An investigation of orientational symmetry-breaking mechanisms in high Landau levels

The principal axes of the recently discovered anisotropic phases of 2D elec tron systems at high Landau level occupancy are consistently oriented relat ive to the crystal axes of the host semiconductor. The nature of the native rotational symmetry breaking held responsible for this preferential orient ation remains unknown. Here we report on experiments designed to investigat e the origin and magnitude of this symmetry breaking field. Our results sug gest that neither micron-scale surface roughness features nor the precise s ymmetry of the quantum well potential confining the 2D system are important factors. By combining tilted field transport measurements with detailed se lf-consistent calculations we estimate that the native anisotropy energy, w hatever its origin, is typically similar to1 mK per electron. (C) 2001 Else vier Science Ltd. All rights reserved.