Mesoscopic SNS mixers using negative resistance at low voltage

Abstract

The current carried by the bound quasi-particles in the N-region of a mesoscopic superconductor-normal-metal-superconductor (SNS) weak-link has dc and cosine components. The dc component depends on the pair charge (-2e) transferred by each Andreev reflection at an NS interface. The pair-charge transfers decrease due to reduction of the allowed number of Andreev reflections when the voltage increases. This is the origin of the negative differential resistance at low bias voltage observed in I-V curves of SNS junctions. The quasi-particle states carrying the supercurrent in the N-region can sensitively be influenced by external high-frequency fields. In an experiment of the mesoscopic SNS mixer, prominent IF signal peaks are observed at low bias voltage. Each IF signal peak appeared in the broad bias voltage region, which corresponds to the broadness of the negative differential resistance region at low bias voltage. The SNS mixer operation at low voltage is promising for application to low-noise mixers in submillimetre-wave region.