Flicker Noise Induced by Dynamic Impurities in a Quantum Point Contact

TL;DR

This paper models low-frequency noise in a quantum point contact caused by dynamic impurities, revealing that noise levels vary significantly at conductance steps and plateaus, with implications for understanding quantum transport fluctuations.

Contribution

It introduces a new model for low-frequency noise in QPCs based on dynamic defects, deriving a general correlation function applicable to quantized conductance systems.

Findings

LFN is higher at conductance steps than on plateaus.

Noise levels are strongly model-dependent on plateaus.

LFN is weakly model-dependent at conductance steps.

Abstract

We calculate low-frequency noise (LFN) in a quantum point contact (QPC) which is electrostatically defined in a 2D electron gas of a GaAs-AlGaAs heterostructure. The conventional source of LFN in such systems are scattering potentials fluctuating in time acting upon injected electrons. One can discriminate between potentials of different origin -- noise may be caused by the externally applied gate- and source-drain voltages, the motion of defects with internal degrees of freedom close to the channel, electrons hopping between localized states in the doped region, etc. In the present study we propose a model of LFN based upon the assumption that there are many dynamic defects in the surrounding of a QPC. A general expression for the time-dependent current-current correlation function is derived and applied to a QPC with quantized conductance. It is shown that the level of LFN is significantly different at and between the steps in a plot of the conductance vs. gate voltage. On the plateaus, the level of noise is found to be low and strongly model-dependent. At the steps, LFN is much larger and only weakly model-dependent. As long as the system is biased to be at a fixed position relative the conductance step,