Quantum interference effects in a system of two tunnel point-contacts in the presence of single scatterer: simulation of a double-tip STM experiment

The conductance of systems containing two tunnel point-contacts and a single subsurface scatterer is investigated theoretically. The problem is solved in the approximation of s-wave scattering giving analytical expressions for the wave functions and for the conductance of the system. Conductance oscillations resulting from the interference of electron waves passing through different contacts and their interference with the waves scattered by the defect are analyzed. The prospect for determining the depth of the impurity below the metal surface by using the dependence of the conductance as a function of the distance between the contacts is discussed. It is shown that the application of an external magnetic field results in Aharonov-Bohm type oscillations in the conductance, the period of which allows detection of the depth of the defect in a double tip STM experiment.Comment: 11 pages, 4 figures, to be published in Fiz. Nizk. Temp. (Low Temp. Phys.), V.37, No.1 (2011) corrected figure

Conductance of a STM contact on the surface of a thin film

The conductance of a contact, having a radius smaller than the Fermi wave length, on the surface of a thin metal film is investigated theoretically. It is shown that quantization of the electron energy spectrum in the film leads to a step-like dependence of differential conductance G(V) as a function of applied bias eV. The distance between neighboring steps in eV equals the energy level spacing due to size quantization. We demonstrate that a study of G(V) for both signs of the voltage maps the spectrum of energy levels above and below Fermi surface in scanning tunneling experiments.Comment: 15 pages, 5 figure

Electron tunneling into surface states through an inhomogeneous barrier: Asymptotically exact solution of the problem, and STM theory

We have found an asymptotically exact solution of the Schrödinger equation for electrons tunneling into surface states through an inhomogeneous barrier of large amplitude. Assuming an elliptic dispersion law for the charge carriers the “standing wave” pattern in the conductance of the system resulting from the electron scattering by a single defect in the vicinity of the surface is analyzed