ELECTRON-TUNNELING THROUGH A BCS SUPERCONDUCTOR WITH AN UNPAIRED ELECTRON

We calculate the second-order above gap tunneling current of a mesosco pic double junction system. The middle island is a BCS superconductor, which might contain an even or odd number of electrons. In the case o f odd number parity, there is an unpaired electron in the superconduct ing island. We study the effect of this unpaired electron on the tunne ling current through modification to the BCS Green's function. It is f ound that the tunneling current decreases because of this unpaired ele ctron. Within a certain range of parameters, this second-order current is the preponderant contribution to the I-V characteristic of the dou ble junction and therefore should be measurable.