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 Rₓₓ was studied in detail in the vicinity of ν=9/2. In particular, we discovered new minima in Rₓₓ at a filling factor ν41/5 and 44/5, but only at intermediate temperatures 80T120 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 $T=0$.