Why shot noise does not generally detect pairing in mesoscopic superconducting tunnel junctions

The shot noise in tunneling experiments reflects the Poissonian nature of the tunneling process. The shot noise power is proportional to both the magnitude of the current and the effective charge q of the carrier. This can be used to detect electron pairing in superconductors[1, 2]. Here, I will present our results that shot noise can be controlled by the transparency in superconducting tunnel junctions [3]. Remarkably, we find that shot noise corresponds q=1e noise and thus does not reflect pairing in typical superconducting mesoscopic tunneling devices. We find that this is a consequence of the typical geometries of mesoscopic junctions. I will outline the potential for measuring shot noise in unconventional superconductors, and how we can tune transparency though the crossover from 1e to 2e-noise.

[1] K. M. Bastiaans et al., Direct Evidence for Cooper Pairing without a Spectral Gap in a Disordered Superconductor above Tc, Science 374, (2021).

[2] Y. M. Blanter and M. Büttiker, Shot Noise in Mesoscopic Conductors, Phys Rep 336, 1 (2000).

[3] J. Niu et al. Why shot noise does not generally detect pairing in mesoscopic superconducting tunnel junctions, arXiv:2306.02397, (2023).