Proximity effect and multiple Andreev reflections in gold atomic contacts

The transport properties of gold tunnel and few-atom clusters with superconducting leads were studied. From the analysis of the current-voltage characteristics in the framework of the diffusive proximity effect, the quasiparticle density of states at the contact region and the corresponding Andreev reflection amplitude was extracted. Following this, the multiple Andreev reflection (MAR) was extended to the case of a channel with arbitrary transmission between proximity effect (PE) superconductors. Results lead to the conclusion that the smallest gold contacts accommodate a single conduction channel in accordance with theoretical predictions for single-atom contacts.