We present activation gap measurements of the fractional quantum Hall effect (FQHE) in the second Landau level. Signatures for 14 (5) distinct incompressible FQHE states are seen in a high (low) mobility sample with the enigmatic 5/2 even denominator FQHE having a large activation gap of ∼600 (∼300mK) in the high (low) mobility sample. Our measured large relative gaps for 5/2, 7/3, and 8/3 FQHE indicate emergence of exotic FQHE correlations in the second Ladau level, possibly quite different from the well-known lowest Landau level Laughlin correlations. Our measured 5/2 gap is found to be in reasonable agreement with the theoretical gap once finite width and disorder broadening corrections are taken into account.
@article{arxiv.0707.0236,
title = {Fractional Quantum Hall Effect in the Second Landau Level},
author = {H. C. Choi and W. Kang and S. Das Sarma and L. N. Pfeiffer and K. W. West},
journal= {arXiv preprint arXiv:0707.0236},
year = {2009}
}