Density dependent anisotropic phases in a two-dimensional hole system

Anisotropic charge transport is observed in a two-dimensional (2D) hole system in a perpendicular magnetic field at filling factors $\nu $=7/2, $\nu $=11/2, and $\nu $=13/2 at low temperature. In stark contrast, the transport at $\nu $=9/2 is \textit{isotropic} for all temperatures. Our results for a 2D hole system differ substantially from 2D electron transport where no anisotropy has been observed at $\nu $=7/2, and the strongest anisotropy occurs at $\nu $=9/2. Isotropic hole transport at $\nu $=13/2, 11/2 and 7/2 is restored for sufficiently low 2D densities. The density dependence of the observed anisotropies suggests that strong spin-orbit coupling in the hole system contributes to the unusual transport behavior.