title: What is measured in the scanning gate microscopy of a quantum point contact?
abstract: The conductance change due to a local perturbation in a phase-coherent nanostructure is calculated. The general expressions to first and second order in the perturbation are applied to the scanning gate microscopy of a two-dimensional electron gas containing a quantum point contact. The first-order correction depends on two scattering states with electrons incoming from opposite leads and is suppressed on a conductance plateau; it is significant in the step regions. On the plateaus, the dominant second-order term likewise depends on scattering states incoming from both sides. It is always negative, exhibits fringes, and has a spatial decay consistent with experiments.
authors.affiliation: Institut de Physique et Chimie des Matériaux de Strasbourg, UMR 7504, CNRS-UdS, 23 rue du Loess, B.P. 43, 67034 Strasbourg Cedex 2, France.
authors.forename: Rodolfo A
authors.initials: RA
authors.lastname: Jalabert
authors.forename: Wojciech
authors.initials: W
authors.lastname: Szewc
authors.forename: Steven
authors.initials: S
authors.lastname: Tomsovic
authors.forename: Dietmar
authors.initials: D
authors.lastname: Weinmann