The electronic reconstruction at the interface between two insulating oxides can

No abstract

Topological insulators are characterized by an insulating bulk with a finite band gap and conducting edge or surface states, where charge carriers are protected against backscattering. These states give rise to the quantum spin Hall effect without an external magnetic field, where electrons with opposite spins have opposite momentum at a given edge. The surface energy spectrum of a threedimensional topological insulator is made up by an odd number of Dirac cones with the spin locked to the momentum. The long-sought yet elusive Majorana fermion is predicted to arise from a combination of a superconductor and a topological insulator. An essential step in the hunt for this emergent particle is the unequivocal observation of supercurrent in a topological phase. Here, we present the first measurement of a Josephson supercurrent through a topological insulator. Direct evidence for Josephson supercurrents in superconductor (Nb) - topological insulator (Bi2Te3) - superconductor e-beam fabricated junctions is provided by the observation of clear Shapiro steps under microwave irradiation, and a Fraunhofer-type dependence of the critical current on magnetic field. The dependence of the critical current on temperature and length shows that the junctions are in the ballistic limit. Shubnikov-de Haas oscillations in magnetic fields up to 30 T reveal a topologically non-trivial two-dimensional surface state. We argue that the ballistic Josephson current is hosted by this surface state despite the fact that the normal state transport is dominated by diffusive bulk conductivity. The lateral Nb-Bi2Te3-Nb junctions hence provide prospects for the realization of devices supporting Majorana fermions

We review the emerging field of organic spintronics, where organic materials are applied as a medium to transport and control spin-polarized signals. The contacts for injecting and detecting spins are formed by ferromagnetic metals, oxides, or inorganic semiconductors. First, the basic concepts of spintronics and organic electronics are addressed, and phenomena which are in particular relevant for organic spintronics are highlighted. Experiments using different organic materials, including carbon nanotubes, organic thin films, self-assembled monolayers and single molecules are then reviewed. Observed magnetoresistance points toward successful spin injection and detection, but spurious magnetoresistance effects can easily be confused with spin accumulation. A few studies report long spin relaxation times and lengths, which forms a promising basis for further research. We conclude with discussing outstanding questions and problems.

We consider a single electron in a 1D quantum dot with a static slanting Zeeman field. By combining the spin and orbital degrees of freedom of the electron, an effective quantum two-level (qubit) system is defined. This pseudo-spin can be coherently manipulated by the voltage applied to the gate electrodes, without the need for an external time-dependent magnetic field or spin-orbit coupling. Single qubit rotations and the C-NOT operation can be realized. We estimated relaxation (T1) and coherence (T2) times, and the (tunable) quality factor. This scheme implies important experimental advantages for single electron spin control.PACS numbers: 03.67. Lx, 85.30.Wx, Stimulated by electron-spin-based proposals for quantum computation [1], a growing interest has emerged in realizing the coherent manipulation of a single electron spin in a solid-state environment. The application of the electron's spin -rather than its charge -as a quantum bit (qubit) is motivated by its potentially long coherence time in solids and the fact that it comprises a natural two-level system. Single electron spin resonance (SESR) plays a key role in realizing electron-spin-qubit rotation. Importantly, SESR is also the prime tool for determining the single electron spin coherence time T 2 in confined solid-state systems such as quantum dots (QDs). The induced Rabi oscillations can be read out via electron transport [2] or optically [3], giving an estimate for T 2 . SESR was detected in paramagnetic defects in silicon [4] and for nitrogen vacancies in diamond [5], but not in semiconductor QDs so far. Realizing SESR in QDs is hard, not least because of the necessary high-frequency (∼10 GHz) magnetic field in a cryogenic (∼100 mK) setup. Waveguides and microwave cavities as used in conventional ESR [6], cause serious heating, limiting the operation temperature to ∼1 K. On-going work in our group focuses on generating ac magnetic fields by an on-chip microscopic coil [7].In this Letter, we propose a new SESR scheme that eliminates the need for an externally applied ac magnetic field, and with the potential of very high and tunable quality factors. An ac voltage is applied to let an electron in a QD oscillate under a static slanting Zeeman field. This effectively provides the electron spin with the necessary time-dependent magnetic field. Note the analogy with the Stern-Gerlach experiment, where the spin and orbital degrees of freedom are coupled by employing an inhomogenous magnetic field. The spatial oscillation of the electron within the QD involves the hybridization of orbital states, as schematically depicted in Fig. 1a for the case of the two lowest orbital states, n = 1, 2. Charge qubits based on double QDs [8] offer great tunability, but suffer from short coherence times (∼1 ns) [9]. Spin qubits on the contrary, enable long coherence times(∼1 µs) [10], but are much harder to control, as pointed out above. Here, we present a hybrid chargespin system that is promising both in terms of tunability and coherence. Analogously, the combination of...