Atom oscillations in the scanning tunneling microscope

Time scales of the atomic oscillations between surface and tip in the scanning tunneling microscope (STM) are investigated by semiclassical methods and by the numerical integration of the time-dependent Schroedinger equation. It is shown that the upper limit of the time interval of stationary decay across the barrier is very small, and complete tunneling can be explained only by the resonance phenomenon of quantum coherence oscillations. The occurrence of these resonances at the variation of the bias voltage is studied for the first two isomeric states of a Xe atom in a sample-tip potential of double-well shape. The resonant bias voltages for these two states prove to coincide, and at the first common resonance the effect of temperature is discussed. The results provide a new frame for understanding the mechanism of atom transfer in STM. (author) 5 Figs., 10 Refs