We have measured magnetotransport at half-filled high Landau levels in a quantum well with two occupied electric subbands. We find resistivities that are {\em isotropic} in perpendicular magnetic field but become strongly {\em anisotropic} at ν = 9/2 and 11/2 on tilting the field. The anisotropy appears at an in-plane field, Bip∼ 2.5T, with the easy-current direction {\em parallel} to Bip but rotates by 90∘ at Bip∼ 10T and points now in the same direction as in single-subband samples. This complex behavior is in quantitative agreement with theoretical calculations based on a unidirectional charge density wave state model.
@article{arxiv.cond-mat/0003483,
title = {Reorientation of Anisotropy in a Square Well Quantum Hall Sample},
author = {W. Pan and T. Jungwirth and H. L. Stormer and D. C. Tsui and A. H. MacDonald and S. M. Girvin and L. Smrcka and L. N. Pfeiffer and K. W. Baldwin and K. W. West},
journal= {arXiv preprint arXiv:cond-mat/0003483},
year = {2009}
}