Nontrivial transition of transmission in a highly open quantum point contact in the quantum Hall regime

TL;DR

This paper reports a universal sharp transition in transmission through a quantum point contact in the quantum Hall regime, which can be modeled phenomenologically and used for electron temperature measurement and quasiparticle charge studies.

Contribution

It introduces a consistent observation of a sharp transmission transition at finite bias in QPCs, fitted by Fermi-Dirac distribution, and proposes a phenomenological model for understanding it.

Findings

Transition observed in all tested QPCs

Transition fits Fermi-Dirac distribution with temperature matching shot-noise thermometry

Similar transitions observed in fractional quantum Hall regime, enabling quasiparticle charge measurement

Abstract

Transmission through a quantum point contact (QPC) in the quantum Hall regime usually exhibits multiple resonances as a function of gate voltage and high nonlinearity in bias. Such behavior is unpredictable and changes sample by sample. Here, we report the observation of a sharp transition of the transmission through an open QPC at finite bias, which was observed consistently for all the tested QPCs. It is found that the bias dependence of the transition can be fitted to the Fermi-Dirac distribution function through universal scaling. The fitted temperature matches quite nicely to the electron temperature measured via shot-noise thermometry. While the origin of the transition is unclear, we propose a phenomenological model based on our experimental results that may help to understand such a sharp transition. Similar transitions are observed in the fractional quantum Hall regime, and it is found that the temperature of the system can be measured by rescaling the quasiparticle energy with the effective charge ($e^*=e/3$). We believe that the observed phenomena can be exploited as a tool for measuring the electron temperature of the system and for studying the quasiparticle charges of the fractional quantum Hall states.