Dynamics of density imbalanced bilayer holes in the quantum Hall regime

Abstract

We report magnetotransport measurements on bilayer GaAs hole systems with unequal hole concentrations in the two layers. At magnetic fields where one layer is in the integer quantum Hall state and the other has bulk extended states at the Fermi energy, the longitudinal and the Hall resistances of the latter are hysteretic, in agreement with previous measurements. For a fixed magnetic field inside this region and at low temperatures $(T\ensuremath{\le}350\text{ }\text{mK})$, the time evolutions of the longitudinal and Hall resistances show pronounced jumps followed by slow relaxations, with no end to the sequence of jumps. Our measurements demonstrate that the jumps occur simultaneously in pairs of contacts $170\text{ }\ensuremath{\mu}\text{m}$ apart and appear to involve changes in the charge configuration of the bilayer. In addition, the jumps can occur with either random or regular periods, excluding thermal fluctuations as a possible origin for the jumps. Finally, while remaining at a fixed field, we warm the sample to above 350 mK, where the jumps disappear. Upon recooling the sample below this temperature, the jumps reappear, indicating that the jumps do not result from nearly dissipationless eddy currents either.