Spin Polarization of the 12/5 Fractional Quantum Hall Effect
  We have carried out tilt magnetic field (B) studies of the \nu=12/5 fractional quantum Hall state in an ultra-high quality GaAs quantum well specimen. Its diagonal magneto-resistance Rxx shows a non-monotonic dependence on tilt angle (\theta). It first increases sharply with increasing \theta, reaches a maximal value of ~ 70 ohms at \theta ~ 14^o, and then decreases at higher tilt angles. Correlated with this dependence of Rxx on \theta, the 12/5 activation energy (\Delta_{12/5}) also shows a non-monotonic tilt dependence. \Delta_{12/5} first decreases with increasing \theta. Around \theta = 14^{o}, \Delta_{12/5} disappears as Rxx becomes non-activated. With further increasing tilt angles, \Delta_{12/5} reemerges and increases with \theta. This tilt B dependence at \nu=12/5 is strikingly different from that of the well-documented 5/2 state and calls for more investigations on the nature of its ground state. 
Chi Zhang, Chao Huan, J. S. Xia, N. S. Sullivan, W. Pan, K.W. Baldwin,   K. W. West, L. N. Pfeiffer, and D. C. Tsui
cond-mat.mes-hall