In 2D topological insulators (TIs) based on semiconductor quantum wells such as HgTe/CdTe, hard wall spin-polarized edge states are calculated from an $8\times 8$ linear-$k$ multiband (LKMB) Hamiltonian based directly on $\mathbf{k}·\mathbf{p}$ theory, and from a $4\times 4$ BHZ Hamiltonian derived from it by the elimination of remote states using perturbation theory. Both approaches lead to similar results with standard boundary conditions obtained by integrating the eigenstate equation across an interface (SBCs). In contrast, open boundary conditions (OBCs) yield unphysical results and do not work for the LKMB Hamiltonian. Their failure is traced to a spurious solution introduced by the elimination process. In the BHZ treatment, SBCs are shown to be consistent with perturbation theory on both sides of the boundary, and a wall hybridization parameter is estimated for a vacuum using a basis of empty crystal free electron states. A Dirac point is not expected for a vacuum, but can exist when a thin passivation layer is used whose midgap energy is nearly degenerate with that of the TI. In the absence of interface band mixing (IBM), the Dirac point is then very close to midgap and virtually independent of the TI band asymmetry. IBM introduces a significant energy shift, which decreases monotonically with edge state wave vector. Using SBCs, the paradoxical extension of the BHZ edge states across the topological phase transition is also resolved.

We study the waiting time distributions of quantum chains coupled to two Lindblad baths at each end. Our focus is on free fermion chains, where we derive closed-form expressions in terms of single-particle matrices, allowing one to study arbitrarily large chain sizes. In doing so, we also derive formulas for 2-point correlation functions involving non-Hermitian propagators.

We construct the coordinate Bethe ansatz for all eigenstates of the open $\mathrm{spin}\text{−}\frac{1}{2}$ XXZ chain that fulfill the phantom roots criterion (PRC). Under the PRC, the Hilbert space splits into two invariant subspaces and there are two sets of homogeneous Bethe ansatz equations (BAE) to characterize the subspaces in each case. We propose two sets of vectors with chiral shocks to span the invariant subspaces and expand the corresponding eigenstates. All the vectors are factorized and have symmetrical and simple structures. Using several simple cases as examples, we present the core elements of our generalized coordinate Bethe ansatz method. The eigenstates are expanded in our generating set and show clear chirality and certain symmetry properties. The bulk scattering matrices, the reflection matrices on the two boundaries and the BAE are obtained, which demonstrates the agreement with other approaches. Some hypotheses are formulated for the generalization of our approach.

We construct a two-channel scattering model for the triangular network of valley Hall states in interlayer-biased minimally twisted bilayer graphene from symmetry arguments, and we investigate electronic transport in a four-terminal setup. In the absence of forward scattering, a single phenomenological parameter tunes the network between a triplet of chiral zigzag modes and pseudo-Landau levels. Moreover, the chiral zigzag modes give rise to robust Aharonov-Bohm resonances in the longitudinal conductance in the presence of a perpendicular magnetic field or an in-plane electric field. Interestingly, we find that when both a magnetic field and an in-plane electric field are applied, the resonances of different zigzag branches split depending on their propagation direction relative to the in-plane electric field. We further demonstrate that while the Hall response vanishes in the chiral zigzag regime, a finite Hall response is obtained without destroying the Aharonov-Bohm resonances in the longitudinal response by weakly coupling different zigzag branches, which also gives rise to Hofstadter physics at accessible magnetic fields.

Alloyed ${\mathrm{InAs}}_{0.2}{\mathrm{P}}_{0.8}/\mathrm{InP}$ nanowire quantum dot molecules reveal nontrivial electric-field evolution of the bright-exciton spectra; this was studied here using the atomistic theory. For a quantum dot molecule composed of two nanowire quantum dots of dissimilar sizes, the overall field dependence resembles the typical self-assembled quantum dot molecule spectra with an avoided crossing of direct and indirect excitons. However, for coupled nanowire quantum dots of identical dimensions and chemical compositions—where the bright-exciton splitting is triggered by alloy randomness—the notion of direct/indirect excitons is mostly lost, with the bright-exciton splitting field evolution varying strongly between various random realizations of nominally identical systems. Nonetheless, for several random samples, lower-higher excitonic branch mixing leads to the reduction of bright-exciton splitting below the $1\mu \mathrm{eV}$ threshold but with the restoration of pronounced optical activity away from the crossing. Thus, a simultaneous reduction of the bright-exciton splitting, without the detrimental reduction in the lower excitonic branch optical activity, makes alloyed nanowire quantum dot molecules a possible platform for applications in quantum optics and information.

Two-dimensional bismuth (Bi) layer, known as bismuthene, exhibits $Z2$ topological bulk states due to large spin-orbit coupling that inverts the bands. Using the tight-binding method, we calculate the band structure of buckled bismuthene to understand its topological and trivial phases. We determine the thermoelectric properties for some considered phases, incorporating the edge states contribution, by using the linearized Boltzmann transport equation with a constant relaxation time approximation. It is shown that the thermoelectric figure of merit, $ZT$, actually drops in undoped topological bismuthene due to the edge effects. Surprisingly, the topological edge states enhance $ZT$ at large doping with the Fermi energy near the bottom of bulk bands when bismuthene is nearly metallic.

Samarium nickelate ($\mathrm{Sm}\mathrm{Ni}{\mathrm{O}}_3$) is a representative quantum material, presenting “exotic” properties including strong correlations and metal-to-insulator transition. It was also shown that $\mathrm{Sm}\mathrm{Ni}{\mathrm{O}}_3$ presents the unusual antidoping effect, where the resistivity of the material increases with doping instead of decreasing. In this paper, we study intrinsic defects in this compound, and discuss the antidoping behavior in the presence of these defects. Our results show that the negatively charged oxygen vacancy ($V_{\text{O}}^{-2}$) can be very stable, and the extra electrons move towards the small octahedra (${\mathrm{Ni}}^{4+}$ sites), similar to the antidoping effect in the pristine material. This indicates that antidoping should still be observed even in the presence of defects.

The normal state out of which unconventional superconductivity in ${\mathrm{UTe}}_2$ emerges is studied in detail using a variety of thermodynamic and transport probes. Clear evidence for a broad Schottky-like anomaly with roughly $R\text{ln}2$ entropy around $T^{*}\approx 12$ K is observed in all measured quantities. Comparison with high magnetic field transport data allows the construction of an $H\text{−}T$ phase diagram resembling that of the ferromagnetic superconductor URhGe. The low-field electronic Grüneisen parameter of $T^{*}$ and that of the metamagnetic transition at $H_m\approx 35$ T are comparable pointing to a common origin of both phenomena. Enhanced Wilson and Korringa ratios suggest that the existence of short-range ferromagnetic fluctuations cannot be ruled out.

We report a comprehensive magnetization and magnetotransport study on a metallic-type of ${\mathrm{EuMnSb}}_2$ single crystals. A large Hall signal up to room temperature is found in our metallic ${\mathrm{EuMnSb}}_2$, which is dominated by hole carriers with very low carrier density and high mobility. Clear Shubnikov–de Haas oscillations are observed at low temperatures (T $<$ 30 K), from which a dominant tiny hole pocket with small effective mass is deduced. The interplay of carrier density and Mn and Eu moments results in complex magnetic ground states with two successive antiferromagnetic (AFM) transitions appearing at $T_{N1}=24 \mathrm{K}$ and $T_{N2}=9 \mathrm{K}$. In line with the rich magnetic phases, the transport properties, including magnetoresistance, quantum oscillation, and Berry phase, experience abrupt disturbances when crossing the magnetic phase boundaries. The Dirac state is likely quenched once the AFM orders set in, indicating a strong coupling between the AFM magnetic order and the band topology. Our results suggest that metallic-type ${\mathrm{EuMnSb}}_2$ is an ideal platform for the study of the interplay between magnetism, charge transport, and band topology.

We study the effects of Rashba splitting on two-leg ladders with weakly screened Coulomb interactions. Past research has shown that in this class of systems the two backscattering channels with the largest amplitude favor ordering of canonically conjugated collective fields which effectively renders the system gapless. Here we show that the band-dependent Rashba spin-orbit interaction breaks this symmetry of scattering channels, leading to a new fixed point with yet unexplored instabilities. Exotic properties can be found, for instance, the mixing of the magnetism with the charge-density wave. We then investigate the physical consequences of this partial spectral gap opening. We find a striking difference in signatures of order observed in single-particle (spectral-function) and two-body (susceptibilities) experimental probes. We conclude this paper by comparing theoretical and experimental results obtained on the Au-Si(553) platform. In STM measurements, we identify the lowest-lying soliton excitation as a hallmark of the gapped sine-Gordon model in an apparently metallic system. This implies the presence of partial spectral gaps opening. Furthermore, by ARPES measurements we confirm the expected temperature dependence of the outer bands backfolding. These two findings constitute the experimental evidence of the many-body physics proposed here.

We consider two particles hopping on a chain with a contact interaction between them. At strong interaction, there is a molecular bound state separated by a direct gap from a continuous band of atomic states. Introducing weak disorder in the interaction, the molecular state becomes Anderson-localized. At stronger disorder, part of the molecular band delocalizes and dissociates due to its hybridization to the atomic band. We characterize these different regimes by computing the density of states, the inverse participation ratio, the level-spacing statistics, and the survival probability of an initially localized state. The atomic band is best described as that of a rough billiard for a single particle on a square lattice that shows signatures of quantum chaos. In addition to typical “chaotic states,” we find states that are localized along only one direction. These “separatrix states” are more localized than chaotic states, and similar in this respect to scarred states, but their existence is due to the separatrix isoenergy line in the interaction-free dispersion relation, rather than to unstable periodic orbits.

We present a full derivation of the interaction Hamiltonian for holes in silicon within the six–band envelope-function scheme, which appropriately describes the valence band close to the $\mathit{\Gamma }$ point. The full structure of the single-hole eigenstates is taken into account, including the Bloch part. The scattering processes caused by the Coulomb interaction are shown to be both intraband and interband, the latter being mostly short-ranged. In the asymptotic long-range limit, the effective potential tends to the screened Coulomb potential and becomes purely intraband, as assumed in previous models. We apply our model to compute the excitation spectra of two interacting holes in prototypical silicon quantum dots, taking into account different dielectric environments. It is shown that, in the highly screened regime, short-range interactions (both intra- and interband) can be very relevant, while they lose importance when there is no screening other than the one proper of the bulk silicon crystal. In the latter case, we predict the formation of hole Wigner molecules.

An attempt to include the Pauli principle in the Monte Carlo method by also acting on the free-flight step and not only at the end of each collision is investigated. The charge transport in suspended monolayer graphene is considered as a test case. The results are compared with those obtained with the standard ensemble Monte Carlo technique and with the updated direct simulation Monte Carlo algorithm which is able to correctly handle with Pauli's principle. The physical aspects of the investigated approach are analyzed as well.

We adopt a geometric perspective on Fock space to provide two complementary insights into the eigenstates in many-body localized fermionic systems. On the one hand, individual many-body-localized eigenstates are well approximated by a Slater determinant of single-particle orbitals. On the other hand, the orbitals of different eigenstates in a given system display a varying, and generally imperfect, degree of compatibility, as we quantify by a measure based on the projectors onto the corresponding single-particle subspaces. We study this incompatibility between states of fixed and differing particle number, as well as inside and outside the many-body localized regime. This gives detailed insights into the emergence and strongly correlated nature of quasiparticlelike excitations in many-body localized systems, revealing intricate correlations between states of different particle numbers down to the level of individual realizations.

Fermi arc surface states, the manifestation of the bulk-edge correspondence in Weyl semimetals, have attracted much research interest. In contrast to the conventional Fermi loop, the disconnected Fermi arcs provide an exotic two-dimensional (2D) system for exploration of novel physical effects on the surface of Weyl semimetals. Here, we propose that visible conductance oscillation can be achieved in planar junctions fabricated on the surface of a Weyl semimetal with a pair of Fermi arcs. It is shown that Fabry-Pérot-type interference inside the 2D junction can generate conductance oscillation with its visibility strongly relying on the shape of the Fermi arcs and their orientation relative to the strip electrodes, the latter clearly revealing the anisotropy of the Fermi arcs. Moreover, we show that the visibility of the oscillating pattern can be significantly enhanced by a magnetic field perpendicular to the surface taking advantage of the bulk-surface connected Weyl orbits. Our work offers an effective way to identify Fermi arc surface states through transport measurement and predicts the surface of Weyl semimetals as a novel platform for the implementation of 2D conductance oscillations.

The inverse spin Hall effect (ISHE) has been recently demonstrated through the photoinduced inverse spin Hall effect (PISHE), where a focused laser normal to the device plane generates photocurrent that depends on the helicity of the photoexcitation. Here, we have employed a finite element method to rigorously simulate the helicity-dependent photocurrent (HDPC) under local helical photoexcitation, taking into account the complications of minority carriers, metal contact junctions, and spin relaxation. We found that the ISHE-induced electromotive force is inversely proportional to the doping level of the material, caused by the diffusion and drift current balance. Furthermore, the HDPC near the metal contact can either increase or decrease, because of the competing mechanisms of fast carrier recombination and spin relaxation at the contact. These simulation results provide insightful visualization of charge, spin, electric field, and current density distributions and deeper understanding of photoinduced ISHE.

For a large class of quantum many-body systems with U(1) symmetry, we prove a general inequality that relates the (off-diagonal) long-range order with the charge gap. For a system of bosons or fermions on a lattice or in the continuum, the inequality implies that a ground state with off-diagonal long-range order inevitably has a vanishing charge gap, and hence is characterized by nonzero charge susceptibility. For a quantum spin system, the inequality implies that a ground state within a magnetization plateau cannot have transverse long-range order.

Charge density waves (CDWs) in Weyl semimetals (WSMs) have been shown to induce an exotic axionic insulating phase in which the sliding mode (phason) of the CDW acts as a dynamical axion field, giving rise to a large positive magnetoconductance [Wang et al., Phys. Rev. B 87, 161107(R) (2013); Roy et al., Phys. Rev. B 92, 125141 (2015); J. Gooth et al., Nature (London) 575, 315 (2019)]. In this work, we predict that dynamical strain can induce a bulk orbital magnetization in time-reversal (TR)-invariant WSMs that are gapped by a CDW. We term this effect the “dynamical piezomagnetic effect” (DPME). Unlike in J. Gooth et al. [Nature (London) 575, 315 (2019)], the DPME introduced in this work occurs in a bulk-constant (i.e., static and spatially homogeneous in the bulk) CDW, and does not rely on fluctuations, such as a phason. By studying the low-energy effective theory and a minimal tight-binding (TB) model, we find that the DPME originates from an effective valley axion field that couples the electromagnetic gauge field with a strain-induced pseudogauge field. In particular, whereas the piezoelectric effects studied in previous works are characterized by 2D Berry curvature, the DPME represents the first example of a fundamentally 3D strain effect originating from the Chern-Simons 3-form. We further find that the DPME has a discontinuous change at a critical value of the phase of the CDW order parameter. We demonstrate that, when there is a jump in the DPME, the surface of the system undergoes a topological quantum phase transition (TQPT), while the bulk remains gapped. Hence, the DPME provides a bulk signature of the boundary TQPT in a TR-invariant Weyl CDW.

The two-dimensional electron gas at the interface between ${\mathrm{LaAlO}}_3$ and ${\mathrm{SrTiO}}_3$ (LAO/STO) exhibits gate-tunable superconductivity with a characteristic domelike shape of the critical temperature ($T_c$) in the phase diagram. As shown recently [Phys. Rev. B 102, 085420 (2020)], such an effect can be explained as a consequence of the extended $s\text{−}\mathrm{wave}$ symmetry of the gap within an intersite real space pairing scenario, leading to a good agreement between the experiment and theory. In this work, we turn to a detailed analysis of the influence of spin-orbit coupling on the LAO/STO phase diagram by considering separately the atomic component as well as the interorbital hopping induced by the broken inversion symmetry at the interface. In particular, we analyze the optimal carrier concentration for which the maximal $T_c$ is reached relative to the Lifshitz transition point. We find that the misalignment between the two can be significantly enhanced by the spin-orbit splitting of the bands, combined with the fact that superconductivity sets in when the Fermi level passes the anticrossing induced by the spin-orbital hybridization. In the presence of the external in-plane magnetic field, our calculations show fourfold anisotropy with the paramagnetic limit largely exceeded for $B_{\left|\right|}$ directed along the high symmetry points [01] and [01]. The obtained electron concentration dependence of $B_{c\left|\right|}$ reproduces the characteristic domelike shape reported in experiments and the estimated value of $B_{c\left|\right|}$ corresponds to that measured experimentally.