Lateral spin-orbit interaction and spin polarization in quantum point contacts

TL;DR

This paper demonstrates that asymmetric lateral confinement in quantum point contacts induces controllable spin polarization without magnetic fields, offering new ways to generate spin-polarized currents and explaining certain conductance phenomena.

Contribution

It reveals how lateral spin-orbit coupling from asymmetric potentials can produce spin polarization in quantum point contacts without external magnetic fields.

Findings

Non-zero spin polarization achieved without magnetic fields.

Dependence of polarization on structural asymmetry and magnetic fields.

Potential explanation for 0.5 conductance plateau in InAs quantum wells.

Abstract

We study ballistic transport through semiconductor quantum point contact systems under different confinement geometries and applied fields. In particular, we investigate how the {\em lateral} spin-orbit coupling, introduced by asymmetric lateral confinement potentials, affects the spin polarization of the current. We find that even in the absence of external magnetic fields, a variable {\em non-zero spin polarization} can be obtained by controlling the asymmetric shape of the confinement potential. These results suggest a new approach to produce spin polarized electron sources and we study the dependence of this phenomenon on structural parameters and applied magnetic fields. This asymmetry-induced polarization provides also a plausible explanation of our recent observations of a 0.5 conductance plateau (in units of $2e^2/h$) in quantum point contacts made on InAs quantum-well structures. Although our estimates of the required spin-orbit interaction strength in these systems do not support this explanation, they likely play a role in the effects enhanced by electron-electron interactions.