Vanishing Thermal Equilibration for Hole-Conjugate Fractional Quantum Hall States in Graphene

Transport through edge channels is responsible for conduction in quantum Hall (QH) phases. Robust quantized values of charge and thermal conductances dictated by bulk topology appear when equilibration processes become dominant. We report on measurements of electrical and thermal conductances of integer and fractional QH phases, realized in hexagonal boron nitride encapsulated graphite-gated bilayer graphene devices for both electron and hole doped sides with different valley and orbital symmetries. Remarkably, for complex edges at filling factors ν=53 and 83, closely related to the paradigmatic hole-conjugate ν=23 phase, we find quantized thermal conductance whose values (3κ0T and 4κ0T, respectively where κ0T is the thermal conductance quantum) are markedly inconsistent with the values dictated by topology (1κ0T and 2κ0T, respectively). The measured thermal conductance values remain insensitive to different symmetries, suggesting its universal nature. Our findings are supported by a theoretical analysis, which indicates that, whereas electrical equilibration at the edge is established over a finite length scale, the thermal equilibration length diverges for strong electrostatic interaction. Our results elucidate the subtle nature of crossover from coherent, mesoscopic to topology-dominated transport.Received 21 December 2020Accepted 20 April 2021DOI:https://doi.org/10.1103/PhysRevLett.126.216803© 2021 American Physical SocietyPhysics Subject Headings (PhySH)Research AreasBallistic transportComposite fermionsEdge statesFractional quantum Hall effectInteger quantum Hall effectThermal conductivityPhysical SystemsGrapheneTechniquesLithographyPlasma etchingCondensed Matter, Materials & Applied Physics