Divergence at Low Bias and Down-Mixing of the Current Noise in a Diffusive Superconductor–Normal-Metal–Superconductor Junction

Abstract

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 non-linear resistor 4kBT /R with R = V /I(V ) and no adjustable parameters.

Thermal fluctuations and flux-tunable barrier in proximity Josephson junctions

“…These differences may explain the previously observed strong fluctuations in nanoscale proximity junctions, [4][5][6] which manifest themselves as "enhanced" broadening of the current-voltage characteristics (CVC) compared to the "intrinsic" broadening of CVC due to thermal activation of a resistively shunted junction (RSJ), as described by Ambegaokar and Halperin (AH). 7,8 This enhancement can be characterized by an effective noise temperature T N , which is higher than the bath temperature T b .…”

Possible Resonance Effect of Axionic Dark Matter in Josephson Junctions

“…In this letter we propose a new approach how to detect QCD-axionic dark matter in the laboratory with high efficiency, exploiting a macroscopic quantum effect. Our proposal is based on S/N/S (Superconductor/Normal Metal/Superconductor) Josephson junctions as suitable detectors [12][13][14][15][16]. We will provide theoretical arguments that axions that pass through the weak link region of such a Josephson junction in the voltage stage may trigger the transport of additional Cooper pairs if the Josephson frequency ω J coincides with the axion mass m a c 2 = ω J .…”

“…The measured differential conductance (see e.g. [12][13][14][15] for typical measurement techniques) is predicted to exhibit a small peak at Josephson frequency ω J = 2eV = m a c 2 , whose intensity depends on the velocity of galactic axions hitting the earth, the size of the weak-link region of the junction, and the local galactic halo density of axions.…”

Hybrid superconducting nanostructures: very low temperature local probing and noise

“…Therefore, additional noise sources must be involved. It is worth noting that this deviation from a pure quasiparticles noise occurs below 525 mK, which corresponds to k B T 3.5 E Th , very close to the mini-gap width (3.1 E Th ) [22]. This suggests that coherent processes, which become relevant in this energy scale, should play a role here.…”

“…In such a situation, the voltage fluctuations S(ω) at low frequency are determined not only by the current fluctuations at the frequency ω, but also by those close to the Josephson frequency ω J and its harmonics. Under some assumption [22], the low frequency noise can be written as…”