Static and dynamic transport in parity-sensitive systems

Abstract

A microscopic theory has been constructed to investigate tunneling current and shot noise in a normal-superconductor-normal (NSN) single-electron transistor (SET). In contrast to the time-averaged current, the time-dependent current that determines the shot noise depends on where in the circuit it is measured. For an even-parity superconducting ground state the pair-tunneling in the dominating Andreev channel will be suppressed as one or both of two single-particle channels open up at increased bias voltages. With further increase of bias, Andreev tunneling between odd-parity charge states contributes significantly to the current. Threshold voltages for these tunneling processes vary with circuit parameters and can be identified with the normalized shot noise, which is more sensitive to both the switching of charge transport channels and the circuit parameters of the NSN SET than the time-averaged current. Our calculated results have been compared with recent experiments.