Integer quantum Hall states in coupled double electron gas systems at mismatched carrier densities

Abstract

We have used gated double two-dimensional electron gas (2DEG) samples in a study of the integer quantum Hall effect at mismatched carrier densities. For weakly coupled samples, the Landau level occupancy associated with the upper and lower 2DEGs may be identified for all gate voltages and magnetic fields. Strong integer states are only seen when an integer number of Landau levels are occupied in each subband. The strongly coupled sample has two magnetic field regimes with differing behaviour. At low fields, the quantum Hall states associated with two subbands are seen, and the device behaviour is similar to that of the weakly coupled sample, whilst at high fields, quantum Hall states are observed which are continuous over the full range of mismatched densities. The magnetic fields at which these quantum Hall states are seen correspond to the total number of carriers in the two subbands filling an integer number of Landau levels. Our studies show that the observed transition is driven by the degree of coupling between the 2DEGs rather than the inter-layer separation.