Divergence at low bias and down-mixing of the current noise in a diffusive superconductor-normal metal-superconductor junction

Understand

We present current noise measurements in a long diffusive superconductor-normal-metal-superconductor junction in the low voltage regime, in which transport can be partially described in terms of coherent multiple Andreev reflections.

• We show that, when decreasing voltage, the current noise exhibits a strong divergence together with a broad peak.
• We ascribe this peak to the mixing between the ac- Josephson current and the noise of the junction itself.
• We show that the junction noise corresponds to the thermal noise of a nonlinear resistor 4kBT=R with R V = I V and no adjustable parameters.