Strongly Anisotropic Electronic Transport at Landau Level Filling Factor $ν= 9/2$ and $ν= 5/2$ Under Tilted Magnetic Field

We have investigated the influence of an increasing in-plane magnetic field on the states at half-filling of Landau levels ($\nu$ = 11/2, 9/2, 7/2, and 5/2) of a two-dimensional electron system. In the electrically anisotropic phase at $\nu$ = 9/2 and 11/2 an in-plane magnetic field of $\sim$ 1-2 T overcomes its initial pinning to the crystal lattice and {\it reorient} this phase. In the initially isotropic phases at $\nu$ = 5/2 and 7/2 an in-plane magnetic field {\it induces} a strong electrical anisotropy. In all cases, for high in-plane fields, the high resistance axis is parallel to the direction of the in-plane field.