Edge channels and the role of contacts in the quantum Hall regime

The vanishing voltage drop ${\mathit{U}}_{\mathit{x}\mathit{x}}$ in the quantum Hall regime is destroyed if barriers with reduced filling factors are introduced between the potential probes. We investigated a system with two barriers created by Schottky gates that are separated by up to 200 μm. Two metallic contacts could be electrically connected or disconnected to the system in the region between the barriers. The change from adiabatic to equilibrated transport demonstrates the importance of Ohmic contacts as energy and phase-randomizing reservoirs. The experiments show strong evidence for current-carrying edge states.