Evolution of odd-denominator fractional quantum Hall states in a two-subband system*

Our magneto-transport measurements reveal that the sequence of fractional quantum Hall (FQH) states observed in two-subband, wide GaAs quantum wells at high fillings ($\nu >$ 2) are very different from those of a single-subband system. When the Fermi level lies in the lowest Landau level of either of the two subbands the odd-denominator FQH states following the usual, composite fermion filling sequences are observed. These include states at $\nu $ = 7/3, 8/3, 12/5, 13/5, 10/3, 11/3, 17/5, 18/5, and 25/7. The evolution of these states with changing the Zeeman and subband energies is consistent with coincidences of composite fermion Landau levels.