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Multiple Andreev reflection in single atom niobium junctions

B. Ludoph·N. van der Post·E. N. Bratus'·E. V. Bezuglyi·V. S. Shumeiko·G. Wendin·J. M. van Ruitenbeek
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Abstract

Single atom junctions between superconducting niobium leads are produced using the Mechanically Controllable Break Junction technique. The current-voltage characteristics of these junctions are analysed using an exact formulation for a superconducting quantum point contact. For tunnelling between two single atoms with a sufficiently large vacuum barrier, it is found that a single channel dominates the current, and that the current-voltage characteristic is described by the theory, without adjustable parameters. For a contact of a single Nb atom it is shown that five conductance channels contribute to the conductance, in agreement with the number expected based on the number of valence orbitals for this d-metal. For each of the channels the transmission probability is obtained from the fits and the limits of accuracy for these numbers are discussed.

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B. Ludoph, N. van der Post, E. N. Bratus', E. V. Bezuglyi, V. S. Shumeiko, G. Wendin, J. M. van Ruitenbeek. 1999-08-16. Multiple Andreev reflection in single atom niobium junctions. https://doi.org/10.1103/physrevb.61.8561

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