Superconductor-normal metal-superconductor junctions for signal amplification and harmonic multiplication

We report signal amplification and harmonic multiplication processes based on the nonlinear current-voltage characteristics (CVC) displayed by superconductor-normal metal-superconductor (SNS) junctions. Such junctions may exhibit a negative differential resistance at low voltages, the so called low-voltage-negative-differential-resistance (LVNDR) effect. This effect is due to the quantum mechanical multiple Andreev reflection mechanism in very clean systems and is stable against a bias voltage. Therefore, it is in principle possible to use these junctions as an active element in a variety of circuit applications such as oscillators, amplifiers or mixers, in the microwave and millimeter-wave range.