We have measured at low temperatures the current through a submicrometer superconducting island connected to nornal metal leads by ultrasmall tunnel junctions. At low bias voltages, the current changes from being e-periodic in the applied gate change to 2e-periodic. We interpret this 2e-periodic current as a manifestation of a sequence of Andreev reflection events which transports two electrons at a time across the island. This behavior is clear evidence that there is a difference in total energy between ground states of differing electron number parity.
Citation: Physica B-Condensed Matter
Issue: Part 1
Pub Type: Journals
Andreev reflection, Coulomb blockade, general superconductivity, ultra-small tunnel junctions