Anamolous conductance plateau in an asymmetrically biased InAs/InAlAs quantum point contact

TL;DR

This study investigates an anomalous conductance plateau at 0.4 in an InAs/InAlAs quantum point contact, revealing its dependence on gate bias asymmetry, surface roughness effects, and magnetic confinement at low temperature.

Contribution

It demonstrates the emergence of a spin-polarization related conductance plateau under specific bias asymmetry conditions in an InAs-based QPC, highlighting the role of magnetic fields and surface scattering.

Findings

Anomalous conductance plateau appears at 0.4 in units of 2e^2/h.

Plateau is observed over a 1V bias asymmetry range.

Magnetic field enhances ballistic transport by reducing surface scattering.

Abstract

The appearance and evolution of an anomalous conductance plateau at 0.4 (in units of 2e2/h) in an In0.52Al0.48As/InAs quantum point contact (QPC), in the presence of lateral spin-orbit coupling, has been studied at T=4.2K as a function of the potential asymmetry between the in-plane gates of the QPC. The anomalous plateau, a signature of spin polarization in the channel, appears only over an intermediate range (around 3 V) of bias asymmetry. It is quite robust, being observed over a maximum range of nearly 1V of the sweep voltage common to the two in-plane gates. Our conductance measurements show evidence of surface roughness scattering from the side walls of the QPC. We show that a strong perpendicular magnetic field leads to magnetic confinement in the channel which reduces the importance of scattering from the side walls and favors the onset of near ballistic transport through the QPC.