Electron transport from a one- to a two-dimensional system: Scanning tunneling microscopy of an adatom on a metal surface

Abstract

Making use of the nonequilibrium Green function formalism, we theoretically study at length the problem of electron transport through a single central site, with a single energy level, which is connected to a one-dimensional (1D) atomic chain, or lead, and a quasi-two-dimensional (2D) electron gas. The system under question might be seen to be the simplest model to study an adatom on a metal surface in a scanning tunneling microscopy experiment. We attach particular importance to the bound state which appears at the energy, in the local density of states of the central site, slightly below the surface-state low band edge. The coupling between the central site and the 2D part is reconfirmed to be the origin of the bound state. It seems that the very existence of the bound state might be verified experimentally by detecting a small but significant variation in the current in a suitable interval of voltage bias, analogous to the conventional differential conductance analysis. It is also demonstrated that the 1D lead-adatom coupling, too, imposes substantial effects on the system.