Competition Between Fractional Quantum Hall Liquid, Bubble and Wigner Crystal Phases in the Third Landau Level

Magnetotransport measurements were performed in a ultra-high 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 ! = 9 2 . In particular, we discovered new minima in Rxx at fi filling factor ! # 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.