Anisotropic States of Two-Dimensional Electron Systems in High Landau Levels: Effect of an In-Plane Magnetic Field

We report the observation of an acute sensitivity of the anisotropic longitudinal resistivity of twodimensional electron systems in half-filled high Landau levels to the magnitude and orientation of an in-plane magnetic field. In the third and higher Landau levels, at filling fractions n 9 2, 11 2, etc., the in-plane field can lead to a striking interchange of the “hard” and “easy” transport directions. In the second Landau level the normally isotropic resistivity and the weak n 5 2 quantized Hall state are destroyed by a large in-plane field and the transport becomes highly anisotropic.