Evidence for reentrant striped phases in a two-dimensional hole system

Anisotropic transport is observed at low temperatures in the N=1 and N=2 Landau levels of a very clean two-dimensional (2D) hole system. At $\nu$ = 7/2 and $\nu$ =11/2, the longitudinal magnetoresistance develops strong anisotropies which depend on the direction of current flow and temperature. Interestingly, the transport at $\nu$=9/2 is {\it isotropic} for all temperatures. Our results for a two-dimensional hole system contrast sharply with 2D electron transport where no anisotropy has been observed in the N=1 Landau level, the strongest anisotropy occurs at $\nu$=9/2, and no reentrant behavior is evident.