Spin transition in the second Landau level*

The fractional quantum Hall effect (FQHE) states in the second Landau level have attracted growing interest and intensive theoretical and experimental investigations due to their being non-Abelian states. Recently, we systematically examined the spin polarization of the 8/3 and 12/5 states in a series of high quality two dimensional electron systems. Evidence of spin transition was observed for both states, suggesting a more complicated nature of the FQHE ground states in the second Landau level.