Vanishing thermal equilibration for hole-conjugate fractional quantum Hall states in graphene

TL;DR

This study investigates electrical and thermal conductance in graphene-based quantum Hall states, revealing a surprising lack of thermal equilibration in hole-conjugate fractional quantum Hall phases despite efficient charge equilibration, highlighting complex edge transport phenomena.

Contribution

It provides the first experimental evidence of vanishing thermal equilibration in hole-conjugate fractional quantum Hall states in graphene, supported by theoretical analysis of thermal transport.

Findings

Vanishing thermal equilibration observed at ν=5/3 and ν=8/3

Electrical conductance indicates efficient charge equilibration

Thermal equilibration length diverges in strong interaction limit

Abstract

Transport through edge-channels is responsible for conduction in quantum Hall (QH) phases. Topology dictates quantization of both charge and thermal transport coefficients. These turn out to approach robust quantized values when incoherent equilibration processes become dominant. Here, we report on measurements of both electrical and thermal conductances of integer and fractional quantum Hall (FQH) phases, realized in hBN encapsulated graphite gated bilayer graphene devices. Remarkably, for the complex edge at filling factors $\nu=5/3$ and $\nu=8/3$, which correspond to the paradigmatic hole-conjugate FQH phase $\nu=2/3$ of the partially filled Landau level, we find vanishing thermal equilibration. This is striking, given that, at the same time, our results for the electrical conductance indicate efficient charge equilibration. These results are in accord with our theoretical analysis, pointing to a divergent thermal equilibration length in the limit of strong electrostatic interaction. Our results elucidate the subtle nature of the crossover from mesoscopic to robust topology-dominated transport in electronic two-dimensional topological phases.