The oscillatory voltage dependence of the conductance of a quantum point contact in the presence of a single point-like defect was analyzed theoretically. Such signals could be exploited to obtain information on the defect positions below a metal surface. Both tunnel junctions and ballistic contacts of adiabatic shape were considered. The effect of quantum interference was taken into account between the principal wave that was directly transmitted through the contact and the partial wave that was scattered by the contact and the defect. This effect led to oscillations of the conductance as a function of the applied voltage. The dependence of the period and amplitude of the conductance oscillations upon the position of the defect within the metal was obtained.

Method to Determine Defect Positions Below a Metal Surface by STM. Y.S.Avotina, Y.A.Kolesnichenko, A.N.Omelyanchouk, A.F.Otte, J.M.van Ruitenbeek: Physical Review B, 2005, 71[11], 115430 (8pp)