Noise processes in InAs/Ga(In)Sb Corbino structures

Abstract

Two-dimensional topological insulators are of great interest, with predicted topological protection of one-dimensional helical edge states at their boundaries. Shot noise, the fluctuations in driven current due to the discreteness of charge carriers, has been proposed as a way of distinguishing between trivial and nontrivial edge state conduction, as well as a means of assessing back-scattering mechanisms in the latter. Such measurements require an understanding of possible contributions to the noise from contacts and conduction in the 2D bulk. We present noise measurements in Corbino structures based on InAs/Ga(In)Sb quantum well interfaces over a broad temperature and applied current range. As the temperature is lowered and the bulk transport is gapped out, shot noise becomes detectable in these two-terminal devices, in both high- and low-frequency measurement techniques. Quantitative comparison with a noise model shows that the total applied voltage drop is split among the contacts and the bulk and that the devices have some intrinsic asymmetry. Within that model, the magnitude of the shot noise appears to be anomalously large, implying the contacts to the 2D bulk are nontrivial in this system.