. Beyond having a direct observable consequence, such intraparticle entanglement is shown to be resilient to disorder, pointing towards a unique resource for quantum information processing.

Real-time time-dependent density functional theory (RT-TDDFT) combined with Ehrenfest molecular dynamics (EMD) is employed to study the electronic stopping power of tungsten for protons and helium ions over a wide range of ion energies. The microscopic mechanism of inner-electron excitation (including $4f$ and $5p$ electrons) in tungsten is investigated. In the low-velocity regime, our nonequilibrium simulations showed that the electronic stopping power of protons is linear with velocity, while that of helium ions deviates from the velocity proportionality due to more pronounced excitation of inner electrons. As the velocity of protons and helium ions increases, not only the contribution of $4f$-electron excitation to the electronic stopping power is verified to be significant, but also the contribution of $5p$-electron excitation is required, especially for an accurate description of the stopping maximum of tungsten. In order to provide insight into the relationship between inner-electron excitation and energy loss, the population of electron-hole pairs generated by the electron excitation is calculated. The total number of holes induced by helium ions is found to be four times as large as that induced by protons in the middle- and high-velocity regime, which is in line with the stopping ratio between helium ions and protons. The contribution of inner-electron excitation to electronic stopping power is quantitatively evaluated for both protons and helium ions. It illustrates that the inner-electron excitation is more significant for helium ions compared to protons at ion velocities below 3.0 a.u., in which the projectile ions cannot be treated as fully ionized. Given that energetic holes are crucial for the energy loss at high velocities, the energy distribution of the holes is also obtained. This distribution demonstrates that the majority of holes move towards deeper energies as the projectile velocity increases.

Atomistic spin dynamics (ASD) is a standard tool to model the magnetization dynamics of a variety of materials. The fundamental dynamical model underlying ASD is entirely classical. In this paper, we present two approaches to effectively incorporate quantum effects into ASD simulations, thus enhancing their low-temperature predictions. The first allows to simulate the magnetic behavior of a quantum spin system by solving the equations of motion of a classical spin system at an effective temperature relative to the critical temperature. This effective temperature is determined a priori from the microscopic properties of the system. The second approach is based on a semiclassical model where classical spins interact with an environment with a quantumlike power spectrum. The parameters that characterize this model can be calculated ab initio or extracted from experiments. This semiclassical model quantitatively reproduces the absolute temperature behavior of a magnetic system, thus accounting for the quantum mechanical aspects of its dynamics, even at low temperature. The methods presented here can be readily implemented in current ASD simulations with no additional complexity cost.

We propose a theory for thermal Hall transport mediated by magnons to address the impact of their damping resulting from magnon-magnon interactions in insulating magnets. This phenomenon is anticipated to be particularly significant in systems characterized by strong quantum fluctuations, exemplified by spin-1/2 systems. Employing a nonlinear flavor-wave theory, we analyze a general model for localized electron systems and develop a formulation for thermal conductivity based on a perturbation theory, utilizing bosonic Green's functions with a nonzero self-energy. We derive the expression of the thermal Hall conductivity incorporating magnon damping. To demonstrate the applicability of the obtained representation, we adopt it to two $S=1/2$ quantum spin models on a honeycomb lattice. In calculations for these systems, we make use of the self-consistent imaginary Dyson equation approach at finite temperatures for evaluating the magnon damping rate. In both systems, the thermal Hall conductivity is diminished due to the introduction of magnon damping over a wide temperature range. This effect arises due to the smearing of magnon spectra with nonzero Berry curvatures. We also discuss the relation to the damping of chiral edge modes of magnons. Our formulation can be applied to various localized electron systems as we begin with a general Hamiltonian for these systems. Our findings shed light on a new aspect of topological magnonics emergent from many-body effects and will stimulate further investigations on the impact of magnon damping on topological phenomena.

Two-dimensional systems with honeycomb lattice are known to be a paradigmatic platform to explore the various types of Hall effects, owing to that the interplay of lattice geometry, spin-orbit coupling and magnetism can give rise to very rich features in the quantum geometry of wave functions. In this work, we consider honeycomb topological antiferromagets that are effectively described by a $\mathcal{PT}$-symmetric antiferromagnetic Kane-Mele model, and explore the evolution of its nonlinear Hall response with respect to the change of lattice anisotropy, chemical potential, and the direction of the Néel vector. Due to the $\mathcal{PT}$-symmetry, the leading-order Hall effect of quantum geometric origin is the time-reversal-odd intrinsic nonlinear Hall effect, which is a second-order effect of electric fields and is independent of the scattering time. We investigate the behavior of the intrinsic nonlinear Hall conductivity tensor across topological phase transitions driven by antiferromagnetic exchange field and lattice anisotropy and find that its components do not change sign, which is different from the time-reversal-even nonlinear Hall effect of Berry curvature dipole origin. In the weakly doped regime, we find that the intrinsic nonlinear Hall effect is valley polarized. By varying the chemical potential, we find that the nonlinear Hall conductivity tensors exhibit kinks when the Fermi surface undergoes Lifshitz transitions. Furthermore, we find that the existence of spin-orbit coupling to lift the spin-rotation symmetry is decisive for the use of intrinsic nonlinear Hall effect to detect the direction of the Néel vector. Our work shows that the two-dimensional honeycomb topological antiferromagnets are an ideal class of material systems with rich properties for the study of intrinsic nonlinear Hall effect.

A key issue in the use of high-power mid-infrared (mid-IR) laser sources for a plethora of applications is the investigation of the exciting laser-driven physical phenomena taking place in materials coated with dielectric films. Here, we present a theoretical investigation of the ultrafast processes and thermal response upon excitation of two-layered complexes consisting of fused silica thin films placed on silicon substrates with ultrashort pulsed lasers in the mid-IR spectral regime. Through the development of a theoretical model, we demonstrate that the control of the underlying ultrafast phenomena and the damage threshold (DT) of the substrate are achieved via an appropriate modulation of the thickness of the ${\mathrm{SiO}}_2$ film. It is shown that a decrease of DT by up to ∼30% compared with the absence of coating is feasible, emphasizing the impact of coatings of lower refractive index than the substrate. The conditions for surface plasmon (SP) excitation on the interface between ${\mathrm{SiO}}_2$ and Si and the influence of the film thickness on the SP features are also discussed as such electromagnetic modes can initiate structuring on the interface. Our results manifested a striking impact of the presence and the coating thickness on the SP characteristics. It is shown that the SP excitation can be tailored by changing the superstrate thickness which also determines the competition of the air and the dielectric in the SP characteristics. These remarkable predictions can be employed for the development of optical coatings and components for nonlinear optics and photonics for a large range of mid-IR laser-based applications.

The ability to switch between ferromagnetic (FM) and antiferromagnetic (AFM) coupling in a material would increase the spintronic applications. To contribute, we focus on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two magnetic impurities situated on the strained and gapped topological crystalline insulating SnTe(001) surface. By considering an in-plane strain and gap, we address the potential avenues for manipulating FM and AFM couplings in diverse adjustable manners. Our approach employs calculations based on retarded Green's functions in real space. For the strain effect on the intermediate impurity separations, we find that both uniaxial and biaxial strains switch all components of the RKKY coupling including XYZ-Heisenberg and symmetric, while the existence of a gap only switches the $x$ component of the XYZ-Heisenberg coupling. By contrast, all components are switched with the strain and gap at long separations. Furthermore, we reveal that the switching process of the in-plane RKKY components can be distinctly modulated when the strain and gap coexist. To support the underlying physics of our numerical results, we provide explicit analytical expressions. These findings bear significance for magnetic data storage devices relying on topological materials.

${\mathrm{KCoO}}_2$ has been found in 1975 to exist in a unique structure with $P4/nmm$ space group featuring Co atoms in a square pyramidal coordination. The Co atoms in the plane are linked by O in a square arrangement reminiscent of the cuprates. However, its electronic structure has not been studied until now. Unlike Co atoms in ${\mathrm{LiCoO}}_2$ and ${\mathrm{NaCoO}}_2$, which are in octahedral coordination and are nonmagnetic band structure insulators, the unusual coordination of $d^6{\mathrm{Co}}^{3+}$ in ${\mathrm{KCoO}}_2$ is here shown to lead to a magnetic stabilization of an insulating structure with high magnetic moments of $4{\mu }_B$ per Co. The electronic band structure is calculated using the quasiparticle self-consistent ($\mathrm{QS})GW$ method and the basic formation of magnetic moments is explained in terms of the orbital decomposition of the bands. The optical dielectric function is calculated using the Bethe-Salpeter equation including only transitions between equal spin bands. The magnetic moments are shown to prefer an antiferromagnetic ordering along the [110] direction. Exchange interactions are calculated from the transverse spin susceptibility and a rigid spin approximation. The Néel temperature is estimated using the mean-field and Tyablikov methods and found to be between $\sim 100$ and $\sim 250\mathrm{K}$. The band structure in the AFM ordering can be related to the FM ordering by band folding effects. The optical spectra are similar in both structures and show evidence of excitonic features below the quasiparticle gap of $\sim 4\mathrm{eV}$.