Metal-insulator oscillations in a two-dimensional electron-hole system

The electrical transport properties of a bipolar InAs/GaSb system have been studied in a magnetic field. The resistivity oscillates between insulating and metallic behavior while the quantum Hall effect shows a digital charac ter oscillating from 0 to 1 conductance quantum e(2)/h. The insulating beha vior is attributed to the formation of a total energy gap in the system. A novel looped edge state picture is proposed associated with the appearance of a voltage between Hall probes which is symmetric on magnetic field rever sal.