  Magnetotransport measurements were performed in a ultra-high mobility
GaAs/AlGaAs quantum well of density $\sim 3.0 \times 10^{11}$ $cm^{-2}$. 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 filling factor $\nu\simeq 4{1/5}$ and $4{4/5}$, but only at
intermediate temperatures $80\lesssim T\lesssim 120$ 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.

Mesoscale and Nanoscale Physics