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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: 101 (2 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: 56 (0 UL)Full counting statistics of Majorana interferometers ; ; Schmidt, Thomas et al in Physica E (2015), 74 We study the full counting statistics of interferometers for chiral Majorana fermions with two incoming and two outgoing Dirac fermion channels. In the absence of interactions, the FCS can be obtained ... [more ▼] We study the full counting statistics of interferometers for chiral Majorana fermions with two incoming and two outgoing Dirac fermion channels. In the absence of interactions, the FCS can be obtained from the 4×4 scattering matrix S that relates the outgoing Dirac fermions to the incoming Dirac fermions. After presenting explicit expressions for the higher-order current correlations for a modified Hanbury Brown–Twiss interferometer, we note that the cumulant-generating function can be interpreted such that unit-charge transfer processes correspond to two independent half-charge transfer processes, or alternatively, to two independent electron-hole conversion processes. By a combination of analytical and numerical approaches, we verify that this factorization property holds for a general SO(4) scattering matrix, i.e. for a general interferometer geometry. [less ▲] Detailed reference viewed: 108 (6 UL)Spin-charge coupling in correlated one-dimensional quantum systems Schmidt, Thomas Scientific Conference (2015, August) Detailed reference viewed: 30 (1 UL)8pi-periodic Josephson effect in time-reversal invariant interacting Rashba nanowires Pedder, Christopher ; ; et al E-print/Working paper (2015) We investigate narrow quantum wires with strong Rashba spin-orbit coupling and electron-electron interactions. We show that virtual transitions between subbands lead to umklapp scattering which can open a ... [more ▼] We investigate narrow quantum wires with strong Rashba spin-orbit coupling and electron-electron interactions. We show that virtual transitions between subbands lead to umklapp scattering which can open a partial gap in the spectrum even in the presence of time-reversal symmetry. Using the superconducting proximity effect to gap out the remaining modes, we show that the system can host zero-energy states at its edges, which are protected by time-reversal symmetry. We present the parameter regime in which these bound states will emerge. Similarly to Majorana bound states, they will produce a zero-bias peak in the differential conductance. In contrast to the Majorana fermions, however, their fourfold degeneracy leads to an 8π periodicity of the Josephson current due to tunneling of fractionalized excitations with charge e/2. [less ▲] Detailed reference viewed: 133 (4 UL)Finite-temperature conductance of interacting quantum wires with Rashba spin-orbit coupling Schmidt, Thomas Poster (2015, July) Detailed reference viewed: 83 (1 UL)Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation Schmidt, Thomas Scientific Conference (2015, July) Detailed reference viewed: 88 (0 UL)Tunneling between helical Majorana modes and helical Luttinger liquids ; Schmidt, Thomas ; in Physical Review B (2015), 91 We propose and study the charge transport through single and double quantum point contacts setup between helical Majorana modes and an interacting helical Luttinger liquid. We show that the differential ... [more ▼] We propose and study the charge transport through single and double quantum point contacts setup between helical Majorana modes and an interacting helical Luttinger liquid. We show that the differential conductance decreases for stronger repulsive interactions and that the point contacts become insulating above a critical interaction strength. For a single-point contact, the differential conductance as a function of bias voltage shows a series of peaks due to Andreev reflection of electrons in the Majorana modes. In the case of two point contacts, interference phenomena make the structure of the individual resonance peaks less universal and show modulations with different separation distance between the contacts. For small separation distance, the overall features remain similar to the case of a single-point contact. [less ▲] Detailed reference viewed: 101 (1 UL)Parafermions in time-reversal invariant topological insulators Schmidt, Thomas Presentation (2015, June) Detailed reference viewed: 30 (0 UL)Spin texture of generic helical edge states Rod, Alexia ; Schmidt, Thomas ; in Physical Review B (2015), 91 We study the spin texture of a generic helical liquid, the edge modes of a two-dimensional topological insulator with broken axial spin symmetry. By considering honeycomb and square-lattice realizations ... [more ▼] We study the spin texture of a generic helical liquid, the edge modes of a two-dimensional topological insulator with broken axial spin symmetry. By considering honeycomb and square-lattice realizations of topological insulators, we show that in all cases the generic behavior of a momentum-dependent rotation of the spin quantization axis is realized. Here we establish this mechanism also for disk geometries with continuous rotational symmetry. Finally, we demonstrate that the rotation of spin-quantization axis remains intact for arbitrary geometries, i.e., in the absence of any continuous symmetry. We also calculate the dependence of this rotation on the model and material parameters. Finally, we propose a spectroscopy measurement which should directly reveal the rotation of the spin-quantization axis of the helical edge states. [less ▲] Detailed reference viewed: 143 (20 UL)Detecting and manipulating Majorana bound states in nanowires Schmidt, Thomas Presentation (2015, June) Detailed reference viewed: 36 (0 UL)Z4 parafermions in time-reversal invariant topological insulators Schmidt, Thomas Presentation (2015, June) Detailed reference viewed: 56 (0 UL)Z4 parafermions in time-reversal invariant topological insulators Schmidt, Thomas Scientific Conference (2015, April) Detailed reference viewed: 50 (0 UL)Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation Schmidt, Thomas Scientific Conference (2015, March) Detailed reference viewed: 71 (0 UL)Non-Abelian parafermions in time-reversal invariant interacting helical systems ; ; et al in Phys. Rev. B (2015), 91 The interplay between bulk spin-orbit coupling and electron-electron interactions produces umklapp scattering in the helical edge states of a two-dimensional topological insulator. If the chemical ... [more ▼] The interplay between bulk spin-orbit coupling and electron-electron interactions produces umklapp scattering in the helical edge states of a two-dimensional topological insulator. If the chemical potential is at the Dirac point, umklapp scattering can open a gap in the edge state spectrum even if the system is time-reversal invariant. We determine the zero-energy bound states at the interfaces between a section of a helical liquid which is gapped out by the superconducting proximity effect and a section gapped out by umklapp scattering. We show that these interfaces pin charges which are multiples of $e/2$, giving rise to a Josephson current with $8\pi$ periodicity. Moreover, the bound states, which are protected by time-reversal symmetry, are fourfold degenerate and can be described as $Z_4$ parafermions. We determine their braiding statistics and show how braiding can be implemented in topological insulator systems. [less ▲] Detailed reference viewed: 116 (4 UL)Detecting nonlocal Cooper pair entanglement by optical Bell inequality violation ; ; et al in Physical Review. B : Condensed Matter (2015), 91 Based on the Bardeen Cooper Schrieffer (BCS) theory of superconductivity, the coherent splitting of Cooper pairs from a superconductor to two spatially separated quantum dots has been predicted to ... [more ▼] Based on the Bardeen Cooper Schrieffer (BCS) theory of superconductivity, the coherent splitting of Cooper pairs from a superconductor to two spatially separated quantum dots has been predicted to generate nonlocal pairs of entangled electrons. In order to test this hypothesis, we propose a scheme to transfer the spin state of a split Cooper pair onto the polarization state of a pair of optical photons. We show that the produced photon pairs can be used to violate a Bell inequality, unambiguously demonstrating the entanglement of the split Cooper pairs. [less ▲] Detailed reference viewed: 101 (1 UL)Electron transport in multiterminal networks of Majorana bound states ; ; Schmidt, Thomas in Phys. Rev. B (2014), 90 We investigate electron transport through multiterminal networks hosting Majorana bound states (MBS) in the framework of full counting statistics. In particular, we apply our general results to T-shaped ... [more ▼] We investigate electron transport through multiterminal networks hosting Majorana bound states (MBS) in the framework of full counting statistics. In particular, we apply our general results to T-shaped junctions of two Majorana nanowires. When the wires are in the topologically nontrivial regime, three MBS are localized near the outer ends of the wires, while one MBS is localized near the crossing point, and when the lengths of the wires are finite adjacent MBS can overlap. We propose a combination of current and cross-correlation measurements to reveal the predicted coupling of four Majoranas in a topological T junction. Interestingly, we show that the elementary transport processes at the central lead are different compared to the outer leads, giving rise to characteristic nonlocal signatures in electronic transport. We find quantitative agreement between our analytical model and numerical simulations of a tight-binding model. Using the numerical simulations, we discuss the effect of weak disorder on the current and the cross-correlation functions. [less ▲] Detailed reference viewed: 100 (2 UL)Structure factor of interacting one-dimensional helical systems ; Schmidt, Thomas ; in Phys. Rev. B (2014), 89 We calculate the dynamical structure factor $S(q,\omega)$ of a weakly interacting helical edge state in the presence of a magnetic field $B$. The latter opens a gap of width $2B$ in the single-particle ... [more ▼] We calculate the dynamical structure factor $S(q,\omega)$ of a weakly interacting helical edge state in the presence of a magnetic field $B$. The latter opens a gap of width $2B$ in the single-particle spectrum, which becomes strongly nonlinear near the Dirac point. For chemical potentials $|\mu|>B$, the system then behaves as a nonlinear helical Luttinger liquid, and a mobile-impurity analysis reveals power-law singularities in $S(q,\omega)$ which depend on the interaction strength as well as on the spin texture of the edge states. For $|\mu|<B$, the low-energy excitations are gapped, and we determine $S(q,\omega)$ by using an analogy to exciton physics. [less ▲] Detailed reference viewed: 69 (3 UL)Josephson effect in normal and ferromagnetic topological-insulator junctions: Planar, step, and edge geometries ; Schmidt, Thomas ; et al in Phys. Rev. B (2014), 90 We investigate Josephson junctions on the surface of a three-dimensional topological insulator in planar, step, and edge geometries. The elliptical nature of the Dirac cone representing the side surface ... [more ▼] We investigate Josephson junctions on the surface of a three-dimensional topological insulator in planar, step, and edge geometries. The elliptical nature of the Dirac cone representing the side surface states of the topological insulator results in a scaling factor in the Josephson current in a step junction as compared to the planar junction. In edge junctions, the contribution of the Andreev bound states to the Josephson current vanishes due to spin-momentum locking of the surface states. Furthermore, we consider a junction with a ferromagnetic insulator between the superconducting regions. In these ferromagnetic junctions, we find an anomalous finite Josephson current at zero phase difference if the magnetization is pointing along the junction (and perpendicular to the Josephson current). An out-of-plane magnetization with respect to the central region of the junction opens up an exchange gap and leads to a nonmonotonic behavior of the critical Josephson current for sufficiently large magnetization as the chemical potential increases. [less ▲] Detailed reference viewed: 95 (1 UL)Detecting an exciton crystal by statistical means ; ; Schmidt, Thomas et al in Physica B (2014), 441 We investigate an ensemble of excitons in a coupled quantum well excited via an applied laser field. Using an effective disordered quantum Ising model, we perform a numerical simulation of the ... [more ▼] We investigate an ensemble of excitons in a coupled quantum well excited via an applied laser field. Using an effective disordered quantum Ising model, we perform a numerical simulation of the experimental procedure and calculate the probability distribution function P(M) to create M excitons as well as their correlation function. It shows clear evidence of the existence of two phases corresponding to a liquid and a crystal phase. We demonstrate that not only the correlation function but also the distribution P(M) is very well suited to monitor this transition. [less ▲] Detailed reference viewed: 63 (1 UL) |
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