We present a systematic study of scalar potential induced topological transition in massive Dirac fermions. We show how a distribution of scalar potential can manipulate the signature of the gap or the mass, as well as the dispersion leading to a band inversion. This is mediated by the Klein tunneling as well as inverse Klein tunneling, which makes it inherently different from the mechanism leading to topological Anderson insulator. In one dimension it can lead to the formation of edge localization. In two dimensions this can give rise to the quantized Hall effect. Unlike conventional Hall effects, this is induced by a scalar interaction and is intrinsic in nature. Therefore, we call it a scalar Hall effect. This can facilitate direct manipulation of topological invariants, e.g., the Chern number, as well as the manipulation of the edge states locally in a trivial insulator and thus opens new possibilities for tuning physical observables which originate from the nontrivial topology.

We explore the robustness of the correlation matrix Hamiltonian reconstruction technique with respect to the choice of operator basis, studying the effects of bases that are undercomplete and overcomplete—too few or too many operators, respectively. An approximation scheme for reconstruction using an undercomplete basis is proposed and tested numerically on select models. We discuss the confounding effects of conserved quantities and symmetries on reconstruction attempts. We apply these considerations to a variety of one-dimensional systems at zero and nonzero temperature.

The interaction between light and nontrivial energy band topology allows for the precise manipulation of topological quantum states, which has attracted intensive interest in condensed-matter physics. In this work, using first-principles calculations, we studied the topological transition of ferromagnetic (FM) ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ upon irradiation with circularly polarized light (CPL). We revealed that the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ can be driven from an FM insulator to a Weyl semimetal with a minimum number of Weyl points, i.e., two Weyl points (WPs) in systems without time-reversal symmetry. More importantly, in FM ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ with an out-of-plane easy magnetization axis, we found that the band dispersion of the WP evolves from type-II to type-III and finally to type-I when the light intensity increases. Moreover, we show that the profile of the characteristic Fermi arc of the Weyl semimetal phase is sensitive to changes in light intensity, which enables efficient manipulation of the Fermi arc length of FM ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ in experiments. In addition, for FM ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ with an in-plane easy magnetization axis, the system becomes a type-I Weyl semimetal under CPL irradiation. With controllable band dispersion, the length of the Fermi arc, and a minimum number of WPs, our results indicate that CPL-irradiated FM ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ is an ideal platform for the study of novel transport phenomena in Weyl semimetals with distinct band dispersion.

This work focuses on unraveling electron paramagnetic resonance (EPR) and electrically detected magnetic resonance (EDMR) properties of $n$-type $6H$ silicon carbide (SiC) single crystals with high concentrations of uncompensated nitrogen (N) donors, which is essential for fundamental understanding of spin-related phenomena, developing spin-based devices, optimizing materials and devices, and advancing research in quantum information and spintronics. Utilizing low-temperature multifrequency EPR spectroscopy (9.4–395.12 GHz), we identified two intense signals labeled as S line and S1 line in the $6H$-SiC crystals with $N_{\mathrm{D}}–N_{\mathrm{A}}\approx 8\times {10}^{18}$ and $4\times {10}^{19}\mathrm{c}{\mathrm{m}}^{-3}$. In addition, in $6H$-SiC crystals with $N_{\mathrm{D}}–N_{\mathrm{A}}\approx 8\times {10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$, a low-intensity triplet from N donors substituting the quasicubic “k2” nonequivalent position (${\mathrm{N}}_{\mathrm{k}2}$) was observed. The S line $[g_{\perp }=2.0029\left(2\right),g_{\parallel }=2.0038\left(2\right)]$ was assigned to the exchange interaction of conduction electrons and ${\mathrm{N}}_{\mathrm{k}2}$, while the S1 line $[g_{\perp }=2.0030\left(2\right),g_{\parallel }=2.0040\left(2\right)]$ is caused by the exchange spin coupling of localized N donors at the “k1” and “k2” positions. The S1 line was observed in high-frequency EDMR spectra of $6H$-SiC with $N_{\mathrm{D}}–N_{\mathrm{A}}\approx 8\times {10}^{18}\mathrm{c}{\mathrm{m}}^{-3}$, and its emergence was explained by an enhancement of the hopping conductivity due to the EPR-induced temperature increase mechanism. No EDMR spectra were found to occur in the $6H$-SiC crystals with $N_{\mathrm{D}}–N_{\mathrm{A}}\approx 4\times {10}^{19}\mathrm{c}{\mathrm{m}}^{-3}$, which is close to the critical donor concentration value for a semiconductor-metal transition. Thus it can be concluded that this N donor concentration is too high for the appearance of spin-dependent scattering and too low for the emergence of EPR-induced hopping mechanisms in $6H$-SiC.

A tomographic study of near-field radiative heat exchanges between a mesoscopic object and a substrate immersed in a thermal bath is carried out within the theoretical framework of fluctuational electrodynamics. By using the discrete-dipole-approximation method, we compute the power density distribution for radiative exchanges and highlight the major role played by many-body interactions in these transfers. Additionally, we emphasize the close relationship between power distribution and eigenmodes within the solid paving the way to applications for hot-spot targeting at deep subwavelength scale by shape optimization.

First-principles calculations are performed to investigate the electro-optic (EO) and elasto-optic effects of the three-dimensional (bulk) and two-dimensional (monolayer) ferroelectric ${\mathrm{NbOI}}_2$. Remarkably large linear EO and elasto-optic coefficients are discovered in both systems, when under stress-free conditions. We further found that the EO responses of bulk and monolayer ${\mathrm{NbOI}}_2$ can be further enhanced with epitaxial strain, because of a strain-driven ferroelectric-to-paraelectric transition that originates from the softening of some polar optical modes. Our findings thus point out that ${\mathrm{NbOI}}_2$, as well as other niobium oxide dihalides, are highly promising for paving the way for potentially efficient nonlinear optical device applications.

Few-magnon bound states in quantum spin chains have been long studied and attracted much recent attention. For a higher-spin ferromagnetic XXZ chain with single-ion anisotropy, several features regarding the evolution of the low-lying two-magnon bound states with varying wave number were observed in the literature. However, most of these observations are only qualitatively understood due to the lack of analytical tools. By combining a set of exact two-magnon Bloch states and a plane-wave ansatz, we achieve a complete solution of the two-magnon problem in such a system. We identify parameter regions that support different types of two-magnon bound states, with the boundaries defined by algebraic equations. We discover a narrow region in which two single-ion bound states coexist. We show that the phase diagrams for distinct wave numbers are similar to each other, which enables us to map the evolution of the bound states to the rectilinear movement of a representative point for given parameters in a rescaled phase diagram. This dynamic picture provides quantitative interpretations of the observed features.

Recently, a single two-dimensional gapless Dirac cone has been experimentally observed on the surface of a semimagnetic topological insulator, providing a platform to study the physics of a single Dirac fermion. Here, we focus on Landau levels (LLs) in the presence of Anderson disorder. We find that the particle-hole (PH) asymmetric term is essential for determining the evolution of LLs with magnetic flux and disorder. With particle-hole symmetry (PHS), the zeroth LL $E_0$ is pinned at the charge-neutrality point and independent of magnetic field and weak disorder. However, with PHS broken, $E_0$ either ascends or descends depending on the sign of the PH asymmetric term. Furthermore, neighboring LLs $E_{n\ne 0}$ adhere to the antilevitation scenario for a vanishing or small PH asymmetric term. In contrast, for a sufficiently large PH asymmetric term, LLs above and below $E_0$ exhibit different behaviors. We also propose a theoretical method to understand these evolutionary behaviors of disordered LLs based on self-consistent Born approximation. Finally, we find that a rare-region-like effect occurs for a small disorder concentration, leading to rich scenarios. In particular, the zeroth LL $E_0$ becomes dependent on magnetic flux, and its dependence on disorder strength becomes nonmonotonic. Our findings offer valuable insights for understanding disordered LLs of Dirac fermions and provide guidance for experiments involving topological insulators in strong magnetic fields.

Local non-Hermitian (NH) quantum systems generically exhibit breakdown of Lieb-Robinson (LR) bounds, motivating study of whether new locality measures might shed light not seen by existing measures. In this paper we discuss extensions of the connected correlation function (CC) as measures of locality and information spreading in both Hermitian and NH systems. We find that in Hermitian systems, $\delta \rho =\rho -{\rho }_A\otimes {\rho }_B$ can be written as a linear combination of CCs, allowing placement of an LR bound on ${\parallel \delta \rho \parallel }_2$, which we show generically extends to an LR bound on mutual information. Additionally, we extend the CC to NH systems in a form that recovers locality, and use the metric formalism to derive a modified CC which recovers not just locality but even LR bounds in local $PT$-Symmetric systems. We find that even with these CCs, the bound on ${\parallel \delta \rho \parallel }_2$ breaks down in certain NH cases, which can be used to place a necessary condition on which local NH Hamiltonians are capable of nonlocal entanglement generation. Numerical simulations are provided by means of exact diagonalization for the NH Transverse-Field Ising Model, demonstrating both breakdown and recovery of LR bounds.

In this study, we explore the manganese borides (Mn-B) system, chiefly on its complex magnetic properties that are of extensive academic interest and of significant potential for applications in magnetism. We employed an approach by using a machine-learning trained, physically constrained neural network functional to reevaluate the Mn-B system comprehensively. This offers insights into several contentious aspects of the system from an enthalpy perspective, including the spin frustration in $\mathrm{M}{\mathrm{n}}_2\mathrm{B}$, the ground state of $\mathrm{Mn}{\mathrm{B}}_2$, and the ongoing debates about the synthesis and various phases of MnB and $\mathrm{Mn}{\mathrm{B}}_4$. Additionally, we establish a nearly linear relationship between the bonding strength and measured hardness in borides, which enhances the understanding of their mechanical properties with our proposed descriptor of bonding strength. Spin dynamics predictions highlight both discrepancies and consistencies related to the itinerant characteristics of magnetic moments, primarily driven by a high density of states of the magnetic atoms at the Fermi level ($E_{\mathrm{F}}$). This suggests that traditional local-moment models may be inadequate for describing these itinerant magnetic systems. This work provides insight for understanding the bonding properties and magnetism of magnetic intermetallic compounds.

Understanding the transport behavior of quantum many-body systems constitutes an important physical endeavor, both experimentally and theoretically. While a reliable classification into normal and anomalous dynamics is known to be notoriously difficult for a given microscopic model, even the seemingly simpler evaluation of transport coefficients in diffusive systems continues to be a hard task in practice. This fact has motivated the development and application of various sophisticated methods and is also the main issue of this paper. We particularly take a barely used strategy, which is based on the recursion method, and demonstrate that this strategy allows for accurate calculation of diffusion constants for different paradigmatic examples, including magnetization transport in nonintegrable spin-$1/2$ chains and ladders as well as energy transport in the mixed-field Ising model in one dimension.

We study dissipationless spin transport induced by a charge supercurrent in a monolayer van der Waals superconductor under the applied magnetic field and in a bilayer superconductor/ferromagnet (S/F) heterostructure with no external field. It is shown that in both cases a combined action of the Ising-type spin-orbit coupling and the Zeeman field results in the appearance of nonunitary superconducting triplet correlations with nonzero average Cooper pair spin, which carry spin current in the presence of a condensate motion. Properties of this dissipationless spin current are investigated. In particular, it is shown that it manifests a rectification effect. In addition, in S/F heterostructures the amplitude and the sign of the spin current are controlled by gating.

We study the interplay between intrinsic topological order and superconductivity in a two-component Haldane bilayer, where the two layers are coupled by an attractive force. We obtain the phase diagram of the model with exact diagonalization in finite size, and develop arguments to assess the stability of the observed phases in the thermodynamic limit. Our main result is that a finite critical attraction strength is needed to pair fermions forming a fractional topological order. This behavior can be harnessed to create clean interfaces between a fractional topological insulator and a superconductor by gating, wherein non-Abelian parafermionic modes are trapped. We discuss realization of such interfaces in the bulk of double bilayers of transition metal dichalcogenides by inhomogenous electrostatic gating, which should mitigate the spurious effects of disorder and crystalline defects present on physical edges.

High-symmetric homobilayer transition metal dichalcogenides (TMDs) are important members of the bilayer (BL) van der Waals material family. Here we present a systematic study of the electronic band structure in low-energy regime in homo-BL TMD structures by using the standard $k·p$ method. Six types of BL TMD stacking configurations, which satisfy the $C_3$ symmetry are considered and they are ${\mathrm{H}}_{\mathrm{M}}^{\mathrm{M}}, {\mathrm{H}}_{\mathrm{X}}^{\mathrm{M}}, {\mathrm{H}}_{\mathrm{X}}^{\mathrm{X}}, {\mathrm{R}}_{\mathrm{M}}^{\mathrm{M}}, {\mathrm{R}}_{\mathrm{X}}^{\mathrm{M}}$, and ${\mathrm{R}}_{\mathrm{M}}^{\mathrm{X}}$. The intrinsic spin-orbit coupling (SOC) in the conduction and valence bands and the phase of interlayer hopping matrix elements are included in our investigation. Taking BL ${\mathrm{MoS}}_2$ as an example, we examine the electronic energy spectra, the electron density of states, and the Fermi energies in these BL structures. We find that the electron energy dispersions in high-symmetric BL TMDs are not parabolic-like, where the band parameters (such as the energy gap, the effective electron band mass and the fourth-order correction coefficient in different subbands) depend markedly on the stacking configurations. Interestingly, the spin splitting in $\mathrm{H}$-stacked BL TMDs is suppressed because of center-inversion symmetry and time-reversal symmetry. Importantly, the phase of the interlayer hopping matrix element affects significantly the electronic properties of ${\mathrm{H}}_{\mathrm{X}}^{\mathrm{X}}$ and ${\mathrm{R}}_{\mathrm{M}}^{\mathrm{M}}$ stacked BL TMDs. The methodology and the results presented in this study can foster further exploration of the basic physical properties of BL TMDs for potential applications in electronics and optoelectronics.

Electronic transport through nanostructures can be suppressed by coherent population trapping, in which quantum coherence leads to a dark state that decouples from the drain electrode. Finite transport, then, relies on decoherence of the dark state. An alternative scenario for reduced transport is weak coupling of a state, referred to as a blocking state, to the drain. This raises the question of whether and how these two scenarios can be distinguished in the transport features. For the example of electron transport through a carbon nanotube, we analyze the full counting statistics in terms of Lee-Yang zeros and factorial cumulants. This allows us to identify regimes in which the distinction between dark and blocking state is possible and regimes in which this is not the case.

We put forward an approach to manipulate and enantioselect chiral microspheres using vortex beams that encode topological charges. Vortex beams with different topological charges transfer angular momentum to chiral particles with opposite handedness in a different way. This process also depends on the incident polarization, in a rich interplay that ultimately leads to enantioselective optical forces acting on single chiral particles with selected, arbitrary sizes. Besides this scheme also depends on the order of the topological charge, which can also be controlled experimentally. The resulting enantioselective optical forces are up to two orders of magnitude larger than the existing chiral resolution methods based on optical forces, further demonstrating the unique functionalities and applicability of the method.

We study the $\mathrm{O}{\left(N\right)}^{*}$ transitions that occur in the 3D ${\mathbb{Z}}_2$-gauge $N$-vector model and the analogous ${\mathrm{Ising}}^{*}$ transitions occurring in the 3D ${\mathbb{Z}}_2$-gauge Higgs model, corresponding to the ${\mathbb{Z}}_2$-gauge $N$-vector model with $N=1$. At these transitions, gauge-invariant correlations behave as in the usual $N$-vector (Ising for $N=1$) model. Instead, the non-gauge-invariant spin correlations are trivial and therefore the spin order parameter that characterizes the spontaneous breaking of the $\mathrm{O}\left(N\right)$ symmetry in standard $N$-vector (Ising) systems is apparently absent. We define a gauge fixing procedure—we name it stochastic gauge fixing—that allows us to define a gauge-dependent vector field that orders at the transition and is therefore the appropriate order parameter for the $\mathrm{O}\left(N\right)$ symmetry breaking. To substantiate this approach, we perform numerical simulations for $N=3$ and $N=1$. A finite-size scaling analysis of the numerical data allows us to confirm the general scenario: the gauge-fixed spin correlation functions behave as the corresponding functions computed in the usual $N$-vector (Ising) model. The emergence of a critical vector order parameter in the gauge model shows the complete equivalence of the $\mathrm{O}{\left(N\right)}^{*}$ (${\mathrm{Ising}}^{*}$) and $\mathrm{O}\left(N\right)$ (Ising) universality classes.

The optimized effective potential (OEP) approach has so far mainly been used in benchmark studies and for the evaluation of band gaps. In this work, we extend the application of the OEP by determining the analytical ionic forces within the plane-wave and pseudopotential framework. It is first shown that, due to the constrained optimization inherent to the OEP approach, an extra term needs to be added to the standard Hellmann-Feynman expression for the forces, whenever nonlocal pseudopotentials are employed. Computing this term for functionals based on Hartree-Fock and the hybrid PBE0 functional yields forces with excellent numerical accuracy. Furthermore, results for equilibrium geometries and vibrational frequencies on a set of molecules and solids confirm that the local exchange OEP is able to reproduce results obtained with the nonlocal exchange potential. Our work opens up the possibility to study lattice dynamics using advanced orbital functionals for describing exchange and correlation effects.

High harmonic generation (HHG) is a striking phenomenon, which reflects the ultrafast dynamics of electrons. Recently, it has been demonstrated that HHG can be used to reconstruct not only the energy band structure but also the geometric structure characterized by the Berry curvature. Here, we numerically investigate HHG arising from electrons coupled with a topological spin texture in a spin scalar chiral state where time reversal symmetry is broken. In this system, a sign change in scalar chirality alters the sign of the Berry curvature while keeping the energy band structure unchanged, allowing us to discuss purely geometrical effects on HHG. Notably, we found that, when the optical frequency is significantly lower than the energy gap, the sign of scalar chirality largely affects the longitudinal response parallel to the optical field rather than the transverse response. Our analysis suggests that this can be attributed to interband currents induced by the recombination of electron-hole pairs whose real-space trajectories are modulated by the anomalous velocity term.