Counterflowing edge current and its equilibration in quantum Hall devices with sharp edge potential: Roles of incompressible strips and contact configuration

摘要

We report the observation of counterflowing edge current in InAs quantum wells which leads to the breakdown of quantum Hall (QH) effects at high magnetic fields. Counterflowing edge channels arise from the Fermi-level pinning of InAs and the resultant sharp edge potential with downward bending. By measuring the counterflow conductance for varying edge lengths, we determine the effective number N-C of counterflowing modes and their equilibration length lambda(eq) at a bulk integer filling factor nu = 1-4 lambda(eq) increased exponentially with magnetic field B, reaching 200 mu m for nu = 4 at B >= 7.6 T. Our data reveal important roles of the innermost incompressible strip with even filling in determining N-C and lambda(eq) and the impact of the contact configuration on the QH effect breakdown. Our results show that counterflowing edge channels manifest as transport anomalies only at high fields and in short edges. This in turn suggests that, even in the integer QH regime, the actual microscopic structure of the edge states can differ from that anticipated from macroscopic transport measurements, which is relevant to various systems including atomic-layer materials.