Jumps in electronic conductance due to mechanical instabilities

Using an exact single-particle scattering formalism we have carried out the first calculation of the conductance of a metallic contact, on the basis of a full dynamic simulation of the evolution of its atomic structure. We find that the contact area evolves discontinuously through a series of mechanical instabilities, which is reflected in a stepwise variation of the conductance also seen in recent experiments. Importantly, we find that the conductance is not simply proportional to the size of the contact and, therefore, the conductance per atom is not constant.