The effect of a non‐uniform scattering potential on conductance fluctuations in a quantum wire

Abstract

We investigate experimentally the fluctuations of the conductance of a high mobility quantum wire. We show that scattering of electrons is not evenly distributed across the wire. In the centre of the wire electrons propagate almost ballistically. However, when the electrons are forced into the boundaries of the wire diffusive scattering occurs. This is seen as a dramatic enhancement of the variance and characteristic period of the fluctuations at the field at which maximum boundary scattering is predicted. We compare our results with recent theories and construct an empirical model to describe the transport processes in the wire.1 Introduction Fluctuations of the conductance of phase-coherent, diffusive conductors have been studied for over two decades. The extraordinary phenomenon that these conductors exhibit is that, for the infinite variety of impurity configurations possible within them, the conductance never changes on average by more than e 2 /h from one configuration to another [1]. Consequently such fluctuations have been described as 'universal' in that they are independent of the physical parameters of the conductor. Interest in fluctuations has recently been renewed, by the question of true universality [2,3], and by the question concerning the applicability of the model to high-mobility systems [4,5]. In quantum wires the mechanism of fluctuations is rather complicated due to their small size and contribution of boundary scattering to the conductance. In the light of recent theories [4,5] that have attempted to address this question we perform experiments that demonstrate that the origin of the fluctuations change from quasi-ballistic to diffusive-like scattering when the electrons are forced into the wire boundary by a magnetic field.