Magneto-transport measurements in a clean two-dimensional electron system confined to a wide GaAs quantum well reveal that, when the electrons occupy two electric subbands, the sequences of fractional quantum Hall states observed at high fillings (ν>2) are distinctly different from those of a single-subband system. Notably, when the Fermi energy lies in the ground state Landau level of either of the subbands, no quantum Hall states are seen at the even-denominator ν = 5/2 and 7/2 fillings; instead the observed states are at ν=(i+p/(2p±1)) where i = 2, 3, and p = 1, 2, 3, and include several new states at ν = 13/5, 17/5, 18/5, and 25/7.
@article{arxiv.1004.0979,
title = {Fractional Quantum Hall Effect at High Fillings in a Two-subband Electron System},
author = {J. Shabani and Y. Liu and M. Shayegan},
journal= {arXiv preprint arXiv:1004.0979},
year = {2015}
}