  We report magnetotransport properties of a two-dimensional electron gas
confined at MgZnO/ZnO heterointerface in a high magnetic field up to 26 T. High
electron mobility and low charge carrier density enabled the observation of the
fractional quantum Hall state nu = 1/3. For an even lower charge carrier
density, we observe a transition from quantum Hall liquid to an insulator below
the filling factor 1/3. Because of the large electron effective mass in ZnO, we
suggest the MgZnO/ZnO heterostructure to be a prototype system for highly
correlated quantum Hall physics.
