We investigate electron transport through an antidot embedded in a narrow strip of a two-dimensional topological insulator. We focus on the most generic and experimentally relevant case with broken axial spin symmetry. Spin-nonconservation allows additional scattering processes, which change the transport properties profoundly. We start from an analytical model for noninteracting transport, which we also compare with a numerical tight-binding simulation. We then extend this model by including Coulomb repulsion on the antidot, and we study the transport in the Coulomb-blockade limit. We investigate sequential tunneling and cotunneling regimes, and we find that the current-voltage characteristic allows a spectroscopic measurement of the edge-state spin textures.

We study the four-terminal junction of spinless Luttinger liquid wires, which describes either a corner junction of two helical edge states of topological insulators or the tunneling from the spinful wire into the helical edge state. We use the fermionic representation and the scattering state formalism, in order to compute the renormalization group (RG) equations for the linear response conductances. We establish our approach by considering a junction between two possibly nonequivalent helical edge states and find an agreement with the earlier analysis of this situation. Tunneling from the tip of the spinful wire to the edge state is further analyzed which requires some modification of our formalism. In the latter case we demonstrate (i) the existence of both fixed lines and conventional fixed points of RG equations, and (ii) certain proportionality relations holding for conductances during renormalization. The scaling exponents and phase portraits are obtained in all cases.

We present Raman spectra of misfit layer $({\mathrm{PbS})}_{1.14}{\mathrm{NbS}}_2$ nanotubes and lead intercalated ${\mathrm{NbS}}_2$ nanotubes. They represent interesting model systems to investigate the nature of interlayer interaction in layered materials. A direct correlation to the Raman modes of the parent $2H\text{−}{\mathrm{NbS}}_2$ compound exists, but some modes are seen drastically upshifted in frequency in the misfit layer and intercalated compound while others remain almost unchanged. On the basis of the Raman spectroscopic investigations and with the help of supporting calculations we examine different interlayer bonding mechanisms and contribute to the discussion as to why these frequency shifts occur.

We investigate the $\mathrm{SU}\left(N\right)$ Hubbard model for the multicomponent fermionic optical lattice system, combining dynamical mean-field theory with the continuous-time quantum Monte Carlo method. We obtain the finite-temperature phase diagrams with $N\le 6$ and find that low-temperature properties depend on the parity of the components. The magnetically ordered state competes with the correlated metallic state in the system with an even number of components $(N\ge 4)$, yielding the first-order phase transition. It is also clarified that in the odd-component system, the ordered state is realized at relatively lower temperatures and the critical temperature is constant in the strong coupling limit.

Zeeman splitting of one-dimensional hole subbands is investigated in quantum point contacts fabricated on a (311)-oriented GaAs-AlGaAs heterostructure. Transport measurements can determine the magnitude of the $g$ factor, but cannot usually determine the sign. Here we use a combination of tilted fields and a unique off-diagonal element in the hole $g$ tensor to directly detect the sign of $g^{*}$. We are able to tune not only the magnitude, but also the sign of the $g$ factor by electrical means, which is of interest for spintronics applications. Furthermore, we show theoretically that the resulting behavior of $g^{*}$ can be explained by the momentum dependence of the spin-orbit interaction.

We investigate theoretically the phase coherence of electron transport in edge states of the integer quantum Hall effect at filling factor $\nu =2$, in the presence of disorder and inter edge state Coulomb interaction. Within a Fokker-Planck approach, we calculate analytically the visibility of the Aharonov-Bohm oscillations of the current through an electronic Mach-Zehnder interferometer. In agreement with recent experiments, we find that the visibility is independent of the energy of the current-carrying electrons injected high above the Fermi sea. Instead, it is the amount of disorder at the edge that sets the phase space available for inter edge state energy exchange and thereby controls the visibility suppression.

The search for metallic boron allotropes has attracted great attention in the past decades and recent theoretical works predict the existence of metallicity in monolayer boron. Here, we synthesize the ${\beta }_{12}$-sheet monolayer boron on a Ag(111) surface and confirm the presence of metallic boron-derived bands using angle-resolved photoemission spectroscopy. The Fermi surface is composed of one electron pocket at the $\overline{S}$ point and a pair of hole pockets near the $\overline{X}$ point, which is supported by the first-principles calculations. The metallic boron allotrope in ${\beta }_{12}$ sheet opens the way to novel physics and chemistry in material science.

The surfaces of transition-metal oxides with the perovskite structure are fertile grounds for the discovery of novel electronic and magnetic phenomena. In this article, we combine scanning transmission electron microscopy (STEM) with density functional theory (DFT) calculations to obtain the electronic and magnetic properties of the (001) surface of a ${\left(\mathrm{LaFe}{\mathrm{O}}_3\right)}_8/{\left(\mathrm{SrFe}{\mathrm{O}}_3\right)}_1$ superlattice film capped with four layers of $\mathrm{LaFe}{\mathrm{O}}_3$. Simultaneously acquired STEM images and electron-energy-loss spectra reveal the surface structure and a reduction in the oxidation state of iron from $\mathrm{F}{\mathrm{e}}^{3+}$ in the bulk to $\mathrm{F}{\mathrm{e}}^{2+}$ at the surface, extending over several atomic layers, which signals the presence of oxygen vacancies. The DFT calculations confirm the reduction in terms of oxygen vacancies and further demonstrate the stabilization of an exotic phase in which the surface layer is half metallic and ferromagnetic, while the bulk remains antiferromagnetic and insulating. Based on the calculations, we predict that the surface magnetism and conductivity can be controlled by tuning the partial pressure of oxygen.

The cohesive energy, equilibrium lattice constant, and bulk modulus of Au, Ag, and Cu noble metals are computed by different van der Waals (vdW)–corrected density functional theory (DFT) methods, including vdW-DF, vdW-DF2, vdW-DF-cx, rVV10, and PBE-D. Two specifically designed methods are also developed in order to effectively include dynamical screening effects: the DFT/vdW-WF2p method, based on the generation of maximally localized Wannier functions, and the RPAp scheme (in two variants), based on a single-oscillator model of the localized electron response. Comparison with results obtained without explicit inclusion of van der Waals effects, such as with the local density approximation (LDA), PBE, PBEsol, or the hybrid PBE0 functional, elucidates the importance of a suitable description of screened van der Waals interactions even in the case of strong metal bonding. Many-body effects are also quantitatively evaluated within the RPAp approach.

We analyze the properties of a non-Abelian spin-one chiral spin liquid state proposed by Greiter and Thomale [Phys. Rev. Lett. 102, 207203 (2009)] using Monte Carlo. In this state the bosonic $\nu =1$ Moore-Read Pfaffian wave function is used to describe a gas of bosonic spin flips on a square lattice with one flux quantum per plaquette. For toroidal geometries there is a three-dimensional space of these states corresponding to the topological degeneracy of the bosonic Moore-Read state on the torus. We show that spin correlations for different states in this space become indistinguishable for large system size. We also calculate the Renyi entanglement entropy for different system partitions to extract the topological entanglement entropy and provide evidence that the topological order of the lattice spin-liquid state is the same as that of the continuum Moore-Read state from which it is constructed.

We investigate theoretically the temporal behavior of a quantum dot under off-resonant optical excitation targeted at fast acoustic phonon-assisted state preparation. We demonstrate that in a preparation process driven by short laser pulses, three processes can be identified: a dressing of the states during the switch-on of the laser pulse, a subsequent phonon-induced relaxation, and an undressing at the end of the pulse. By analyzing excitation scenarios with different pulse shapes we highlight the decisive impact of an adiabatic undressing on the final state in short-pulse protocols. Furthermore, we show that in exciton-biexciton systems the laser characteristics such as the pulse detuning and the pulse length as well as the biexciton binding energy can be used to select the targeted quantum dot state.

We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic structure in the Fermi region. Significant density of electronic states (DOS) in proximity of the Fermi edge has been measured by photoelectron spectroscopy (PES) on surfaces exposed to air, corresponding to a $p$-type electric conductive regime, while upon annealing a depletion of the DOS has been achieved, resembling the diamond insulating state. The surface and subsurface electronic structure has been determined, exploiting the different probing depths of PES applied in a photon energy range between 7 and 31 eV. Ab initio density functional calculations including surface charge depletion and band-bending effects favorably compare with electronic states measured by angular-resolved photoelectron spectroscopy. Such states are organized in the energy-momentum space in a twofold structure: one, bulk-derived, band disperses in the $\mathrm{\Gamma }\text{−}X$ direction with an average hole effective mass of $(0.43\pm 0.02)m_0$, where $m_0$ is the bare electron mass; a second flatter band, with an effective mass of $(2.2\pm 0.9)m_0$, proves that a hole gas confined in the topmost layers is responsible for the conductivity of the $(2\times 1)$ hydrogen-terminated diamond $\left(100\right)$ surface.

The pseudospin dynamics of propagating exciton-polaritons in semiconductor microcavities are known to be strongly influenced by TE-TM splitting. As a vivid consequence, in the Rayleigh scattering regime, the TE-TM splitting gives rise to the optical spin Hall effect (OSHE). Much less is known about its role in the nonlinear optical regime in which four-wave mixing, for example, allows the formation of spatial patterns in the polariton density, such that hexagons and two-spot patterns are observable in the far field. Here we present a detailed analysis of spin-dependent four-wave mixing processes, by combining the (linear) physics of TE-TM splitting with spin-dependent nonlinear processes, i.e., exciton-exciton interaction and fermionic phase-space filling. Our combined theoretical and experimental study elucidates the complex physics of the four-wave mixing processes that govern polarization and orientation of off-axis modes.

We study the disordered XYZ spin chain using the recently developed spectrum bifurcation renormalization group [Y.-Z. You et al., Phys. Rev. B 93, 104205 (2016)] numerical method. With strong disorder, the phase diagram consists of three many-body localized (MBL) spin-glass phases. We argue that, with sufficiently strong disorder, these spin-glass phases are separated by marginally MBL critical lines. We examine the critical lines of this model by measuring the entanglement entropy and Edwards-Anderson spin-glass order parameter, and find that the critical lines are characterized by an effective central charge $c^{\prime }=ln2$. Our data also suggest continuously varying critical exponents along the critical lines. We also demonstrate how long-range mutual information [introduced in C.-M. Jian et al., arXiv:1508.07006] can distinguish these phases.

We introduce a theoretical approach to study the quantum-dissipative dynamics of electronic excitations in macromolecules, which enables to perform calculations in large systems and cover long-time intervals. All the parameters of the underlying microscopic Hamiltonian are obtained from ab initio electronic structure calculations, ensuring chemical detail. In the short-time regime, the theory is solvable using a diagrammatic perturbation theory, enabling analytic insight. To compute the time evolution of the density matrix at intermediate times, typically $\lesssim \text{ps}$, we develop a Monte Carlo algorithm free from any sign or phase problem, hence computationally efficient. Finally, the dynamics in the long-time and large-distance limit can be studied combining the microscopic calculations with renormalization group techniques to define a rigorous low-resolution effective theory. We benchmark our Monte Carlo algorithm against the results obtained in perturbation theory and using a semiclassical nonperturbative scheme. Then, we apply it to compute the intrachain charge mobility in a realistic conjugated polymer.

Oxygen interstitial site energies and migration barriers in 15 hexagonal close-packed (hcp) metals have been calculated with first-principles density functional theory. Multiple hcp systems show a preference for the hexahedral site over the tetrahedral site, as well as a stable crowdion site. More surprisingly, in more than half of the hcp systems, the oxygen does not choose the large octahedral interstitial as its ground state. We explain this result based on the effective valence of the metal from crystal-field splitting and the $c/a$ ratio. Diffusion constants for oxygen in all 15 hcp systems are calculated from analytically derived diffusion equations and match available experimental data.

The contact conductance of carbon nanotube (CNT) junctions is the key factor that controls the collective heat transfer through CNT networks or CNT-based materials. An improved understanding of the dependence of the intertube conductance on the contact structure and local environment is needed for predictive computational modeling or theoretical description of the effective thermal conductivity of CNT materials. To investigate the effect of local structure on the thermal conductance across CNT-CNT contact regions, nonequilibrium molecular dynamics (MD) simulations are performed for different intertube contact configurations (parallel fully or partially overlapping CNTs and CNTs crossing each other at different angles) and local structural environments characteristic of CNT network materials. The results of MD simulations predict a stronger CNT length dependence present over a broader range of lengths than has been previously reported and suggest that the effect of neighboring junctions on the conductance of CNT-CNT junctions is weak and only present when the CNTs that make up the junctions are within the range of direct van der Waals interaction with each other. A detailed analysis of the results obtained for a diverse range of intertube contact configurations reveals a nonlinear dependence of the conductance on the contact area (or number of interatomic intertube interactions) and suggests larger contributions to the conductance from areas of the contact where the density of interatomic intertube interactions is smaller. An empirical relation accounting for these observations and expressing the conductance of an arbitrary contact configuration through the total number of interatomic intertube interactions and the average number of interatomic intertube interactions per atom in the contact region is proposed. The empirical relation is found to provide a good quantitative description of the contact conductance for various CNT configurations investigated in the MD simulations and is suitable for incorporation into mesoscopic models capable of predicting the effective thermal transport properties of CNT materials.

The magnetic state of the tetragonal compound ${\mathrm{Ce}}_2{\mathrm{PdGe}}_3$, which crystallizes in the space group $P{4}_2/mmc$, a derivative of the $\alpha \text{−}{\mathrm{ThSi}}_2$ structure, has been investigated by magnetic susceptibility, heat capacity, muon spin relaxation $\left(\mu \mathrm{SR}\right)$, and neutron diffraction measurements. Heat capacity data indicate two separate magnetic phase transitions at $T_{N_1}=10.7$ K and $T_{N_2}=2.3$ K. The presence of bulk long-range magnetic order is confirmed by our $\mu \mathrm{SR}$ study below 11 K, where a drop of nearly 2/3 in the muon initial asymmetry and a sharp increase in the muon depolarization rate were observed. Neutron powder diffraction reveals that only one out of two Ce sites becomes magnetically ordered with magnetic propagation vector $\kappa =\left(0\right)$ at $T_{N_1}$, adopting an antiferromagnetic arrangement of magnetic moments ${\mu }_{{\text{Ce}}^{3+}}=1.78\left(1\right){\mu }_B$ along the $c$ axis. At $T_{N_2}$ the second Ce site orders similarly, following the same magnetic propagation vector $\kappa =\left(0\right)$, showing, however, at the same time a significant ferromagnetic component within the tetragonal basal plane. A second propagation vector, $\kappa =\left(\frac{1}{2},0,\frac{1}{2}\right)$, appears concomitantly at $T_{N_2}$.