Breakdown of quantized conductance in point contacts calculated using realistic potentials.

Abstract

Ionized donors in a heterostructure generate a random potential with long-ranged fluctuations. We have used realistic self-consistent potentials to study its effect on the quantized conductance of point contacts, and find that transport in confined and unconfined geometries probe complementary aspects of the random potential. Thus quantization breaks down when the length of the point contact exceeds 1/2 \ensuremath{\mu}m, an order of magnitude less than the mean free path in the bulk. The characteristics reflect the detailed configuration of impurities near the point contact.