Quasiparticle Characteristics and Noise Properties of Superconductor-Normal Metal-Superconductor Quantum Well Devices.

All-thin film superconducting Nb-Nb nanoconstriction-NbN quantum well devices with improved low-frequency noise properties have been successfully fabricated. The quasiparticle current characteristics of this device are well explained by the Andreev reflection current. The low-frequency noise parameter η in Hooge's empirical theory decreases quickly with increasing device quality factor Q eff = R D (1 mV)/R N (10 mV), i.e., with decreasing effective strength of the barrier potential at the superconductor (Nb, or NbM-nanoconstriction interface