Quantum transport in an atom-sized bridge between a metal surface and a tip of a scanning tunneling microscope at finite temperatures

Electron transport in an atom-sized bridge between a metal surface and a ti p of a scanning tunneling microscope is investigated with the aid of the Hu bbard Hamiltonian laying stress on the effects of the intrasite Coulomb int eraction. The second-order self-energy with respect to the Coulomb interact ion in a single-site approximation is taken into account in calculating the conductance of the bridge. On the basis of the calculation, we closely exa mine the effects of the Coulomb interaction on the conductance as a functio n of the stretching length of the bridge. We show that the conductance valu e at the plateau deviates from multiples of the universal value of 2e(2)/h, and that the deviation increases as the temperature is decreased. This tem perature dependence increases with the strength of the Coulomb interaction. In addition, when the subband edge lies energetically near the Fermi energ y, a valley appears between the plateaus. When the Coulomb interaction is w eak at a high temperature, or when the Coulomb interaction is strong at a l ow temperature, the valley becomes a quasiplateau. (C) 1999 American Instit ute of Physics. [S0021-8979(99)03602-6].