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 superco nductor-normal metal-superconductor (SNS) junctions. Such junctions may exh ibit 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 cl ean systems and is stable against a bias voltage. Therefore, it is in princ iple possible to use these junctions as an active element in a variety of c ircuit applications such as oscillators, amplifiers or mixers, in the micro wave and millimeter-wave range.