Regensburg 2022 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 32: Focus Session: Topological Devices (joint session TT/KFM)

TT 32.4: Invited Talk

Thursday, September 8, 2022, 16:45–17:15, H10

Universal fluctuations of the induced superconducting gap in an elemental nanowire — Lauriane Contamin, Lucas Jarjat, William Legrand, Audrey Cottet, Takis Kontos, and •Matthieu Delbecq — Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université Paris-Diderot, Sorbonne Paris Cité, Paris, France.

Proximity induced superconductivity in a normal conductor is a rich field of experimental and theoretical investigations. Lately it has been at the heart of the quest for realizing topological modes in hybrid superconductor-nanowire nanodevices. Yet it turns out that there was a lack of investigations in elemental systems. In this work we therefore investigate an ultra-clean carbon nanotube coupled to a superconducting lead. We observe for the first time a long standing prediction of random matrix theory (RMT) that mesoscopic fluctuations of the mini-gap in a conductor follow a universal distribution with a clear transition when time reversal symmetry is broken, as predicted by RMT. Interestingly, mesoscopic fluctuations of the minigap were precisely predicted to lead to ubiquitous nontopological edge states clustering towards zero energy. We do indeed observe ubiquitous and robust zero bias conductance peaks under magnetic field in our device that cannot host topological modes by design. The RMT predictions that are compatible with our observations are very general and should be present in any system showing disorder. It therefore calls for alternatives to transport measurement to identify Majorana modes in 1D systems with microwave photons in a cavity as a promising platform.