We develop a density functional treatment of noninteracting Abelian anyons, which is capable, in principle, of dealing with a system of a large number of anyons in an external potential. Comparison with exact results for a few particles shows that the model captures the behavior qualitatively and semiquantitatively, especially in the vicinity of the fermionic statistics. We then study anyons with statistics parameter $1+1/n$, which are thought to condense into a superconducting state. An indication of the superconducting behavior is the mean-field result that, for uniform density systems, the ground-state energy increases under the application of an external magnetic field independent of its direction. Our density functional theory based analysis does not find that to be the case for finite systems of anyons, which can accommodate a weak external magnetic field through density transfer between the bulk and the boundary rather than through transitions across effective Landau levels, but the “Meissner repulsion” of the external magnetic field is recovered in the thermodynamic limit as the effect of the boundary becomes negligible. We also consider the quantum Hall effect of anyons, and show that its topological properties, such as the charge and statistics of the excitations and the quantized Hall conductance, arise in a self-consistent fashion.

We investigate the ground-state phase diagram of the spinful extended Haldane-Hubbard model on the honeycomb lattice using an exact-diagonalization, mean-field variational approach, and further complement it with the infinite density matrix renormalization group, applied to an infinite honeycomb cylinder. This model, governed by both on-site and nearest-neighbor interactions, can result in two types of insulators with finite local order parameters, either with spin or charge ordering. Moreover, a third one, a topologically nontrivial insulator with nonlocal order, is also manifest. We test expectations of previous analyses in spinless versions asserting that once a local order parameter is formed, the topological characteristics of the ground state, associated with a finite Chern number, are no longer present, resulting in a topologically trivial wave function. Our study confirms this overall picture, and highlights how finite-size effects may result in misleading conclusions on the coexistence of finite local order parameters and nontrivial topology in this model.

Starting from first-principles calculations on pristine stanene and using maximally localized Wannier functions (MLWFs), we analyze the different phases of the system when it is driven to a topological phase transition. The transition is achieved by a continuous parameter represented by an external electric field ${\mathcal{E}}_z$ as a generic inversion-symmetry-breaking term. We also compare the results with those of a multiorbital tight-binding (TB) model for stanene, whose hopping integrals are determined by Slater-Koster parameters. The system is in a topological (trivial) phase for ${\mathcal{E}}_z<{\mathcal{E}}_c$ (${\mathcal{E}}_z>{\mathcal{E}}_c$). We obtain that the critical field is ${\mathcal{E}}_c\simeq 0.69\mathrm{eV}/\AA$ for the more realistic MLWF compared to ${\mathcal{E}}_c\simeq 0.15\mathrm{eV}/\AA$ in the TB model. This suggests a larger stability of the topological phase of stanene when deposited on inert substrates.

We investigate the steady-state phase diagram of the dissipative spin-1/2 XYZ model on a two-dimensional triangular lattice, in which each site is coupled to a local environment. By means of cluster mean-field approximation, we find that the steady-state phases of the system are rather rich, in particular there exist various types of nonuniform antiferromagnetic phases due to the geometrical frustration. As the short-range correlations are included in the analysis, the numerical results show that the oscillatory phase disappears while the triantiferromagnetic and biantiferromagnetic phases remain to exist in the thermodynamic limit. Moreover, the existence of the spin-density-wave phase, which is missed by the single-site mean-field analysis, is also revealed by the spin-structure factor.

We present the quasiparticle band structures of prototypical oxide perovskites ${\mathrm{SrTiO}}_3$ and ${\mathrm{BaTiO}}_3$, two seemingly simple oxides for which accurate calculations of the electronic structure have been met with significant (and somewhat unexpected) challenges. Previous $G^0{W}^0$ calculations predicted a band gap ranging from 3.36 to 3.82 eV for ${\mathrm{SrTiO}}_3$, with a majority of the studies giving a band gap around 3.7 $\sim$ 3.8 eV, to be compared with the experimental value of 3.25 eV. A similar discrepancy between theory and experiment is also observed for ${\mathrm{BaTiO}}_3$. We show that the $G^0{W}^0$ approach can predict reasonably accurate band gaps of ${\mathrm{SrTiO}}_3$ and ${\mathrm{BaTiO}}_3$, provided that the calculations are carried out on top of the local density approximation (LDA) plus $U$ ($\mathrm{LDA}+U$) solutions and are fully converged. The deficiency of the LDA in describing the localized $3d$ states, although not particularly critical in this case, still results in a poor mean-field starting point for subsequent many-body perturbation calculations. $G^0{W}^0$ calculations starting from the $\mathrm{LDA}+U$ solutions, on the other hand, give significantly improved results for both systems. Our work demonstrates the accuracy and applicability of the combined $G^0{W}^0$ and $\mathrm{LDA}+U$ approach in calculating the quasiparticle band structures for materials involving localized $3d$ states, not only for systems with fully occupied $3d$ semicore states as has been shown before, but also for systems in which the $3d$ states are nominally unoccupied.

We explore the competition of doped holes and defects that leads to the loss of orbital order in vanadate perovskites. In compounds such as ${\mathrm{La}}_{1-x}{\mathrm{Ca}}_x{\mathrm{VO}}_3$ spin and orbital order result from superexchange interactions described by an extended three-orbital degenerate Hubbard-Hund model for the vanadium $t_{2g}$ electrons. Long-range Coulomb potentials of charged ${\mathrm{Ca}}^{2+}$ defects and $e\text{−}e$ interactions control the emergence of defect states inside the Mott gap. The quadrupolar components of the Coulomb fields of doped holes induce anisotropic orbital rotations of degenerate orbitals. These rotations modify the spin-orbital polaron clouds and compete with orbital rotations induced by defects. Both mechanisms lead to a mixing of orbitals, and cause the suppression of the asymmetry of kinetic energy in the $C$-type magnetic phase. We find that the gradual decline of orbital order with doping, a characteristic feature of the vanadates, however, has its origin not predominantly in the charge carriers, but in the off-diagonal couplings of orbital rotations induced by the charges of the doped ions.

In our previous work [Nozawa and Tsunetsugu, Phys. Rev. B 101, 035121 (2020)], we studied the quench dynamics in the one-dimensional Hubbard model based on the generalized hydrodynamics theory for a partitioning protocol and showed the presence of a clogging phenomenon. Clogging is a phenomenon where vanishing charge current coexists with nonzero energy current, and we found it for the initial conditions that the left half of the system is prepared to be half filling at high temperatures with the right half being empty. Clogging occurs at all the sites in the left half and lasts for a time proportional to its distance from the connection point. In this paper, we use various different initial conditions and discuss two issues. The first issue is the possibility of clogging in a stationary state. When the electron density in the right half is initially set nonzero, we found that the left half-filled part expands for various sets of parameters in the initial condition. This means that the clogging phenomenon occurs at all the sites in the long-time stationary state, and we also discuss its origin. In addition, stationary clogging is accompanied by a back current, namely, particle density current flows towards the high-density region. We also found that spin clogging occurs for some initial conditions, i.e., the vanishing spin current coexists with nonzero energy current. The second issue is the proportionality of spin and charge currents. We found two spatiotemporal regions where the current ratio is fixed to a nonzero constant. We numerically studied how the current ratio depends on various initial conditions. We also studied the ratio of charge and energy currents.

Density functional theory calculations and crystal structure predictions using the particle swarm optimization method have been combined to determine stable hydrides of lead under pressure. In contrast to other group-IVa hydrides, the stoichiometry ${\mathrm{PbH}}_6$ is the first hydride to become stable, at just under 1 Mbar. For two previously studied stoichiometries, ${\mathrm{PbH}}_4$ and ${\mathrm{PbH}}_8$, energetically more favorable phases were identified to become stable around 2 Mbar. In all structures, the hydrogenic sublattices comprise negatively charged ${{\mathrm{H}}_2}^{\delta -}$ molecules. Competitive ${\mathrm{PbH}}_4$ and ${\mathrm{PbH}}_6$ structures are layered. ${\mathrm{PbH}}_6$ features ${\mathrm{H}}_2$ molecules intercalated between hcp Pb layers, the stable phase of dense pure lead, thus offering a potentially straightforward route towards synthesis. In ${\mathrm{PbH}}_8$, the Pb lattice adapts a $\beta$-Sn structure, and hydrogen atoms form quasi-one-dimensional-chains. All structures were found to be metallic and to feature superconductivity in their respective stability range, with moderately high $T_c$ in the range 60–100 K for ${\mathrm{PbH}}_4$ and ${\mathrm{PbH}}_6$ and 161–178 K for ${\mathrm{PbH}}_8$.

We present a theoretical approach that allows for calculation of optical functions for a ${\mathrm{Cu}}_2\mathrm{O}$ quantum well (QW) with Rydberg excitons, in an external magnetic field of an arbitrary strength. Both Faraday and Voigt configurations are considered in the energetic region of $p$ excitons. We use the real density matrix approach and an effective electron-hole potential, which enable us to derive analytical expressions for the QW magneto-optical functions. For both configurations, all three field regimes—weak, intermediate, and high field—are considered and treated separately. With the help of the developed approximation method we are able to estimate the limits between the field regimes. The obtained theoretical magnetoabsorption spectra show a good agreement with available experimental data.

An exotic anomalous plasmon (AP) mode is found in strained Weyl semimetals utilizing the topological Landau Fermi liquid and chiral kinetic theories, in which quasiparticle interactions are modeled by long-range Coulomb and residual short-range interactions. The gapped collective mode is derived from the dynamical charge pumping between the bulk and the surface and behaves like $k_{\mathrm{F}}^{-1}$. The charge oscillations are accurately determined by the coupling between the induced electric field and the background pseudofields. This novel mode unidirectionally disperses along the pseudomagnetic field and manifests itself in an unusual thermal conductivity in apparent violation of the Wiedemann-Franz law. The excitation can be achieved experimentally by mechanical vibrations of the crystal lattice in the THz regime.

We propose a way to properly interpret the apparent thermal conductivity obtained for finite systems using equilibrium molecular dynamics simulations (EMD) with fixed or open boundary conditions in the transport direction. In such systems the heat current autocorrelation function develops negative values after a correlation time which is proportional to the length of the simulation cell in the transport direction. Accordingly, the running thermal conductivity develops a maximum value at the same correlation time and eventually decays to zero. By comparing EMD with nonequilibrium molecular dynamics (NEMD) simulations, we conclude that the maximum thermal conductivity from EMD in a system with domain length $2L$ is equal to the thermal conductivity from NEMD in a system with domain length $L$. This facilitates the use of nonperiodic-boundary EMD for thermal transport in finite samples in close correspondence to NEMD.

The spin-flipping effect can be induced by the Rashba spin-orbit coupling (RSOC), leading to triplet equal-spin pairs in a superconducting hybrid structure. Herein, by combining the Dirac–Bogoliubov–de Gennes equation and the Furusaki-Tsukada formalism at a finite temperature, we theoretically investigate the Josephson effect in graphene-based superconductor-ferromagnet-R-superconductor junctions, where R refers to a region with the RSOC. It is demonstrated that as a result of the RSOC, one $0\text{−}\pi$ transition can be attained by tuning the orientation of the exchange field $\vec{h}$, which is determined by its magnitude $h$ that could be periodically taken, and the periodical $0\text{−}\pi$ transitions are also caused by manipulating $h$ during a considerable scope of the orientation. More interestingly, although varying the RSOC strength $\lambda$ cannot give rise to the $0\text{−}\pi$ transition in itself, not only is it a necessary condition for the $0\text{−}\pi$ transition induced by modulating the orientation of $\vec{h}$ but also can produce the shift of the crossover point. Furthermore, two different kinds of anomalous Josephson current effect are exhibited by controlling the orientation of $\vec{h}$. Particularly, the out-of- and in-plane magnetoanisotropic Josephson currents always exist, varying monotonically with $\lambda$ while nonmonotonically with $h$. The characteristics may provide more insights into the proximity-induced RSOC and pave the way to a new class of tunable superconducting spintronic devices based on large-scale graphene.

It has been generally accepted that the spin-orbit coupling effect in noncentrosymmetric materials leads to the band splitting and nontrivial spin polarization in the momentum space. However, in some cases, zero net spin polarization in the split bands may occurs, dubbed as the band splitting with vanishing spin polarization (BSVSP) effect, protected by non-pseudo-polar point group symmetry of the wave vector in the first Brillouin zone [K. Liu et al., Nat. Commun. 10, 5144 (2019)]. In this paper, by using first-principles calculations, we show that the BSVSP effect emerges in two-dimensional (2D) nonsymmorphic $\mathrm{Ga}XY$ ($X$= Se, Te; $Y$= Cl, Br, I) family, a new class of 2D materials having in-plane ferroelectricity. Taking the GaTeCl monolayer as a representative example, we observe the BSVSP effect in the split bands along the $X\text{−}M$ line located in the proximity of the conduction band minimum. By using the $\vec{k}·\vec{p}$ Hamiltonian derived based on the symmetry analysis, we clarify that such an effect originates from the cancellation of the local spin polarization, enforced by non-pseudo-polar $C_{2v}$ point group symmetry of the wave vector along the $X\text{−}M$ line. Importantly, we find that the spin polarization can be effectively induced by applying an external out-of-plane electric field, indicating that an electrically tunable spin polarization for spintronic applications is plausible.

Quantum embedding theories can be used for obtaining quantitative descriptions of correlated materials. However, a critical challenge is solving an effective impurity model of correlated orbitals embedded in an electron bath. Many advanced impurity solvers require the approximation of a bath continuum using a finite number of bath levels, producing a highly nonconvex, ill-conditioned inverse problem. To address this drawback, this study proposes an efficient fitting algorithm for matrix-valued hybridization functions based on a data-science approach, sparse modeling, and a compact representation of Matsubara Green's functions. The efficiency of the proposed method is demonstrated by fitting random hybridization functions with large off-diagonal elements and those of a 20-orbital impurity model for a high-$T_{\mathrm{c}}$ compound, LaAsFeO, at low temperatures $\left(T\right)$. The results set quantitative goals for the future development of impurity solvers toward quantum embedding simulations of complex correlated materials.

Besides the chemical constituents, it is the lattice geometry that controls the most important material properties. In many interesting compounds, the arrangement of elements leads to pronounced anisotropies, which reflect into a varying degree of quasi-two-dimensionality of their low-energy excitations. Here we start by classifying important families of correlated materials according to a simple measure for the tetragonal anisotropy of their ab initio electronic (band) structure. Second, we investigate the impact of a progressively larger anisotropy in driving the nonlocality of many-body effects. To this end, we tune the Hubbard model from isotropic cubic in three dimensions to the two-dimensional limit and analyze it using the dynamical vertex approximation. For sufficiently isotropic hoppings, we find the low-energy self-energy to be well separable into a static nonlocal and a dynamical local contribution. While the latter could potentially be obtained from dynamical mean-field approaches, we find the former to be nonnegligible in all cases. Further, by increasing the model's anisotropy, we quantify the degree of quasi-two-dimensionality which causes this “space-time separation” to break down. Our systematic analysis improves the general understanding of electronic correlations in anisotropic or layered materials and heterostructures and provides useful guidance for future realistic studies.

We report a study of quantum oscillations (QO) in the magnetic torque of the nodal-line Dirac semimetal $\mathrm{ZrSiS}$ in the magnetic fields up to 35 T and the temperature range from 40 K down to 2 K, enabling high resolution mapping of the Fermi surface (FS) topology in the $k_z=\pi$ (Z-R-A) plane of the first Brillouin zone (FBZ). It is found that the oscillatory part of the measured magnetic torque signal consists of low frequency (LF) contributions (frequencies up to 1000 T) and high frequency (HF) contributions (several clusters of frequencies from 7–22 kT). Increased resolution and angle-resolved measurements allow us to show that the high oscillation frequencies originate from magnetic breakdown (MB) orbits involving clusters of individual $\alpha$ hole and $\beta$ electron pockets from the diamond shaped FS in the Z-R-A plane. Analyzing the HF oscillations we unequivocally show that the QO frequency from the dog-bone shaped Fermi pocket ($\beta$ pocket) amounts $\beta =591\left(15\right)$ T. Our findings suggest that most of the frequencies in the LF part of QO can also be explained by MB orbits when intraband tunneling in the dog-bone-shaped $\beta$ electron pocket is taken into account. Our results give a new understanding of the novel properties of the FS of the nodal-line Dirac semimetal $\mathrm{ZrSiS}$ and sister compounds.

The two-dimensional layered compound $\mathrm{PdCo}{\mathrm{O}}_2$ is one of the most conductive oxides, providing an intriguing research arena opened by the long mean free path and the very high mobility of $\sim 51000\mathrm{c}{\mathrm{m}}^2/\mathrm{V}\mathrm{s}$. These properties turn $\mathrm{PdCo}{\mathrm{O}}_2$ into a candidate material for nanoscale quantum devices. By exploring universal conductance fluctuations originating in nanoscale $\mathrm{PdCo}{\mathrm{O}}_2$ Hall-bar devices, we determined the phase coherence length of electron transport in $c$-axis oriented $\mathrm{PdCo}{\mathrm{O}}_2$ thin films to equal ∼100 nm. The weak temperature dependence of the measured phase coherence length suggests that defect scattering at twin boundaries in the $\mathrm{PdCo}{\mathrm{O}}_2$ thin film governs phase breaking. These results suggest that phase coherent devices can be achieved by realizing the devices smaller than the size of twin domains, via refined microfabrication and suppression of twin boundaries.

Holes confined in semiconductor nanostructures realize qubits where the quantum-mechanical spin is strongly mixed with the quantum orbital angular momentum. The remarkable spin-orbit coupling allows for fast all electrical manipulation of such qubits. We study an idealization of a cmos device where the hole is strongly confined in one direction (thin film geometry), while it is allowed to move more extensively along a one-dimensional channel. Static electric bias and ac electrical driving are applied by metallic gates arranged along the channel. In quantum devices based on materials with a bulk inversion symmetry, such as silicon or germanium, there exist different possible spin-orbit coupling based mechanisms for qubit manipulation. One of them, the $g$-tensor magnetic resonance, relies on the dependence of the effective $g$-factors on the electrical confinement. In this configuration, the hole is driven by an ac field parallel to the static electric field and perpendicular to the channel (transverse driving). Another mechanism, which we refer to here as iso-Zeeman electric dipole spin resonance, is due to the Rashba spin-orbit coupling that leads to an effective time-dependent magnetic field experienced by the pseudospin oscillating along the quantum channel (longitudinal driving). We compare these two modes of operation, and we describe the conditions in which the magnitudes of the Rabi frequencies are the largest. Different regimes can be attained by electrical tuning where the coupling to the ac electric field is made either weak or strong. Spin-orbit coupling can also be tuned by strains, with, in particular, a transition from a mostly heavy- to a mostly light-hole ground state for in-plane tensile strains. Although large strains always reduce the Rabi frequency, they may increase the qubit lifetimes even faster, which calls for a careful optimization of strains and electric fields in the devices. We also discuss the choice of channel material and orientation. The study is relevant to the interpretation of the current experiments on the manipulation of hole qubits and as a guide to the development of quantum devices based on silicon and germanium.

A generic model of two dissimilar antenna-type resonators coupled both via near-field and far-field and embedded in active gain and/or loss medium is considered. Conditions required for hitting the superscattering regime corresponding to the threshold of lasing emission operation are established. It is shown that modulation of the medium gain and losses level within realistic parameters is an efficient approach for implementation of tunability. This two-antenna setup can serve as an inspiration for the implementation of high-contrast tunable metasurfaces.

The skin effect and topological edge states in non-Hermitian systems have been well studied, and the second-order skin effect and corner modes have also been proposed in non-Hermitian systems recently. In this paper, we construct the nested tight-binding formalism to research the second-order corner modes analytically, which is a direct description of the generic non-Hermitian tight-binding model without other assumptions. Within this formalism, we obtain the exact solutions of second-order topological zero-energy corner modes for the non-Hermitian four-band model. We validate the nested tight-binding formalism in the hybrid skin-topological corner modes for the four-band model and a non-Hermitian two-dimensional (2D) extrinsic model. In addition, we exactly illustrate the corner modes induced by second-order skin effect for a simplest 2D non-Hermitian model by the nested tight-binding formalism.