Electron transport in quantum channels with spin-orbit interaction: Effects of the sign of the Rashba coupling and applications to nanowires

TL;DR

This paper studies how the sign of Rashba spin-orbit coupling affects electron transport in quantum nanowires, revealing conditions where the conductance depends on the RSOC sign and where it does not, with implications for nanoscale device design.

Contribution

It demonstrates the impact of RSOC sign in inhomogeneous nanowires and provides a realistic setup analysis for experimental applications.

Findings

Transmission is nearly perfect when RSOC signs are equal.

Opposite RSOC signs suppress electron transmission.

Conductance behavior varies with RSOC sign and distance between regions.

Abstract

We investigate the effects of the sign of the Rashba spin-orbit coupling (RSOC) on electron transmission through a single-channel Nanowire (NW) in the quantum coherent regime. We show that, while for a finite length NW with homogeneous RSOC contacted to two electrodes the sign of its RSOC does not affect electron transport, the situation can be quite different in the presence of an inhomogeneous RSOC and a magnetic field applied along the NW axis. By analyzing transport across an interface between two regions of different RSOC we find that, if the two regions have equal RSOC signs, the transmission within the magnetic gap energy range is almost perfect, regardless of the ratio of the spin-orbit energies to the Zeeman energy. In contrast, when the two regions have opposite RSOC signs and are Rashba-dominated, the transmission gets suppressed. Furthermore, we discuss the implementation on a realistic NW setup where two RSOC regions are realized with suitably coupled gates separated by a finite distance. We find that the low-temperature NW conductance exhibits a crossover from a short distance behavior that strongly depends on the relative RSOC sign of the two regions to a large distance oscillatory behavior that is independent of such relative sign. We are thus able to identify the conditions where the NW conductance mainly depends on the sign of the RSOC and the ones where only the RSOC magnitude matters.