Spin transition in the ν=8/3 fractional quantum hall effect

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 ν=8/3 and 7/3 in a series of high quality quantum wells. In the density range from 0.5×1011 to 3×1011cm ^-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. 8×1011cm ^-2, and then turns around and increases with increasing density, clearly demonstrating a spin transition.