Electrical transport through a molecular nanojunction

We consider electrical transport through a system of a molecule coupled to metallic electrodes. We give an overview of some of the issues involved in the problem. We discuss the two extreme regimes of transport. In the strong molecule-electrode coupling limit interaction effects beyond the Hartree-Fock level can be ignored. The transport can be described by a single particle scattering or Landauer approach. In the weak-coupling limit interaction effects dominate and the molecule must be treated as a many-body system. The transport is best described by incoherent sequential tunneling of single electrons. We discuss in general terms the relevance of spatial electronic structure, field effects and relaxation on the molecule. As an example, we consider a simple model for a molecule in the weak coupling limit. The model includes charging effects as well as aspects of the electronic structure of the molecule. The interplay of strong interactions and an asymmetry of the metal-molecule coupling can lead to various effects in non-linear electrical transport. In particular, strong negative differential conductance is observed under rather generic conditions.