W. Pan, K. W. Baldwin, K. W. West, L. N. Pfeiffer, D. C. Tsui
We present here the results from a density dependent study of the activation energy gaps of the fractional quantum Hall effect states at Landau level fillings \nu=8/3 and 7/3 in a series of high quality quantum wells. In the density range from 0.5 x 10^{11} to 3 x 10^{11} cm^{-2}, the 7/3 energy gap increases monotonically with increasing density, supporting its ground state being spin polarized. For the 8/3 state, however, its energy gap first decreases with increasing density, almost vanishes at n ~ 0.8 x 10^{11} cm^{-2}, and then turns around and increases with increasing density, clearly demonstrating a spin transition.
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http://arxiv.org/abs/1204.0557
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