Electrical transport properties of stable single-atom contacts of zinc

We report low-temperature measurements of the electrical transport properties of few-atom contacts of the superconducting metal zinc, arranged with lithographically fabricated mechanically controllable breakjunctions (MCB). The conductance histogram shows several narrow peaks, not regularly observed for multivalent metals. The first peak - corresponding to the single-atom contact - is located slightly below one conductance quantum and is split into two subpeaks, possibly indicating two preferred configurations of the single-atom contact. The current-voltage characteristics in the superconducting state show nonlinearities due to multiple Andreev reflections (MAR). In addition we find nonlinearities in the current-voltage characteristics that we attribute to electronic-interaction effects due to the granular structure of the film. Some of these latter findings are in qualitative agreement with a prediction by Avishai et al. A. Avishai, A. Golub, A. D. Zaikin, Europhys. Lett. {\bf 54}, 640.