Why Shot Noise Does Not Generally Detect Pairing in Mesoscopic Superconducting Tunnel Junctions

• Published in: Physical review letters Vol. 132; no. 7; p. 076001
• Main Authors: Niu, Jiasen, Bastiaans, Koen M, Ge, Jian-Feng, Tomar, Ruchi, Jesudasan, John, Raychaudhuri, Pratap, Karrer, Max, Kleiner, Reinhold, Koelle, Dieter, Barbier, Arnaud, Driessen, Eduard F C, Blanter, Yaroslav M, Allan, Milan P
• Format: Journal Article
• Language: English
• Published: United States 16.02.2024
• ISSN: 1079-7114
• DOI: 10.1103/PhysRevLett.132.076001

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 of the carrier. Shot-noise spectroscopy thus enables us, in principle, to determine the effective charge q of the charge carriers of that tunnel. This can be used to detect electron pairing in superconductors: In the normal state, the noise corresponds to single electron tunneling (q=1e), while in the paired state, the noise corresponds to q=2e. Here, we use a newly developed amplifier to reveal that in typical mesoscopic superconducting junctions, the shot noise does not reflect the signatures of pairing and instead stays at a level corresponding to q=1e. We show that transparency can control the shot noise, and this q=1e is due to the large number of tunneling channels with each having very low transparency. Our results indicate that in typical mesoscopic superconducting junctions, one should expect q=1e noise and lead to design guidelines for junctions that allow the detection of electron pairing.