Many-body interactions, the quantum Hall effect, and insulating phases in bilayer two-dimensional hole-gas systems

Abstract

We have studied the quantum Hall effect in a high mobility double-layer 2D hole gas in which we are able to control the carrier density in the two layers independently. We find that both the ν=1 and the ν= 3 2 bilayer quantum Hall (QH) states are destroyed with increasing carrier density. The collapse of ν=1 is extremely abrupt, occurring at a carrier density that corresponds to an inter-layer separation of 1.8 l B . However, although the ν= 3 2 QH state disappears without trace, the zero in ρ xx at ν=1 is replaced by a broad minimum similar to that observed at ν= 1 2 when only one layer is occupied. This suggests that we are observing a transition from a correlated incompressible QH state with total filling factor ν=1 to a compressible state consisting of two (possibly uncorrelated) layers of ‘composite fermions’. At very low densities and filling factors below ν=1, an insulating phase is observed, which is not present when only one layer is occupied. We demonstrate that this state is entirely due to inter-layer interactions and is strong evidence for the existence of a bilayer Wigner crystal.