We study theoretically spin current generation from band insulator$\mathsf{s}$ with PT symmetry, which is associated with Zener tunneling in strong dc electric fields. Each band in these systems is doubly degenerate with opposite spins, but spin rotational symmetry is not preserved in general. We consider the condition for spin current generation in connection with the nature of the wave function, which ultimately depends on a geometric quantity known as the shift vector. From an analysis of a two-band model, we find that the shift vector is necessary for spin current generation in PT-symmetric system$\mathsf{s}$. We also present zigzag chain models that have shift vectors, and confirm from numerical calculations that a nonzero tunneling spin current occurs in spin-degenerate systems.

The average distance $h_0$ separating two contacting bodies is a critical parameter for many problems, for example, for control of unwanted stiction in micro/nanoelectromechanical systems. Here this problem is analyzed in relation to precise determination of the dispersion forces in a difficult for measurement range of $5-30\mathrm{nm}$. The unloaded contact between two deposited rough films characterized by a relatively large number of high asperities is considered. The equilibrium distance $h_0$ can be found from the balance of attractive dispersion forces and repulsive forces acting in the spots of real contact. A simple columnar model associated with AFM images of rough surfaces is used to describe the balance. The numerical analysis, which treats the high asperities as elastoplastic semispheroids, demonstrates that the columnar model describes the contact adequately. It is shown that in contrast with the value of $h_0$ the adhesion energy between the surfaces is nearly entirely defined by the dispersion interaction, but the effects of contact interaction and plastic deformations can be neglected. This property is proposed to use for more precise determination of the equilibrium distance.

Two-dimensional Dirac semimetals have attracted a great deal of attention because of their linear energy dispersion and nontrivial Berry phase. These materials are rare because the nodal band structure is fragile against perturbations such as the spin-orbit coupling (SOC). Recently, it has been reported that nonsymmorphic crystal lattices possess symmetry-enforced Dirac-like band dispersion around certain high symmetry momenta even in the presence of SOC. Here we calculate the optical absorption spectra of the nonsymmorphic semimetals, which hosts anisotropic Dirac cones, with different Fermi velocities along the $x$ and $y$ directions. Our calculations show that the optical absorption coefficient depends strongly on the anisotropy factor and the photon polarization. By rotating the latter, one can change the absorption coefficient by more than an order of magnitude, giving rise to birefringence. When a magnetic field is applied, the absorption coefficient also depends on an internal parameter, which we term the “mixing angle” of the band structure. This parameter becomes therefore accessible to experimental investigation. We further find that an in-plane magnetic field, while leaving the system gapless, can induce a Van Hove singularity in the joint density of states: this causes a significant enhancement of the optical absorption at the frequency of the singularity for one direction of polarization but not for the orthogonal one, making the optical properties even more strongly dependent on polarization and anisotropy. These results suggest that a very pure nonsymmorphic two-dimensional Dirac semimetal can be an excellent candidate material for tunable magneto-optic devices.

Using the triangular-lattice extended Hubbard model as a test system, we compare $GW+\mathrm{EDMFT}$ results for the recently proposed self-consistency scheme with causal auxiliary fields to those obtained from the standard implementation which identifies the impurity Green's functions with the corresponding local lattice Green's functions. Both for short- and long-ranged interactions we find similar results, but the causal scheme yields slightly stronger correlation effects at half-filling. We use the two implementations of $GW+\mathrm{EDMFT}$ to compute spectral functions and dynamically screened interactions in the parameter regime relevant for $1T\text{−}{\mathrm{TaS}}_2$. These simulations allow us to clarify if the sample used in a recent photoemission study [M. Ligges et al., Phys. Rev. Lett. 120, 166401 (2018)] was half-filled or hole doped.

Quantum many-particle systems in which the kinetic energy, strong correlations, and band topology are all-important pose an interesting and topical challenge. Here we introduce and study particularly simple models where all of these elements are present. We consider interacting quantum particles in two dimensions in a strong magnetic field such that the Hilbert space is restricted to the lowest Landau level (LLL). This is the familiar quantum Hall regime with rich physics determined by particle filling and statistics. A periodic potential with a unit cell enclosing one flux quantum broadens the LLL into a Chern band with a finite bandwidth. The states obtained in the quantum Hall regime evolve into conducting states in the limit of large bandwidth. We study this evolution in detail for the specific case of bosons at filling factor $\nu =1$. In the quantum Hall regime, the ground state at this filling is a gapped quantum hall state (the “bosonic Pfaffian”), which may be viewed as descending from a (bosonic) composite Fermi liquid. At large bandwidth, the ground state is a bosonic superfluid. We show how both phases and their evolution can be described within a single theoretical framework based on a LLL composite fermion construction. Building on our previous work on the bosonic composite Fermi liquid, we show that the evolution into the superfluid can be usefully described by a noncommutative quantum field theory in a periodic potential.

The Grüneisen ratio (GR) has emerged as a superb tool for the diagnosis of quantum phase transitions; it diverges algebraically upon approaching critical points of continuous phase transitions. However, this paradigm has been challenged recently by observations of a finite GR for self-dual criticality and divergent GR at symmetry-enhanced first-order transitions. To unveil the fascinating GR further, we exemplify the idea by studying an exactly solvable quantum Ising model with Dzyaloshinskii-Moriya interaction, which harbors a ferromagnetic phase, a paramagnetic phase, and a chiral Luttinger liquid. Although the self-dual criticality of the ferromagnetic-paramagnetic transition is undermined by the Dzyaloshinskii-Moriya interaction, we find that the GR at the transition is still finite albeit with an increasing value, signifying a proximate self-dual relation. By contrast, the GR at the transition between the gapped ferromagnetic phase and the gapless Luttinger liquid diverges and changes its sign when crossing the first-order transition. This implies that the GR could also probe the first-order transition between the gapped and gapless phases.

We provide an efficient and accurate method for converting Hartree-Fock-Bogoliubov wave functions into matrix product states (MPSs). These wave functions, also known as Bogoliubov vacua, exhibit a peculiar entanglement structure that the eigenvectors of the reduced density matrix are also Bogoliubov vacua. We exploit this important feature to obtain their optimal MPS approximation and derive an explicit formula for corresponding MPS matrices. The performance of our method is benchmarked with the Kitaev chain and the Majorana-Hubbard model on the honeycomb lattice. The approach facilitates the applications of Hartree-Fock-Bogoliubov wave functions and is ideally suited for combining with the density-matrix renormalization group method.

Creating and manipulating topological states is a key goal of condensed matter physics. Periodic driving offers a powerful method to manipulate electronic states, and even to create topological states in solids. Here, we investigate the tunable Floquet states in a periodically driven higher-order nodal-line semimetal with both spatial inversion and time-reversal symmetries. We found that the Floquet Weyl semimetal states, which support both one-dimensional hinge Fermi arc and two-dimensional surface Fermi arc states, can be induced in the higher-order nodal-line semimetal by shining circularly polarized light. Moreover, we show that the location of Weyl nodes and the curvature of surface Fermi arcs can be tuned by adjusting the propagation direction and incident angle of light.

We address the possibility of atomic-scale control of the plasmon modes of graphene nanostructures. Using the time-dependent many-body approach we show that for the zigzag and armchair nanoribbons, the single carbon atom vacancy results in “on” and “off” switching of the longitudinal plasmon modes or in a change of their frequency. The effect stems from the robust underlying physical mechanism based on the strong scattering of the two-dimensional (2D) electrons on the vacancy defects in graphene lattice. Thus our findings establish a platform for optical response engineering or sensing in 2D materials.

Diamond is used extensively as a component in high-energy-density experiments, but existing equation of state (EOS) models do not capture its observed response to dynamic loading. In particular, in contrast with first-principles theoretical models of equilibrium multiphase EOS, no solid-solid phase changes have been detected, and no general-purpose EOS models match the measured ambient isotherm. We have performed density functional theory (DFT) calculations of the diamond phase to $\sim 10$ TPa, well beyond its predicted range of thermodynamic stability, and used these results as the basis of a Mie-Grüneisen EOS. We also performed DFT calculations of the elastic moduli, and calibrated an algebraic elasticity model for use in simulations. We then estimated the flow stress of diamond by comparison with the stress-density relation measured experimentally in ramp-loading experiments. The resulting constitutive model allows us to place a constraint on the Taylor-Quinney factor (the fraction of plastic work converted to heat) from the observation that diamond does not melt on ramp compression.

Probing the relaxation dynamics of glasses at temperatures far below the glass transition remains challenging owing to the extremely slow relaxation characteristic and the lack of appropriate experimental techniques. We utilized a sensitive laser reflection curvature method to probe the slow relaxation dynamics of metallic glassy (MG) films of different thicknesses at room temperature. It was found that the relaxation dynamics of MG films can be dramatically accelerated by the thickness reduction, similar to the role of temperature. We also compared the size-induced relaxation of MG films to the relaxation of MG ribbons at varying temperatures. Similar effects of size and temperature on the relaxation dynamics are revealed. We show that a MG film with a thickness of $\sim 10$ nm at room temperature has a fast relaxation dynamics equivalent to that of a bulk MG near the glass transition temperature within an observation time scale of 1 s, indicating that the liquidlike behavior in glass can be induced by size reduction. Our observation for MGs, similar to that of polymer glasses reported previously, suggests that the size-induced enhanced relaxation dynamics and glass transition is universal in glassy materials.

We consider a sublattice-symmetric free-fermion model on a one-dimensional lattice with random hopping amplitudes decaying with the distance as $|t_l|\sim l^{-\alpha }$, and address the question how far an analog of the random-singlet state (RSS) conceived originally for describing the ground state of certain random spin chains is valid for this model. For this purpose, we study the effective central charge characterizing the logarithmic divergence of the entanglement entropy (EE) and the prefactor of the distribution of distances between localization centers on the two sublattices, which must fulfill a consistency relation for a RSS. For $\alpha >1$, we find by exact diagonalization an overall logarithmic divergence of the entanglement entropy with an effective central charge varying with $\alpha$. The large-$\alpha$ limit of the effective central charge is found to be different from that of the nearest-neighbor hopping model. The consistency relation of RSS is violated for $\alpha \le 2$, while for $\alpha >2$ it is possibly valid, but this conclusion is hampered by a crossover induced by the short-range fixed point. The EE is also calculated by the strong-disorder renormalization group (SDRG) method numerically. Aside from the traditional scheme, we construct and apply a more efficient minimal SDRG scheme having a linear (nearest-neighbor) structure, which turns out to be an accurate approximation of the full SDRG scheme for not too small $\alpha$. The SDRG method is found to provide systematically lower effective central charges than exact diagonalization does, nevertheless, it becomes more and more accurate for increasing $\alpha$. Furthermore, as opposed to nearest-neighbor models, it indicates a weak dependence on the disorder distribution.

Quantum localization in 1D non-Hermitian systems, especially the search for exact single-particle mobility edges, has attracted considerable interest recently. While much progress has been made, the available methods to determine the ME in such models are still limited. In this work, we use a new method to find a new class of exact mobility edges in 1D non-Hermitian quasiperiodic models with parity-time $\left(\mathcal{PT}\right)$ symmetry. We illustrate our method by studying a specific model. We first use our method to determine the energy-dependent mobility edge as well as the spectrum for localized eigenstates in this model. We then demonstrate that the metal-insulator transition must occur simultaneously with the spontaneous $\mathcal{PT}$-symmetry breaking transition in this model. Finally, we propose an experimental protocol based on a 1D photonic lattice to distinguish the extended and localized single-particle states in our model. The results in our work can be applied to studying other non-Hermitian quasiperiodic models.

In this work, the effects of bulk Dzyaloshinskii-Moriya interactions (BDMIs) on magnetic domain walls in noncentrosymmetric chiral magnets are investigated. For static walls, their chirality is jointly determined by BMDI strength and the hard-easy ratio. When external magnetic fields or electronic currents are applied, the Walker limit is considerably enhanced by BDMIs. Domain walls can acquire high enough steady-flow velocity that they are more easily liberated from various blocking mechanisms and thus can serve as fast carriers of information. In addition, modifications of the BDMI strength and hard-easy ratio to the walls' drifting velocity far beyond Walker breakdown are presented. Our findings open possibilities for the development and optimization of future magnetic nanodevices with high performance and better environmental friendliness.

In this paper, we investigate the low temperature magnetic properties of the rare-earth garnet compound ${\mathrm{Nd}}_3{\mathrm{Ga}}_5{\mathrm{O}}_{12}$ in detail by means of magnetization, specific heat, and magnetocaloric effect measurements. The magnetic thermal properties along with the crystal field calculations reveal that the ${\mathrm{Nd}}^{3+}$ ions form into a frustrated hyper-kagome lattice with connected triangles have an Ising-like ground state with the easy axis along the local [100], [010], and [001] directions. Instead of a quantum spin liquid ground state, an antiferromagnetically ordered state is found below $T_{\mathrm{N}}=0.52\mathrm{K}$. With applying field in the [111] direction, the antiferromagnetic order is suppressed at the critical field of $B_{\mathrm{c}}=0.75\mathrm{T}$, and enhancement of the critical fluctuations with linear crossover behaviors is observed near the critical point.

A unique Kondo lattice praseodymium monoxide PrO was synthesized in the form of an epitaxial thin film. The rocksalt-type PrO thin films with a $4f^{2}5d^1$ electronic configuration showed metallic conduction with a local resistivity minimum at 7 K as a result of the Kondo effect. In contrast to the other paramagnetic praseodymium monochalcogenides, PrO showed weak ferromagnetism below 28 K, followed by a transition to a more ferromagneticlike phase around 5 K. Emergence of the weak ferromagnetism probably originated from the enhanced $4f\text{−}4f$ exchange interaction by the short Pr-Pr distance. For the ferromagneticlike phase below 5 K, magnetic hysteresis of the anomalous Hall effect was significantly larger than that of magnetization, probably due to competing magnetic ordering.

We explore proximity-induced magnetocaloric effect (MCE) on transition metal dichalcogenides, focusing on a two-dimensional (2D) ${\mathrm{MoTe}}_2$ monolayer deposited on a ferromagnetic semiconductor EuO substrate connected to a heat source. We model this heterostructure using a tight-binding model, incorporating exchange, and Rashba fields induced by proximity to EuO and including temperature through Fermi statistics and mean-field calculations. The MCE is induced on the 2D ${\mathrm{MoTe}}_2$ layer due to the EuO substrate, revealing large spin-polarized entropy changes for energies out of the band gap of the ${\mathrm{MoTe}}_2$-EuO system. By gating the chemical potential, the MCE can be tuned to produce heating for spin up and cooling for spin down across the $K$- and $K^{\prime }$-valley splitting in the valence band, whereas heats for both spins in the conduction band up to the EuO Curie temperature. The Rashba field enhances the MCE in the valence zone whereas decreasing it in the conduction bands. The exchange field-induced MCE could be useful to produce tunable spin-polarized thermal responses in magnetic proximitized 2D materials.

Different from the skyrmion driven by the Dzyaloshinskii-Moriya interaction in noncentrosymmetric materials, the skyrmionic texture in centrosymmetric magnet may possess the extra internal degrees of freedom, which greatly enrich its morphologies, imply the continuous deformation allowed by topological protection, and enable flexible tunability and potential functionality. To describe the internal degree of freedom to the full extent, the conventional integer-valued scalar vorticity is extended into a vector vorticity with continuous rotation allowed. The further simplified vorticity angle, together with helicity angle, represents the whole rotation freedom of spin space. The centrosymmetric magnet with frustration provides a perfect platform for realizing a controllable manipulation on these internal degrees of freedom, where the magnetic field can be applied to tune vorticity continuously in both crystal and isolated forms of skyrmionic texture, and the helicity can be further controlled by electric field. Moreover, the simulation reveals the distinctive dynamic effects related to the vorticity modulation, namely, a straight motion can be generated by rotating magnetic field to tune vorticity, and the vorticity can also be controlled to modulate the dynamics induced by the spin-polarized current.

We study a topological spin Hall effect where conduction electrons are scattered by Néel-type skyrmions in two-dimensional Rashba spin-orbit ferromagnets. We find the resonance structures in direct and Hall electric conductivities. The resonances strongly depend on the skyrmion size, the Rashba spin-orbit coupling vector value, and the relative direction between magnetization and Rashba vectors. The antiparallel arrangement of the Rashba spin-orbit coupling vector with respect to the magnetization determines the resonance structure and increases the direct conductivity by about two orders of magnitude. For the parallel arrangement the electric conductivities decrease by one to three orders of magnitude and the Hall conductivity changes the sign. The Rashba spin-orbit coupling also modifies electron bands depending on the ratio ${\varepsilon }_R/J$, where ${\varepsilon }_R$ is Rashba energy and $J$ is an exchange integral between conduction and localized electrons. If ${\varepsilon }_R/J\le 1$, each energy band has the single minimum while for ${\varepsilon }_R/J>1$ the lower band has the “Mexican-hat” shape with the maximum at $k=0$. We focus on the dependencies of direct and Hall electric conductivities on Fermi energy, ${\varepsilon }_F$, skyrmion sizes, and Rashba spin-orbit coupling constant values and its relative direction with the magnetization. Analyzing both types of the energy bands, in general, we find two types of resonances: at the minimum of the upper band and behaviors, we employ the scattering pattern analysis. The resonance dependencies on skyrmion sizes and Rashba, a spin-orbit coupling contestant, can be qualitatively explained in terms of the Ramsauer-Townsend scattering of the upper band electrons by the skyrmion quantum well. The resonance properties can be used in spin transistors. To discover the resonances it is necessary to know the specific range of the parameters. At some values of the parameters the electric conductivity changes by about two orders of magnitude in the narrow range of ${\varepsilon }_F$ ($<0.01$ eV). To detect the resonances it is also important to identify the relative direction of the Rashba spin-orbit coupling vector with respect to the magnetization.

We study numerically the process of vortex nucleation in the wake of a moving object in superfluids using a generalized and nonlocal Gross-Pitaevskii model. The nonlocal potential is set to reproduce the roton minimum present in the excitation spectrum of superfluid helium. By applying numerically a Newton-Raphson method we determine the bifurcation diagram for different types of nonlinearities and object sizes which allow for determining the corresponding critical velocities. In the case of a nonlocal potential, we observe that for small object sizes the critical velocity is simply determined by the Landau criterion for superfluidity, whereas for large objects there is little difference between all models studied. Finally, we study dynamically in two and three dimensions how rotons and vortices are excited in the nonlocal model of superfluid.