Low-voltage negative-resistance mixers of nano-meter SNS junctions

The current carried by the bound quasi-particles in the N region of a mesoscopic SNS junction has dc and cosine components. The dc current component is carried by the pair charge (-2e) transferred by a couple of Andreev reflections at both of the NS interfaces. The pair-charge transfers decrease due to reduction of the allowed number, 2/spl Delta//V, of Andreev reflections when the voltage, V, increases. Therefore, the low-voltage negative-differential-resistance is observed on the I-V curves of mesoscopic SNS junction, when the junction is driven by the low impedance voltage-bias source. The supercurrent carried by the quasi-particle in the N-region is sensitive to the external high-frequency fields. In a mixer experiment using the nano-meter SNS junctions of NbN, prominent IF signal peaks are observed at low bias voltage. Each IF signal peak corresponds to the negative differential resistance region at low bias voltage.