Finite-temperature Behavior in the Second Landau Level of the Two-Dimensional Electron Gas

Reports of weak local minima in the magnetoresistance at nu = 2 + 3/5, 2 + 3/7, 2 + 4/9, 2 + 5/9, 2 + 5/7, and 2 + 5/8 in the second Landau level of the electron gas in GaAs/AlGaAs left open the possibility of fractional quantum Hall states at these filling factors. In a high-quality sample we found that the magnetoresistance exhibits peculiar features near these filling factors of interest. These features, however, cannot be associated with fractional quantum Hall states; instead, they originate from magnetoresistive fingerprints of the electronic bubble phases. We found only two exceptions: at nu = 2 + 2/7 and 2 + 5/7 there is evidence for incipient fractional quantum Hall states at intermediate temperatures. As the temperature is lowered, these fractional quantum Hall states collapse due to a phase competition with bubble phases.