Speaker: Jing Xia, University of California - Irvine
Abstract: In 2 dimensional electron systems (2DES) in GaAs/AlGaAs quantum wells, the N=1 Landau level (LL) exhibits collective electronic phenomena characteristic of both fractional quantum Hall (FQHE) states seen in the lowest LL and anisotropic nematic states in the higher LLs. In particular, fractional quantum Hall effect (FQHE) at I1/2 = 5/2 (and 7/2) is thought to obey non-Abelian statistics and holds the promise of realizing topologically protected quantum computers. Intriguingly, a modest in-plane magnetic field B|| is sufficient to destroy the FQH states at I1/2 = 5/2 (and 7/2) and replace them with anisotropic compressible nematic phases, revealing the close competition between the two. We find that at larger B|| these anisotropic phases I1/2 = 5/2 can themselves be replaced by a new isotropic state, dubbed re-entrant isotropic compressible (RIC) phase . We present strong evidence that this transition is a consequence of the mixing of Landau levels from different electric subbands in the confinement potential. In addition, we find that with B||, the normally isotropic I1/2 = 7/3 FQHE state can transform into an anisotropic phase with an accurately quantized Hall plateau but an anisotropic longitudinal resistivitiescite . As temperature is lowered towards zero, Ixx diminishes while Iyy tends to diverge, reminiscent of the anisotropic nematic states, while surprisingly Ixy and Iyx remain quantized at 3h/7e2, indicating a completely new quantum phase.
 J. Xia, V. Cvicek, J. P. Eisenstein, L. N. Pfeiffer, and K. W. West, Phys Rev Lett 105, 176807 (2010).
 J. Xia, J. P. Eisenstein, L. N. Pfeiffer, and K. W. West, Nature Physics (2011).