Nonlinear transport and noise thermometry in quasi-classical ballistic point contacts

TL;DR

This paper investigates nonlinear transport and noise in quasi-classical ballistic point contacts in a 2D electron system, revealing self-heating effects, extra noise at higher voltages, and the role of electron-electron scattering.

Contribution

It demonstrates the influence of electron-electron interactions on nonlinear transport and noise in ballistic point contacts, introducing a drag-like scattering mechanism.

Findings

Noise temperature is mainly due to Joule heating at low bias.

Extra noise appears at higher bias with decreased differential resistance.

Magnetic field suppresses nonlinear current and noise.

Abstract

We study nonlinear transport and non-equilibrium current noise in quasi-classical point contacts (PCs) defined in a low-density high-quality two-dimensional electron system in GaAs. At not too high bias voltages $V$ across the PC the noise temperature is determined by a Joule heat power and almost independent on the PC resistance that can be associated with a self-heating of the electronic system. This commonly accepted scenario breaks down at increasing $V$, where we observe extra noise accompanied by a strong decrease of the PC's differential resistance. The spectral density of the extra noise is roughly proportional to the nonlinear current contribution in the PC $\delta S\approx2F^*|e\delta I|\sim V^2$ with the effective Fano factor $F^*<1$, indicating that a random scattering process is involved. A small perpendicular magnetic field is found to suppress both $\delta I$ and $\delta S$. Our observations are consistent with a concept of a drag-like mechanism of the nonlinear transport mediated by electron-electron scattering in the leads of quasi-classical PCs.