Correlated states of an electron system in a wide quantum well

Magnetotransport experiments on a low-disorder electron system in an 800 Å-wide GaAs quantum well reveal a dramatic evolution from a double- to a single-layer system as the electron density is decreased or the system is made asymmetric. At an intermediate density of 9.7×${10}^{10}$ ${\mathrm{cm}}^{\mathrm{-}2}$, we observe fractional quantum Hall states at Landau level filling factors of ν=3/4, 1/2, and 1/3, with an insulating phase separating the ν=1/2 and 1/3 liquid states. Our data demonstrate that the ν=1/2 state and the insulating phase are most stable in symmetric double-layer systems with appropriate parameters while the ν=1/3 and 3/5 states have a single-layer origin.