Smooth-disorder effects in ballistic microstructures.

We analyze the eeect of weak residual disorder in microstructures deened on high-mobility heterojunctions, where the classical electron motion is ballistic. We parameterize the disorder by its correlation length and the elastic mean-free-path l, which can be estimated from microscopic models. For the experimentally relevant case in which is not negligible with respect to the size of the microstructure, we present a perturbative semiclassical approach demonstrating that the reduction due to disorder of a two-point Green function observable, like the average magnetic susceptibility, is intrinsically diier-ent from the bulk (power-law depending on l and instead of an exponential damping governed uniquely by l). The very weak damping that we obtain supports the use of clean (no disorder) models for the ballistic regime. Our analytical ndings are connrmed by exact numerical calculations.