Edge effects in an insulating state of an electron-hole system in magnetic field

We find that an InAs/GaSb based electron-hole system exhibits insulating behaviour when the numbers of occupied electron and hole Landau levels are equal. In this insulating state, the Hall resistance becomes symmetric under field reversal, and both the Hall and longitudinal resistances display reproducible fluctuations. We propose a simple model based on edge states to account for these properties, and show that a comparison to the conductivity measured from a Corbino disc is consistent with the model. (C) 2001 Elsevier Science B.V. All rights reserved.