We have studied negative-resistance mixers both theoretically and experimentally. The current carried by the bound quasi-particles in the N-region of a mesoscopic SNS weak link has both DC and cosine components. Current transport in SNS weak links has been shown in many experiments to be affected by bias voltages. The I- V curves often show complex structures, including negative differential resistance which cannot be explained using the simple RSJ model. Supercurrent is directly affected by both the bias voltage and the density of states at the superconductor energy gap. The supercurrent as described by the Multip1e-Andreev-Reflection formula is varies markedly across subharmonic gap voltages because of the singularity of the density of state of superconductors near the energy gap. We have carried out mixer experiments on SNS weak links and have observed IF peaks at subgap voltages which are caused by the negative differential resistance.
展开▼
