Tomohiro Yokoyama

Anomalous Josephson effect induced by spin-orbit interaction and Zeeman effect in semiconductor nanowires

We investigate theoretically the Josephson junction of semiconductor nanowire with strong spin-orbit (SO) interaction in the presence of magnetic field. By using a tight-binding model, the energy levels En of Andreev bound states are numerically calculated as a function of phase difference ? between two superconductors in the case of short junctions. The dc Josephson current is evaluated from the Andreev levels. In the absence of SO interaction, a 0-? transition due to the magnetic field is clearly observed. In the presence of SO interaction, the coexistence of SO interaction and Zeeman effect results in En(??)?En(?), where the anomalous Josephson current flows even at ?=0. In addition, the direction dependence of critical current is observed, in accordance with experimental results.

Josephson Current through Semiconductor Nanowire with Spin-Orbit Interaction in Magnetic Field

We theoretically study the DC Josephson effect of a semiconductor nanowire (NW) with a strong spin–orbit interaction when a magnetic field is applied parallel to the NW. We adopt a model of single scatterer in a quasi-one-dimensional system for short junctions where the size of a normal region is much smaller than the coherent length. In the case of a single conduction channel, we obtain analytical expressions for the energy levels of Andreev bound states \(E_{n}\) and supercurrent as a function of the phase difference \(\varphi\) between two superconductors. We show the 0–π transition by tuning the magnetic field. In the case of more than one conduction channel, we find that \(E_{n} (-\varphi ) \neq E_{n} (\varphi )\) from the interplay between the spin–orbit interaction and Zeeman effect, which results in a finite supercurrent at \(\varphi =0\) (anomalous Josephson current) and a direction-dependent critical current.

Quantum dot spin filter in resonant tunneling and Kondo regimes

A quantum dot with spin–orbit interaction can work as an efficient spin filter if it is connected to N (≥3) external leads via tunnel barriers. When an unpolarized current is injected to a quantum dot from a lead, polarized currents are ejected to other leads. A two-level quantum dot is examined as a minimal model. First, we show that the spin polarization is markedly enhanced by resonant tunneling when the level spacing in the dot is smaller than the level broadening. Next, we examine the many-body resonance induced by the Kondo effect in the Coulomb blockade regime. A large spin current is generated in the presence of the SU(4) Kondo effect when the level spacing is less than the Kondo temperature.

Enhanced Spin Hall Effect in Semiconductor Heterostructures with Artificial Potential

We theoretically investigate the extrinsic spin Hall effect (SHE) in semiconductor heterostructures, caused by scattering at an artificial potential created by an antidot, STM tip, etc. The potential is electrically tunable. First, we formulate the SHE in terms of phase shifts in the partial wave expansion for a two-dimensional electron gas. The effect is significantly enhanced by resonant scattering when the attractive potential is properly tuned. Second, we examine a three-terminal device including an antidot, which possibly produces a spin current with a polarization of more than 50%.

Efficient spin filter using multi-terminal quantum dot with spin-orbit interaction.

We propose a multi-terminal spin filter using a quantum dot with spin-orbit interaction. First, we formulate the spin Hall effect (SHE) in a quantum dot connected to three leads. We show that the SHE is significantly enhanced by the resonant tunneling if the level spacing in the quantum dot is smaller than the level broadening. We stress that the SHE is tunable by changing the tunnel coupling to the third lead. Next, we perform a numerical simulation for a multi-terminal spin filter using a quantum dot fabricated on semiconductor heterostructures. The spin filter shows an efficiency of more than 50% when the conditions for the enhanced SHE are satisfied.PACS numbers: 72.25.Dc,71.70.Ej,73.63.Kv,85.75.-d

Generation of spin-polarized current using multiterminal quantum dot with spin-orbit interaction

We theoretically examine generation of spin-polarized current using multi-terminated quantum dot with spin-orbit interaction. First, a two-level quantum dot is analyzed as a minimal model, which is connected to

Effect of Spin–Orbit Interaction on Supercurrent in Semiconductor Nanowire

N

Asymmetric current-phase relation due to spin-orbit interaction in semiconductor nanowire Josephson junction

(

Two-terminal spin filter using quantum dot with spin-orbit interaction in magnetic field

\ge 2

Spin Hall Effect Enhanced by Kondo Resonance in Semiconductor Quantum Dot

) external leads via tunnel barriers. When an unpolarized current is injected to the quantum dot from a lead, a polarized current is ejected to others, similarly to the spin Hall effect. In the absence of magnetic field, the generation of spin-polarized current requires