Landau velocity for collective quantum Hall breakdown in bilayer graphene

TL;DR

This paper investigates the intrinsic Landau velocity limit for quantum Hall effect breakdown in bilayer graphene, revealing the role of collective excitations and electron interactions through high-frequency noise measurements.

Contribution

It introduces the concept of a Landau critical velocity for QHE breakdown, emphasizing the importance of collective excitations and electron-electron interactions in bilayer graphene.

Findings

Identification of a superpoissonian shot noise signaling breakdown

Demonstration that breakdown is limited by collective excitations

Establishment of a Landau critical velocity analogous to superfluid rotons

Abstract

Breakdown of the quantum Hall effect (QHE) is commonly associated with an electric field approaching the inter Landau-level (LL) Zener field, ratio of the Landau gap and cyclotron radius. Eluded in semiconducting heterostructures, in spite of extensive investigation, the intrinsic Zener limit is reported here using high-mobility bilayer graphene and high-frequency current noise. We show that collective excitations arising from electron-electron interactions are essential. Beyond a noiseless ballistic QHE regime a large superpoissonian shot noise signals the breakdown via inter-LL scattering. The breakdown is ultimately limited by collective excitations in a regime where phonon and impurity scattering are quenched. The breakdown mechanism can be described by a Landau critical velocity as it bears strong similarities with the roton mechanism of superfluids.