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Spin-orbit coupling in quasi-one-dimensional Wigner crystals ; Pedder, Christopher ; Schmidt, Thomas in Physical Review B (2017), 95(4), 045413 We study the effect of Rashba spin-orbit coupling (SOC) on the charge and spin degrees of freedom of a quasi-one-dimensional (quasi-1D) Wigner crystal. As electrons in a quasi-1D Wigner crystal can move ... [more ▼] We study the effect of Rashba spin-orbit coupling (SOC) on the charge and spin degrees of freedom of a quasi-one-dimensional (quasi-1D) Wigner crystal. As electrons in a quasi-1D Wigner crystal can move in the transverse direction, SOC cannot be gauged away in contrast to the pure 1D case. We show that for weak SOC, a partial gap in the spectrum opens at certain ratios between density of electrons and the inverse Rashba length. We present how the low-energy branch of charge degrees of freedom deviates due to SOC from its usual linear dependence at small wave vectors. In the case of strong SOC, we show that spin sector of a Wigner crystal cannot be described by an isotropic antiferromagnetic Heisenberg Hamiltonian any more, and that instead the ground state of neighboring electrons is mostly a triplet state. We present a new spin sector Hamiltonian and discuss the spectrum of Wigner crystal in this limit. [less ▲] Detailed reference viewed: 29 (3 UL)Dynamic response functions and helical gaps in interacting Rashba nanowires with and without magnetic fields Pedder, Christopher ; ; et al in Physical Review B (2016), 94(24), 245414 A partially gapped spectrum due to the application of a magnetic field is one of the main probes of Rashba spin-orbit coupling in nanowires. Such a ``helical gap'' manifests itself in the linear ... [more ▼] A partially gapped spectrum due to the application of a magnetic field is one of the main probes of Rashba spin-orbit coupling in nanowires. Such a ``helical gap'' manifests itself in the linear conductance, as well as in dynamic response functions such as the spectral function, the structure factor, or the tunnelling density of states. In this paper, we investigate theoretically the signature of the helical gap in these observables with a particular focus on the interplay between Rashba spin-orbit coupling and electron-electron interactions. We show that in a quasi-one-dimensional wire, interactions can open a helical gap even without magnetic field. We calculate the dynamic response functions using bosonization, a renormalization group analysis, and the exact form factors of the emerging sine-Gordon model. For special interaction strengths, we verify our results by refermionization. We show how the two types of helical gaps, caused by magnetic fields or interactions, can be distinguished in experiments. [less ▲] Detailed reference viewed: 20 (1 UL)Lifting the Franck-Condon blockade in driven quantum dots Haughian, Patrick ; ; et al in Physical Review. B : Condensed Matter (2016), 94 Electron-vibron coupling in quantum dots can lead to a strong suppression of the average current in the sequential tunneling regime. This effect is known as Franck-Condon blockade and can be traced back ... [more ▼] Electron-vibron coupling in quantum dots can lead to a strong suppression of the average current in the sequential tunneling regime. This effect is known as Franck-Condon blockade and can be traced back to an overlap integral between vibron states with different electron numbers which becomes exponentially small for large electron-vibron coupling strength. Here, we investigate the effect of a time-dependent drive on this phenomenon, in particular the effect of an oscillatory gate voltage acting on the electronic dot level. We employ two different approaches: perturbation theory based on nonequilibrium Keldysh Green's functions and a master equation in Born-Markov approximation. In both cases, we find that the drive can lift the blockade by exciting vibrons. As a consequence, the relative change in average current grows exponentially with the drive strength. [less ▲] Detailed reference viewed: 10 (1 UL)Helical gaps in interacting Rashba wires Schmidt, Thomas Scientific Conference (2016, September) Detailed reference viewed: 8 (1 UL)Emission of entangled Kramers pairs from a helical mesoscopic capacitor Dolcetto, Giacomo ; Schmidt, Thomas in Physical Review B (2016), 94(7), 075444 The realization of single-electron sources in integer quantum Hall systems has paved the way for exploring electronic quantum optics experiments in solid-state devices. In this work, we characterize a ... [more ▼] The realization of single-electron sources in integer quantum Hall systems has paved the way for exploring electronic quantum optics experiments in solid-state devices. In this work, we characterize a single Kramers pair emitter realized by a driven antidot embedded in a two-dimensional topological insulator, where spin-momentum locked edge states can be exploited for generating entanglement. Contrary to previous proposals, the antidot is coupled to both edges of a quantum spin Hall bar, thus enabling this mesoscopic capacitor to emit an entangled two-electron state. We study the concurrence $C$ of the emitted state and the efficiency $F$ of its emission as a function of the different spin-preserving and spin-flipping tunnel couplings of the antidot with the edges. We show that the efficiency remains very high ($Fgeq 50) even for maximally entangled states ($C=1$). We also discuss how the entanglement can be probed by means of noise measurements in a simple two-terminal setup. [less ▲] Detailed reference viewed: 23 (3 UL)Generic Helical Liquids: Theory & Applications Rod, Alexia ; Dolcetto, Giacomo ; et al Poster (2016, August 23) Detailed reference viewed: 21 (9 UL)Transport through a quantum spin Hall antidot as a spectroscopic probe of spin textures Rod, Alexia ; Dolcetto, Giacomo ; et al in Physical Review B (2016), 94 We investigate electron transport through an antidot embedded in a narrow strip of two-dimensional topological insulator. We focus on the most generic and experimentally relevant case with broken axial ... [more ▼] We investigate electron transport through an antidot embedded in a narrow strip of two-dimensional topological insulator. We focus on the most generic and experimentally relevant case with broken axial spin symmetry. Spin-non-conservation 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. [less ▲] Detailed reference viewed: 68 (10 UL)Spin textures and response functions of helical electron systems Schmidt, Thomas Scientific Conference (2016, July) Detailed reference viewed: 7 (1 UL)The topological Anderson insulator phase in the Kane-Mele model ; ; et al in Scientific Reports (2016), 6 It has been proposed that adding disorder to a topologically trivial mercury telluride/cadmium telluride (HgTe/CdTe) quantum well can induce a transition to a topologically nontrivial state. The resulting ... [more ▼] It has been proposed that adding disorder to a topologically trivial mercury telluride/cadmium telluride (HgTe/CdTe) quantum well can induce a transition to a topologically nontrivial state. The resulting state was termed topological Anderson insulator and was found in computer simulations of the Bernevig-Hughes-Zhang model. Here, we show that the topological Anderson insulator is a more universal phenomenon and also appears in the Kane-Mele model of topological insulators on a honeycomb lattice. We numerically investigate the interplay of the relevant parameters, and establish the parameter range in which the topological Anderson insulator exists. A staggered sublattice potential turns out to be a necessary condition for the transition to the topological Anderson insulator. For weak enough disorder, a calculation based on the lowest-order Born approximation reproduces quantitatively the numerical data. Our results thus considerably increase the number of candidate materials for the topological Anderson insulator phase. [less ▲] Detailed reference viewed: 58 (7 UL)The helical gap in interacting Rashba wires at low electron densities Schmidt, Thomas ; Pedder, Christopher E-print/Working paper (2016) Rashba spin-orbit coupling and a magnetic field perpendicular to the Rashba axis have been predicted to open a partial gap ("helical gap") in the energy spectrum of noninteracting or weakly interacting ... [more ▼] Rashba spin-orbit coupling and a magnetic field perpendicular to the Rashba axis have been predicted to open a partial gap ("helical gap") in the energy spectrum of noninteracting or weakly interacting one-dimensional quantum wires. By comparing kinetic energy and Coulomb energy we show that this gap opening typically occurs at low electron densities where the Coulomb energy dominates. To address this strongly correlated limit, we investigate Rashba wires using Wigner crystal theory. We find that the helical gap exists even in the limit of strong interactions but its dependence on electron density differs significantly from the weakly interacting case. In particular, we find that the critical magnetic field for opening the gap becomes an oscillatory function of electron density. [less ▲] Detailed reference viewed: 26 (4 UL)Strongly interacting quantum wires with spin-orbit coupling Pedder, Christopher ; Schmidt, Thomas Scientific Conference (2016, March 10) We study the effect of Rashba spin-orbit coupling on a quantum wire with strong interactions, which can be experimentally realised by depopulating a gated InSb or GaAs wire. When the wire carries a very ... [more ▼] We study the effect of Rashba spin-orbit coupling on a quantum wire with strong interactions, which can be experimentally realised by depopulating a gated InSb or GaAs wire. When the wire carries a very low density of electrons, it is convenient to model the system in terms of a "Wigner crystal" of electrons localised on lattice sites. At the lowest densities, the Wigner crystal is a one dimensional entity, whereas at intermediate regimes it is know that a "zigzag" crystal consisting of two parallel rows of electrons can form. We investigate the effect of Rashba spin-orbit coupling, which plays an important role for both the spin and charge degrees of freedom, in both these systems with and without an applied magnetic field. We propose detection of these effects via measurement of spin-spin correlation functions of the quantum wire, e.g. by doing STM with a polarized tip. [less ▲] Detailed reference viewed: 7 (2 UL)Probing the spin texture of generic helical edge states with an antidot Rod, Alexia ; Dolcetto, Giacomo ; et al Scientific Conference (2016, March 07) Detailed reference viewed: 14 (5 UL)Parafermions in time-reversal invariant topological insulators Schmidt, Thomas Scientific Conference (2016, January) Detailed reference viewed: 16 (2 UL)Detecting and manipulating Majorana bound states in nanowires Schmidt, Thomas Presentation (2016, January) Detailed reference viewed: 16 (1 UL)Parafermions in 2D topological insulators Schmidt, Thomas Presentation (2016, January) Detailed reference viewed: 17 (2 UL)Helical edge states of two-dimensional topological insulators Schmidt, Thomas Presentation (2016, January) Detailed reference viewed: 27 (4 UL)Edge physics in two-dimensional topological insulators Dolcetto, Giacomo ; ; Schmidt, Thomas in La Rivista del Nuovo Cimento (2016) Detailed reference viewed: 96 (2 UL)Detecting and manipulating Majorana bound states in nanowires Schmidt, Thomas Scientific Conference (2016) Detailed reference viewed: 5 (0 UL)Non local quantum state engineering with the Cooper pair splitter beyond the Coulomb blockade regime ; ; et al in Physical Review B (2015), 93 A Cooper pair splitter consists of two quantum dots side-coupled to a conventional superconductor. Usually, the quantum dots are assumed to have a large charging energy compared to the superconducting gap ... [more ▼] A Cooper pair splitter consists of two quantum dots side-coupled to a conventional superconductor. Usually, the quantum dots are assumed to have a large charging energy compared to the superconducting gap, in order to suppress processes other than the coherent splitting of Cooper pairs. In this work, in contrast, we investigate the limit in which the charging energy is smaller than the superconducting gap. This allows us, in particular, to study the effect of a Zeeman field comparable to the charging energy. We find analytically that in this parameter regime the superconductor mediates an inter-dot tunneling term with a spin symmetry determined by the Zeeman field. Together with electrostatically tunable quantum dots, we show that this makes it possible to engineer a spin triplet state shared between the quantum dots. Compared to previous works, we thus extend the capabilities of the Cooper pair splitter to create entangled non local electron pairs. [less ▲] Detailed reference viewed: 8 (1 UL)Parafermion bound states and the fractional Josephson effect in Rashba spin-orbit coupled nanowires Pedder, Christopher ; ; et al Poster (2015, September) Detailed reference viewed: 14 (0 UL) |
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