arXiv subjects

Takaaki Koga

Publications and source records attributed to Takaaki Koga.

3 recordsLinked to original sources

arXiv2014

Cubic Rashba spin-orbit interaction of two-dimensional hole gas in strained-Ge/SiGe quantum well

The spin-orbit interaction (SOI) of the two-dimensional hole gas in the inversion symmetric semiconductor Ge is studied in a strained-Ge/SiGe quantum well structure. We observed weak anti-localization (WAL) in the magnetoconductivity measurement, revealing that the WAL feature can be fully described by the k-cubic Rashba SOI theory. Furthermore, we demonstrated electric field control of the Rashba SOI. Our findings reveal that the heavy hole (HH) in strained-Ge is a purely cubic-Rashba-system, which is consistent with the spin angular momentum mj = +-3/2 nature of the HH wave function.

cond-mat.mes-hall↗

arXiv2005

Experimental realization of a ballistic spin interferometer based on the Rashba effect using a nanolithographically defined square loop array

The gate-controlled electron spin interference was observed in nanolithographically defined square loop (SL) arrays fabricated using In$_{0.52}$Al$_{0.48}$As/In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As quantum wells. In this experiment, we demonstrate electron spin precession in quasi-one-dimensional channels that is caused by the Rashba effect. It turned out that the spin precession angle $θ$ was gate-controllable by more than 0.75$π$ for a sample with $L=1.5μ$m, where $L$ is the side length of the SL. Large controllability of $θ$ by the applied gate voltage as such is a necessary requirement for the realization of the spin FET device proposed by Datta and Das [Datta {\it et. al.}, Appl. Phys. Lett. {\bf 56}, 665 (1990)] as well as for the manipulation of spin qubits using the Rashba effect.

cond-mat.mes-hall↗

arXiv2004

Spin-orbit induced interference in polygon-structures

We investigate the spin-orbit induced spin-interference pattern of ballistic electrons travelling along any regular polygon. It is found that the spin-interference depends strongly on the Rashba and Dresselhaus spin-orbit constants as well as on the sidelength and alignment of the polygon. We derive the analytical formulae for the limiting cases of either zero Dresselhaus or zero Rashba spin-orbit coupling, including the result obtained for a circle. We calculate the nonzero Dresselhaus and Rashba case numerically for the square, triangle, hexagon, and circle and discuss the observability of the spin-interference which can potentially be used to measure the Rashba and Dresselhaus coefficients.

cond-mat.mes-hall↗