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

We present current noise measurements in a long diffusive superconductor-normal-superconductor junction, in the temperature range for which current-voltage characteristics are reversible. We focus on 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 Josephson current beating and the noise of the junction itself. At high temperature, we show that the junction noise corresponds to the thermal noise of a non linear resistor $4k_BT/R$ with $R=V/I(V)$ and no adjustable parameters.