Negative differential resistance at atomic contacts

Negative differential resistance is found for a pair of electrodes each consisting of a single Al atom coupled to a flat metal surface, where the Al atom is separated from the surface by a "spacer" atom (Br). This behavior is seen when the Al atoms are at a short distance from one another, and disappears when the distance is decreased to the point at which the Al atoms are in contact. © 1997 The American Physical Society.