The effects of carrier-impurity correlations due to a Kondo-like spin-spin interaction in diluted magnetic semiconductors are investigated. These correlations are not only responsible for a transfer of spins between the carriers and the impurities, but also produce nonperturbative effects in the spin dynamics such as renormalization of the precession frequency of the carrier spins, which can reach values of several percent in CdMnTe quantum wells. In two-dimensional systems, the precession frequency renormalization for a single electron spin with defined wave vector shows logarithmic divergences similar to those also known from the Kondo problem in metals. For smooth electron distributions, however, the divergences disappear due to the integrability of the logarithm. A possible dephasing mechanism caused by the wave-vector dependence of the electron spin precession frequencies is found to be of minor importance compared to the spin transfer from the carrier to the impurity system. In the Markov limit of the theory, an expression for the stationary carrier-impurity correlation energy can be deduced indicating the formation of weakly correlated carrier-impurity states with binding energies in the $\mu \mathrm{eV}$ range.

Phonon boundary scattering is typically treated using the Fuchs-Sondheimer theory, which assumes that phonons are thermalized to the local temperature at the boundary. However, whether such a thermalization process actually occurs and its effect on thermal transport remains unclear. Here we examine thermal transport along thin films with both thermalizing and nonthermalizing walls by solving the spectral Boltzmann transport equation for steady state and transient transport. We find that in steady state, the thermal transport is governed by the Fuchs-Sondheimer theory and is insensitive to whether the boundaries are thermalizing or not. In contrast, under transient conditions, the thermal decay rates are significantly different for thermalizing and nonthermalizing walls. We also show that, for transient transport, the thermalizing boundary condition is unphysical due to violation of heat flux conservation at the boundaries. Our results provide insights into the boundary scattering process of thermal phonons over a range of heating length scales that are useful for interpreting thermal measurements on nanostructures.

We study stability and switching dynamics of topological dislocations forming in a nonequilibrium polariton condensate sustained by an incoherent ring-shaped optical pump. In particular, we report on an elegant method for creation of vortices with predefined angular momenta by means of a purely incoherent (off-resonant) elliptically-shaped control beam. The control beam breaks the radiale symmetry of the system and induces chirality required for a topological charge transfer with a predefined sign. Numerical analysis encloses the optimal parameters for an effective switching between states with opposite orbital angular momenta.

The construction of exponentially localized Wannier functions for a set of bands requires a choice of Bloch-like functions that span the space of the bands in question, and are smooth and periodic functions of $\mathbf{k}$ in the entire Brillouin zone. For bands with nontrivial topology, such smooth Bloch functions can only be chosen such that they do not respect the symmetries that protect the topology. This symmetry breaking is a necessary, but not sufficient condition for smoothness, and, in general, finding smooth Bloch functions for topological bands is a complicated task. We present a generic technique for finding smooth Bloch functions and constructing exponentially localized Wannier functions in the presence of nontrivial topology, given that the net Chern number of the bands in question vanishes. The technique is verified against known results in the Kane-Mele model. It is then applied to the topological insulator ${\mathrm{Bi}}_2{\mathrm{Se}}_3$, where the topological state is protected by two symmetries: time reversal and inversion. The resultant exponentially localized Wannier functions break both these symmetries. Finally, we illustrate how the calculation of the Chern-Simons orbital magnetoelectric response is facilitated by the proposed smooth gauge construction.

By making use of the generalized Landau level representation (GLLR) for the quasiparticle propagator, we study the effect of screening on the properties of the quantum Hall states with integer filling factors in graphene. The analysis is performed in the low-energy Dirac model in the mean-field approximation, in which the long-range Coulomb interaction is modified by the one-loop static screening effects in the presence of a background magnetic field. By utilizing a rather general ansatz for the propagator, in which all dynamical parameters are running functions of the Landau level index $n$, we derive a self-consistent set of the Schwinger-Dyson (gap) equations and solve them numerically. The explicit solutions demonstrate that static screening leads to a substantial suppression of the gap parameters in the quantum Hall states with a broken $\text{U}\left(4\right)$ flavor symmetry. The temperature dependence of the energy gaps is also studied. The corresponding results mimic well the temperature dependence of the activation energies measured in experiment. It is also argued that, in principle, the Landau level running of the quasiparticle dynamical parameters could be measured via optical studies of the integer quantum Hall states.

The spin Hall effect (SHE) is one of the promising phenomena to utilize a spin current as spintronics devices, and the theoretical understanding of its microscopic mechanism is essential to know how to control its response. Although the SHE in multiorbital systems without inversion symmetry (IS) is expected to show several characteristic properties due to the cooperative roles of orbital degrees of freedom and a lack of IS, a theoretical understanding of the cooperative roles has been lacking. To clarify the cooperative roles, we study the spin Hall conductivity (SHC) derived by the linear-response theory for a $t_{2g}$-orbital tight-binding model of the $\left[001\right]$ surface or interface of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ in the presence of dilute nonmagnetic impurities. We find that the band anticrossing, arising from a combination of orbital degrees of freedom and a lack of IS, causes an increase of magnitude and a sign change of the SHC at some nonmagnetic impurity concentrations. Since a similar mechanism for controlling the magnitude and sign of the response of Hall effects works in other multiorbital systems without IS, our mechanism provides an ubiquitous method to control the magnitude and sign of the response of Hall effects in some multiorbital systems by introducing IS breaking and tuning of the nonmagnetic impurity concentration.

The density matrix renormalization group (DMRG) algorithm was originally designed to efficiently compute the zero-temperature or ground-state properties of one-dimensional strongly correlated quantum systems. The development of the algorithm at finite temperature has been a topic of much interest, because of the usefulness of thermodynamics quantities in understanding the physics of condensed matter systems, and because of the increased complexity associated with efficiently computing temperature-dependent properties. The ancilla method is a DMRG technique that enables the computation of these thermodynamic quantities. In this paper, we review the ancilla method, and improve its performance by working on reduced Hilbert spaces and using canonical approaches. We furthermore explore its applicability beyond spins systems to $t\text{−}J$ and Hubbard models.

We study how topological phases evolve in the Kane-Mele-Kondo lattice at finite temperatures and obtain the topological Doniach phase diagram. In particular, we find an intriguing crossover behavior induced by the interplay between the topological structure and electron correlations; the topological properties are restored by temperature effects. This restoration can be observed in the behavior of the bulk as well as the edge. In the bulk, we observe an increase of the spin-Hall conductivity at finite temperatures, while it is zero in the low-temperature region. At the edge, we observe gapless edge modes emerging with increasing temperature.

We fabricate ${\mathrm{La}}_x{\mathrm{Sr}}_{2-x-y}{\mathrm{Ba}}_y{\mathrm{IrO}}_{4-\delta }$ thin films by pulsed laser deposition in an effort to realize the effective carrier doping and metallization in the ${\mathrm{Sr}}_2{\mathrm{IrO}}_4$ system. We design an ideal in-plane Ir-O-Ir frame structure by utilizing tensile substrate strain and Ba substitution, as well as control La doping and oxygen deficiency. This enables us to elucidate the relation between the charge transport and the carrier density through systematic changes from an original $p$-type spin-orbit Mott insulator to a highly doped $n$-type metal.

We use scanning tunneling microscopy to study the lithium molybdenum purple bronze $\left(\mathrm{L}{\mathrm{i}}_{0.9}\mathrm{M}{\mathrm{o}}_6{\mathrm{O}}_{17}\right)$ at room temperature. Our measurements allow us to identify the single-crystal cleave plane and show that it is possible to obtain clean cleaved surfaces reflecting the crystal structure without the complications of nanoscale surface disorder. In addition to the crystal lattice, we observe a coexisting discommensurate superlattice with wave vectors $\mathit{q}=0.5{\mathit{a}}^{*}\pm 0.25{\mathit{b}}^{*}$. We propose that the origin of the superstructure is a surface reconstruction that is driven by cleaving along a crystal plane that contains in-plane $\mathrm{Mo}{\mathrm{O}}_4$ tetrahedra connected to out-of-plane $\mathrm{Mo}{\mathrm{O}}_6$ octahedra through corner-sharing oxygens. When combined with spectroscopic measurements, our studies show a promising avenue through which to study the complex physics within $\mathrm{L}{\mathrm{i}}_{0.9}\mathrm{M}{\mathrm{o}}_6{\mathrm{O}}_{17}$.

Tin (II) sulfide (SnS) is a layered mineral found in nature. In this paper, we study the two-dimensional (2D) form of this material using a combination of ab initio calculation and $\mathbf{k}·\mathbf{p}$ theory. In particular, we address the valley properties and the optical selection rules of 2D SnS. Our study reveals SnS as an extraordinary material, where there are two pairs of valleys, each placed along the two perpendicular axes, which can be selected exclusively with linearly polarized light, and can be separated using nonlocal electrical measurements.

A self-ordered nanoporous lattice formed by individual chlorine atoms on the Au(111) surface has been studied with low-temperature scanning tunneling microscopy, low-energy electron diffraction, and density functional theory calculations. We have found out that room-temperature adsorption of 0.09–0.30 monolayers of chlorine on Au(111) followed by cooling below 110 K results in the spontaneous formation of a nanoporous quasihexagonal structure with a periodicity of 25–38 Å depending on the initial chlorine coverage. The driving force of the superstructure formation is attributed to the substrate-mediated elastic interaction.

Many-body systems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipationless counterparts. The advent of numerous experimental platforms that simulate such dynamics poses an immediate challenge to systematically understand and classify these models. In particular, nontrivial many-body states emerge as steady states under nonequilibrium dynamics. While these states and their phase transitions have been studied extensively with mean-field theory, the validity of the mean-field approximation has not been systematically investigated. In this paper, we employ a field-theoretic approach based on the Keldysh formalism to study nonequilibrium phases and phase transitions in a variety of models. In all cases, a complete description via the Keldysh formalism indicates a partial or complete failure of the mean-field analysis. Furthermore, we find that an effective temperature emerges as a result of dissipation, and the universal behavior including the dynamics near the steady state is generically described by a thermodynamic universality class.

An influence of quantum effects on the equation of states and phase transitions in compressed matter is of primary interest in the physics of giant planets and in astrophysics. To gain some insight into the problem we carried out precision Raman studies of diamond isotopes ${}^{12}\text{C}, {}^{13}\text{C}$, and their mixture ${}^{12.5}\text{C}$ in the pressure range up to 73 GPa using helium as a hydrostatic pressure-transmitting medium. The ratio of Raman frequencies of ${}^{12}\text{C}$ and ${}^{13}\text{C}$ diamonds, which differs from the classical value (1.0408), was found to slightly, but nonmonotonically, change up to 60 GPa. One can propose that the quantum effects in diamonds initially are enhanced on compression to ∼30 GPa and then decrease up to the maximum experimentally measured pressure. This behavior probably unveils hidden features of covalent interaction in crystals. Examination of the isotopically mixed ${}^{12.5}\text{C}$ diamond shows that the effective mass determining the Raman frequency varies under compression from 12.38 a.u. at ambient pressure to 12.33 a.u. at pressure of 73 GPa.

We present a quantum simulation method that follows the dynamics of out-of-equilibrium many-body systems of electrons and oscillators in real time. Its cost is linear in the number of oscillators and it can probe time scales from attoseconds to hundreds of picoseconds. Contrary to Ehrenfest dynamics, it can thermalize starting from a variety of initial conditions, including electronic population inversion. While an electronic temperature can be defined in terms of a nonequilibrium entropy, a Fermi-Dirac distribution in general emerges only after thermalization. These results can be used to construct a kinetic model of electron-phonon equilibration based on the explicit quantum dynamics.

We present a complete characterization of the fluctuations and correlations of the squared overlap in the Edwards-Anderson spin-glass model in zero field. The analysis reveals that the energy-energy correlation (and thus the specific heat) has a different critical behavior than the fluctuations of the link overlap in spite of the fact that the average energy and average link overlap have the same critical properties. More precisely the link-overlap fluctuations are larger than the specific heat according to a computation at first order in the $6-\epsilon$ expansion. An unexpected outcome is that the link-overlap fluctuations have a subdominant power-law contribution characterized by an anomalous logarithmic prefactor which is absent in the specific heat. In order to compute the $\epsilon$ expansion we consider the problem of the renormalization of quadratic composite operators in a generic multicomponent cubic field theory: the results obtained have a range of applicability beyond spin-glass theory.

We study the effect of the intrinsic (Rashba or Dresselhaus) spin-orbit interaction in superconductor–nanowire–superconductor (SNS) weak links in the presence of a spin-splitting field that can result either from an intrinsic exchange field or the Zeeman effect of an applied field. We solve the full nonlinear Usadel equations numerically [The code used for calculating the results in this paper is available in https://github.com/wompo/Usadel-for-nanowires] and analyze the resulting supercurrent through the weak link and the behavior of the density of states in the center of the wire. We point out how the presence of the spin-orbit interaction gives rise to a long-range spin triplet supercurrent, which remains finite even in the limit of very large exchange fields. In particular, we show how rotating the field leads to a sequence of transitions between the 0 and $\pi$ states as a function of the angle between the exchange field and the spin-orbit field. Simultaneously, the triplet pairing leads to a zero-energy peak in the density of states. We proceed by solving the linearized Usadel equations, showing the correspondence to the solutions of the full equations and detail the emergence of the long-range supercurrent components. Our studies are relevant for ongoing investigations of supercurrent in semiconductor nanowires in the limit of several channels and in the presence of disorder.

Recently there have been several proposals of materials predicted to be nodal-ring semimetals, where zero energy excitations are characterized by a nodal ring in the momentum space. This class of materials falls between the Dirac-like semimetals and the more conventional Fermi-surface systems. As a step towards understanding this unconventional system, we explore the effects of the long-range Coulomb interaction. Due to the vanishing density of states at the Fermi level, Coulomb interaction is only partially screened and remains long-ranged. Through renormalization group and large-$N_f$ computations, we have identified a nontrivial interacting fixed point. The screened Coulomb interaction at the interacting fixed point is an irrelevant perturbation, allowing controlled perturbative evaluations of physical properties of quasiparticles. We discuss unique experimental consequences of such quasiparticles: acoustic wave propagation, anisotropic dc conductivity, and renormalized phonon dispersion as well as energy dependence of quasiparticle lifetime.