This tutorial article presents a "bottom-up" view of electrical resistance starting from something really small, like a molecule, and then discussing the issues that arise as we move to bigger conductors. Remark ably enough, no serious quantum mechanics is needed to understand electrical conduction through something really small, except for unusual things like the Kondo effect that are seen only for a special range of parameters. This article starts with energy level diagrams (Section2), shows that the broadening that accompanies coupling limits the conductance to a maximum of q2/h per level (Sections 3, 4), describes how a change in the shape of the self-consistent potential profile can turn a symmetric current-voltage characteristic into a rectifying one (Sections 5, 6), shows that many interesting effects in molecular electronics can be understood in terms of a simple model (Section 7), introduces the non-equilibrium Green's function (NEGF) formalism as a sophisticated version of this simple model with ordinary numbers replaced by appropriate matrices (Section8) and ends with a personal view of unsolved problems in the field of nanoscale electron transport (Section9). Appendix A discusses the Coulomb blockade regime of transport, while Appendix B presents a formal derivation of the NEGF equations. MATLAB codes for numerical examples are listed in Appendix C and can be downloaded from www.nanohub.org, where they can also be run without installation.
Cite this work
Researchers should cite this work as follows:
- S. Datta, "Electrical resistance: an atomic view," Nanotechnology, 15, S433-S451 (2004).
- molecular electronics