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 similar to3.0x10(11) cm(-2). The temperature dependence of the magnetoresistance R-xx was studied in detail in the vicinity of nu=9/2. In particular, we discovered new minima in R-xx at a filling factor nusimilar or equal to44/5, but only at intermediate temperatures 80less than or similar toTless than or similar to120 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.