Extracting net current from an upstream neutral mode in the fractional quantum Hall regime

TL;DR

This study demonstrates a novel method to detect upstream neutral modes in fractional quantum Hall states by measuring thermo-electric current through a quantum dot, providing insights into edge mode interactions.

Contribution

It introduces a straightforward approach to study upstream neutral modes using thermo-electric measurements, avoiding complex noise measurement techniques.

Findings

Neutral modes heat the quantum dot, generating a measurable thermo-electric current.

The thermo-electric current vanishes above 110mK, indicating neutral mode decay.

Method offers a simpler alternative for probing neutral modes in quantum Hall systems.

Abstract

Upstream neutral modes, counter propagating to charge modes and carrying energy without net charge, had been predicted to exist in some of the fractional quantum Hall states and were recently observed via noise measurements. Understanding such modes will assist in identifying the wavefunction of these states, as well as shedding light on the role of Coulomb interactions within edge modes. In this work, performed mainly in the nu=2/3 state, we placed a quantum dot a few micrometers upstream of an ohmic contact, which served as a neutral modes source. We showed the neutral modes heat the input of the dot, causing a net thermo-electric current to flow through it. Heating of the electrons led to a decay of the neutral mode, manifested in the vanishing of the thermo-electric current at T>110mK. This setup provides a straightforward method to investigate upstream neutral modes without turning to the more cumbersome noise measurements.