Density-induced reorientation of the stripe at half-filled high Landau levels

The effect of a unidirectional periodic potential on the orientation of the stripe state is studied for the two-dimensional electron system at half-filled high Landau levels. By considering a quantum well with two electric subbands, it is found that the stripe is parallel to the external potential for weak modulation and is orthogonal for strong modulation. In the intermediate range, the orientation of the stripe changes from orthogonal to parallel as the electron density is increased. This result explains the recent experiment performed by J. Zhu {\it et al} that the anisotropy axis at half-filled high Landau levels rotates by $90^0$ by increasing the electron density. It also supports the suggestion that the stripes is pinned by the native surface morphology at the interface of the heterojunction.