Imaging coherent electron flow in a two-dimensional electron gas

Images of coherent electron flow through a two-dimensional electron gas in a GaAs/AlGaAs heterostructure from a quantum point contact (QPC) were obtained at liquid He temperatures by using a scanning probe microscope with a charged tip that backscatters electrons. Near the QPC, at distances less than View the MathML source, the images show angular lobes of electron flow in patterns determined by the quantum modes of the QPC. At greater distances, narrow branches of electron flow are observed, formed by the cumulative effects of small-angle scattering. In addition, the images show fringes spaced by half the Fermi wavelength, evidence that the electron flow is coherent. These observations agree well with theoretical simulations of electron flow.