Possible origin of the 0.5 plateau in the ballistic conductance of quantum point contacts

TL;DR

This study uses NEGF formalism to show that lateral spin-orbit coupling and electron interactions in quantum point contacts can produce a robust 0.5 conductance plateau due to spontaneous spin polarization, aligning with experimental observations.

Contribution

It demonstrates that the 0.5 conductance plateau arises from spontaneous spin polarization enhanced by electron interactions, without external magnetic fields.

Findings

0.5G0 conductance plateau is robust up to 40K.

Spin polarization can be reversed by bias polarity.

Results agree with experiments on InAs QPCs.

Abstract

A non-equilibrium Green function formalism (NEGF) is used to study the conductance of a side-gated quantum point contact (QPC) in the presence of lateral spin-orbit coupling (LSOC). A small difference of bias voltage between the two side gates (SGs) leads to an inversion asymmetry in the LSOC between the opposite edges of the channel. In single electron modeling of transport, this triggers a spontaneous but insignificant spin polarization in the QPC. However, the spin polarization of the QPC is enhanced substantially when the effect of electron-electron interaction is included. The spin polarization is strong enough to result in the occurrence of a conductance plateau at 0.5G0 (G0 = 2e2/h) in the absence of any external magnetic field. In our simulations of a model QPC device, the 0.5 plateau is found to be quite robust and survives up to a temperature of 40K. The spontaneous spin polarization and the resulting magnetization of the QPC can be reversed by flipping the polarity of the source to drain bias or the potential difference between the two SGs. These numerical simulations are in good agreement with recent experimental results for side-gated QPCs made from the low band gap semiconductor InAs.