Parity Effects on Electron Tunneling through Small Superconducting Islands

Abstract

Single electron tunneling into small superconducting islands is sensitive to the gap energy of the excitations created in the process and, hence, depends on the electron number parity. At low temperature the properties of the system are 2e-periodic in the applied gate voltage, turning e-periodic at higher temperature. We evaluate the tunneling rates and determine the probabilities for the even and odd state as well as the cross-over condition from the balance between different processes. Our analysis includes excitations in the leads. They are essential if the leads are superconducting. The influence of parity effects on single electron tunneling, Cooper pair tunneling, and the Andreev reflection in superconducting transistors yields rich structures in the I-V characteristic, which explains recent experimental findings.