Strongly Anisotropic Electronic Transport at Landau Level Filling Factorν=9/2andν=5/2under a Tilted Magnetic Field

We have investigated the influence of an increasing in-plane magnetic field on the states of half filling of Landau levels ( $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}11/2$, 9/2, 7/2, and 5/2) of a two-dimensional electron system. In the electrically anisotropic phase at $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}9/2$ and 11/2 an in-plane magnetic field of $\ensuremath{\sim}1--2\mathrm{T}$ overcomes its initial pinning to the crystal lattice and reorients this phase. In the initially isotropic phases at $\ensuremath{\nu}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}5/2$ and 7/2 an in-plane magnetic field 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.