Competition between a Fractional Quantum Hall Liquid and Bubble and Wigner Crystal Phases in the Third Landau Level

Magnetotransport measurements were performed in an ultrahigh mobility GaAs/AlGaAs quantum well of density ∼3.0×10¹¹  cm^-2. The temperature dependence of the magnetoresistance R_xx was studied in detail in the vicinity of ν=9/2. In particular, we discovered new minima in R_xx at a filling factor ν≃41/5 and 44/5, but only at intermediate temperatures 80≲T≲120  mK. We interpret these as evidence for a fractional quantum Hall liquid forming in the N=2 Landau level and competing with bubble and Wigner crystal phases favored at lower temperatures. Our data suggest that a magnetically driven insulator-insulator quantum phase transition occurs between the bubble and Wigner crystal phases at T=0.