The generalized bulk-boundary correspondence predicts the existence of the chiral hinge states in three-dimensional second-order topological insulators (3DSOTIs), resulting in a quantized Hall effect in three dimensions. Chiral hinge states in Hermitian 3DSOTIs are characterized by the quantized transmission coefficients with zero fluctuations, even in the presence of disorders. Here, we show that chiral hinge transport in disordered non-Hermitian systems deviates from the paradigm of the Hermitian case. Our numerical calculations prove the robustness of hinge states of disordered non-Hermitian 3DSOTIs. The mean transmission coefficients may or may not equal the number of chiral hinge channels, depending on the Hermiticity of the chiral hinge states, while the fluctuations of transmission coefficients are always nonzero. Such fluctuations are not due to the broken chirality of hinge states but the incoherent scatterings of non-Hermitian potentials. The physics revealed here should also be true for one-dimensional chiral channels in topological materials that support chiral boundary states, such as Chern insulators, three-dimensional anomalous Hall insulators, and Weyl semimetals.

In this work, we report results of the quasiparticle self-consistent GW method within the framework of the linearized augmented plane-wave method. The impact of self-consistency on the electronic structure is investigated with the examples of nine semiconductors and insulators, namely, Ar, Si, SiC, C, BN, LiF, MgO, CaO, and GaAs. Possible reasons for discrepancies between different studies and implementations are discussed. For LiF, MgO, and CaO, we assess the charge-density redistribution upon self-consistency. For a representative set of materials, we investigate and confirm the absence of (any) starting-point dependence. The off-diagonal terms in the self-energy matrix are found to considerably impact the electronic structure. For better reproducibility and quality assessment, we describe the implementation of QSGW in the all-electron full-potential code exciting.

The phonon thermal transport properties of eight ternary intermetallic semiconductors are investigated by accounting for higher-order four-phonon scattering, phonon renormalization, and multichannel thermal transport. The commonly used lowest-order theory, which accounts only for three-phonon scattering and without phonon renormalization, fails drastically for the considered materials and underpredicts the thermal conductivity by up to a factor of two. The thermal conductivity decreases for three compounds and increases for five compounds with the application of higher-order corrections owing to a contrasting role of four-phonon scattering and phonon stiffening on the predicted thermal conductivity. Using the higher-order theory, at a temperature of 300 K, the lowest obtained thermal conductivity is 0.31 W/m K for ${\text{BiCsK}}_2$ and three other compounds (${\text{SbCsK}}_2$, ${\text{SbRbNa}}_2$, and ${\text{SbRbK}}_2$) have thermal conductivities lower than $0.5\text{W/m}\text{K}$ via the particlelike phonon transport channel. The contribution from the wavelike coherent transport channel is lower than 0.05 W/m K in all of these ultralow thermal conductivity compounds. The higher-order theory is crucial for the correct description of thermal transport physics, failing which the thermal transport is wrongly characterized as multichannel transport by the lowest-order theory.

A hybrid setup consisting of a superconductivity-proximitized quantum spin Hall insulator and a quantum anomalous Hall (QAH) insulator is proposed for chiral injection of electrons into the Majorana bound state (MBS). An unexplored region of the phase space involving the Zeeman-field-induced boost of the helical edge state is then proposed for the detection of the MBS. Two-dimensional transport simulations of our proposed setup are compared with the corresponding setup in the absence of the QAH region, when moderate potential and magnetic disorder are included. The remarkable contrast between the two results demonstrates the possibility for an unprecedented immunity from disorder-induced masking of the MBS detection in our proposed setup.

Over a decade of work has culminated in the consensus that one-dimensional systems, subject to sufficiently large disorder, fail to thermalize and possess an extensive set of local integrals of motion. In this Letter, I will provide numerical evidence for the contrary. In particular, this work studies the dynamics of disordered spin chains which are weakly coupled to a Markovian bath. Within this approach, the critical disorder for stability to quantum avalanches exceeds $W^{*}\gtrsim 20$ in the random field Heisenberg chain. In stark contrast to the Anderson insulator, the avalanche threshold drifts considerably with system size, with no evidence of saturation in the studied regime.

We report a breakthrough development allowing one to solve a broad class of polaron problems with highly nonlinear electron-phonon coupling that were considered unsolvable without uncontrolled simplifications in the past using a Monte Carlo technique formulated in the coordinate representation for both the particle and the atomic displacements. The only condition is the sign positivity of the hopping amplitude. The technique dramatically simplifies (with the corresponding efficiency gains) for models with dispersionless phonons. Our study sheds important light on the nature and universality of the most striking qualitative and quantitative effects demonstrated by the “standard” (Peierls/Su-Schrieffer-Heeger) model based on the linearized displacement-modulated hopping.

In novel ultrapure materials electrons can form a viscous fluid, which is fundamentally different in its dynamics from the electron gas in ordinary conductors with a significant density of defects. The shape of the nonstationary flow of such an electron fluid is similar to the alternating flow of blood in large-radius arteries [J. R. Womersley, J. Physiol. 127, 553 (1955)]. The rotational viscosity effect is responsible for the interconnection between the dynamics of electron spins and flow inhomogeneities. In particular, it induces the spin polarization of electrons in a curled flow via an internal spin-orbit torque acting on electron spins. Here, we show that this effect in an electron fluid placed in a magnetic field leads to a correction to the ac sample impedance, which has a resonance at the Larmor frequency of electrons. In this way, via the electrically detected spin resonance, the Womersley flow of an electron fluid can be visualized and the rotational viscosity can be measured.

It has been shown that coherent phonons can be used as a potent tool for controlling and enhancing optoelectronic and transport properties of nanostructured materials. Recent studies revealed that interaction of acoustic phonons and fast-moving carriers in semiconductor heterostructures can be accompanied by electron-phonon instabilities that cause ordinary and induced Cherenkov effects. However, the development of such instabilities is still poorly understood. Our study shows that other supersonic phenomena, beyond the Cherenkov instability, are possible for nonequilibrium charge transport in the miniband semiconductor superlattices (SLs) driven by an acoustic plane wave. Using semiclassical nonperturbative methods and elements of the bifurcation theory, we find the conditions for the onset of dynamical instabilities (bifurcations) which are caused by the emission of specific SL phonons by supersonic electrons, and their back action on the electrons. Notably, the underlying radiation mechanism is connected either to normal or anomalous Doppler effects in full accordance with the Ginzburg-Frank-Tamm theory. The appearance of induced Doppler effects is also discussed in relation to the formation of electron bunches propagating through the spatially periodic structure of the SL. When the amplitude of the acoustic wave exceeds a certain threshold, the dynamical instabilities developed in the system are manifested as drift velocity reversals, resonances in sound attenuation, and absolute negative mobility. We demonstrate that the discovered superluminal Doppler phenomena can be utilized for tunable broadband amplification and generation of GHz-THz electromagnetic waves, which creates a ground for the development of novel phononic devices.

Josephson junctions containing ferromagnetic materials exhibit interesting physics and show promise as circuit elements for superconducting logic and memory. For memory applications, the properties of the junction should be controllable by changing the magnetic configuration inside the junction. To achieve good magnetic switching properties, one should choose a soft magnetic material such as NiFe (permalloy); however, NiFe exhibits poor supercurrent transmission in Josephson junctions. In this paper, we put thin layers of Ni on either side of the NiFe and characterize the magnetic behavior and supercurrent transmission properties of the Ni/NiFe/Ni trilayers as a function of Ni and NiFe thicknesses. Using a Ni thickness of 0.4 nm, we find that the magnetic switching behavior of the trilayers is not severely degraded relative to plain NiFe, while the maximum supercurrent in the $\pi$ state of the trilayer Josephson junctions is increased by a factor of four relative to that of NiFe junctions. We speculate that the supercurrent enhancement is due to the different spin-dependent transport properties of the Cu/Ni and Cu/NiFe interfaces.

In the presence of quasiperiodic potentials, the celebrated Kitaev chain presents an intriguing phase diagram with ergodic, localized, and multifractal states. In this work, we generalize these results by studying the localization properties of the Aubry-André-Harper model in the presence of long-range hopping and superconducting pairing amplitudes. These amplitudes decay with power-law exponents $\xi$ and $\alpha$, respectively. To this end, we review and compare a toolbox of global and local characterization methods in order to investigate different types of transitions between ergodic, localized, and multifractal states. We report energy-dependent transitions from ergodic to multifractal states for pairing terms with $\alpha <1$ and energy-dependent transitions from ergodic to localized states with an intermediate multifractal region for $\alpha >1$. The size of the intermediate multifractal region depends not only on the value of the superconducting pairing term $\mathrm{\Delta }$, but also on the energy band. The transitions are not described by a mobility edge, but instead we report hybridization of bands with different types of localization properties. This leads to coexisting multifractal regimes where fractal dimensions follow different distributions.

Monolayer FeSe grown on ${\mathrm{SrTiO}}_3$ provides a playground for high-$T_c$ superconductivity. Authors of a recent study have shown the importance of stripy instability for superconductivity enhancement in $\mathrm{FeSe}\text{/}{\mathrm{SrTiO}}_3$. However, it is still under debate whether such a stripe phase is ubiquitously bound to the interfacial superconductivity. Here, we report on molecular beam epitaxy growth and a low-temperature scanning tunneling microscopy study of FeSe films on $\mathrm{BaTi}{\mathrm{O}}_3\left(001\right)$. We find that the stripe phase is more prominent in $\mathrm{FeSe}\text{/}\mathrm{BaTi}{\mathrm{O}}_3$. Long-range stripes exist in bilayer and triple-layer FeSe films at 4 K and even persist up to 77 K in the case of bilayer FeSe, with enlarged superconducting gaps upon alkali-metal deposition. The results point out an intimate correlation between the interfacial superconductivity and the stripe phase.

Starting from a realistic extended Hubbard model for a $p_{x,y}$-orbital tight-binding model on the Honeycomb lattice, we perform a thorough investigation of the possible electron instabilities in magic-angle twisted bilayer graphene near the van Hove (VH) dopings. Here we focus on the interplay between the two symmetries of the system. One is the approximate $\mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)$ symmetry which leads to the degeneracy between the intervalley spin density wave (SDW) and valley density wave (VDW) as well as that between the intervalley singlet and triplet superconductivities (SCs). The other is the $D_3$ symmetry which leads to the degeneracy among the three symmetry-related wave vectors of the density-wave (DW) orders, originating from the Fermi-surface nesting. The interplay between these two degeneracies leads to intriguing quantum states relevant to recent experiments, as revealed by our systematic random-phase-approximation based calculations followed by a succeeding mean-field energy minimization for the groundstate energy. At the $\mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)$ symmetric point, the degenerate intervalley SDW and VDW are mixed into a new state of matter dubbed as the chiral SO(4) spin-valley DW. This state simultaneously hosts three four-component vectorial spin-valley DW orders with each adopting one wave vector, and the polarization directions of the three DW orders are mutually perpendicular to one another. In the presence of a tiny intervalley exchange interaction with coefficient $J_H\to 0^{-}$ which breaks the $\mathrm{SU}\left(2\right)\times \mathrm{SU}\left(2\right)$ symmetry, a pure chiral SDW state is obtained. In the case of $J_H\to 0^{+}$, although a nematic VDW order is favored, the two SDW orders with equal amplitudes are accompanied simultaneously. This nematic $\mathrm{VDW}+\mathrm{SDW}$ state possesses a stripy distribution of the charge density, consistent with the recent STM observations. On the aspect of SC, while the triplet $p+ip$ and singlet $d+id$ topological SCs are degenerate at $J_H=0$ near the VH dopings, the former (latter) is favored for $J_H\to 0^{-}$ ($J_H\to 0^{+}$). In addition, the two asymmetric doping-dependent behaviors of the obtained pairing phase diagram are well consistent with experiments.

Compressed clathrate superhydrides have been the most promising candidates for room-temperature superconductors since the theory-oriented findings of ${\mathrm{CaH}}_6, {\mathrm{YH}}_9, {\mathrm{LaH}}_{10}$ et. al., where the hydrogen clathrate framework was believed to play a critical role in improving superconductivity. Recently, a ternary superhydride of ${\mathrm{Li}}_2{\mathrm{MgH}}_{16}$ was predicted to be a “hot” superconductor with a theoretical $T_c$ value up to 473 K at 250 GPa, although it exhibits the metastable feature under high pressure. With the aim of seeking thermodynamically stable ternary clathrate superhydrides, by exploring the high-pressure phase diagram of the $\mathrm{Li}\text{–}R\text{–}\mathrm{H} (R=\mathrm{Sc},\mathrm{Y},\text{and}\mathrm{La})$ systems at 300 GPa, we identified several thermodynamically ternary superhydrides with high-temperature superconductivity. Among these predicted stable structures, as a result of extensive simulations, clathrate structured ${\mathrm{Li}}_2{\mathrm{YH}}_{17}$ and ${\mathrm{Li}}_2{\mathrm{LaH}}_{17}$ are predicted to be high-temperature superconductors with a superconducting critical temperature ($T_c$) up to 108 and 156 K, at 200 and 160 GPa, respectively. Interestingly, a superhydride, $Immm$–${\mathrm{Li}}_2{\mathrm{ScH}}_{20}$, with mixed molecular and atomic hydrogen, is predicted to possess a high $T_c$ of 242 K at 300 GPa. The present results may stimulate the future experiment for the investigation of structural, electronic, and superconducting properties of metal-doped rare-earth superhydrides, which thus help the further design and discovery of superconducting clathrate superhydrides.

Chevrel phase materials form a family of ternary molybdenum chalcogenides with a general chemical formula $A_x{\mathrm{Mo}}_6{X}_8$ $(A=\text{metal elements},X=\text{chalcogen})$. The variety of $A$ atoms makes a large number of family members and leads to many tunable physical properties, such as the superconductivity, thermoelectricity, and the ionic conductivity. In this work, we have further found various nontrivial band topological states in these materials by using first-principle calculations. The compounds having time-reversal symmetry, such as ${\text{BaMo}}_6{\text{S}}_8, {\text{SrMo}}_6{\text{S}}_8$, and ${\text{Mo}}_6{\text{S}}_8$, are topological insulators in both of the $R\overline{3}$ and $P\overline{1}$ phases, whereas ${\text{EuMo}}_6{\text{S}}_8$ within ferromagnetic state is an axion insulator in the $R\overline{3}$ phase and a trivial one in the $P\overline{1}$ phase. This indicates that the change of $A$ ions can modify the chemical potential, lattice distortion, and magnetic orders, which offers a unique way to influence the topological states and other properties. We hope this work can stimulate further studies of Chevrel phase materials to find more intriguing phenomena, such as topological superconducting states and Majorana modes.

We report first-principles total-energy electronic-structure calculations, based on density-functional theory, that unveil detailed atomic structures of hydrogen-adsorbed step edges and their energetics of the silicon carbide (SiC) (0001) surface. The obtained adsorption energy of the hydrogen atom at each step reveals the microscopic reason for the step morphology on the Si-face SiC(0001) surfaces which are commonly inclined toward the $\langle 11\overline{2}0\rangle$ direction in epitaxial growth. The calculated hydrogen coverages at each step and also on the surface terrace clearly identify the favorable reaction sites for the epitaxial growth, such as chemical vapor deposition (CVD) in which hydrogen is ubiquitous. The obtained results provide a firm theoretical framework to discuss the atom-scale mechanism of the epitaxial growth of SiC.

The recent discovery of the quantum nonlinear Hall effect has revived the field of nonlinear transport. Here, we investigate the magnetic-field-induced nonlinear transport in time reversal symmetric Weyl semimetals. We show that the interplay of the band-geometric quantities, such as the Berry curvature, and the magnetic part of the Lorentz force can give rise to finite nonlinear Hall conductivity that is linear in the magnetic field. In addition, we show that the chiral chemical potential which represents chiral anomaly gives rise to linear magnetic-field-dependent nonlinear longitudinal conductivities along with the nonlinear Hall conductivities. Such nonlinear conductivities can manifest through nonlinear transport measurement as well as nonlinear optical phenomena like photocurrent and the second harmonic generation.

The conductance of electrostatic wire junctions in bilayer graphene, classified as trivial-trivial or trivial-topological regarding the confinement character on each junction side, is calculated. The topological side always corresponds to a kink-antikink system, as required for a proper connection with a trivial side. We report a conductance quench of the trivial-topological junction, with a conductance near quantization to $4e^2/h$, which is only half of the maximum value allowed by the Chern number of a kink-antikink system. The analysis allowed us to uncover the existence of a chiral edge mode in the trivial wire under quite general conditions. A double junction, trivial-topological-trivial, displays periodic Fano-like conductance resonances (dips or peaks) induced by the created topological loop.