Electron pairs without superconductivity

Speaker: Milan Allan – Leiden University

Host: Ingmar Swart

Abstract:

The idea that preformed electron pairs could exist in a superconductor above its zero-resistance state has been explored for decades, yet direct experimental evidence is lacking. In this talk, I will introduce new instrumentation that can unambiguously and quantitatively detect electron pairs: the electron pair microscope [1-3]. Applying it to the disordered superconductor titanium nitride, we discover a state where almost all electrons are paired up to temperatures much higher than the critical temperature Tc, by observing a clear enhancement in the shot noise from an equivalent of 1 electron charge to an equivalent of 2 electron charges [4]. We further show that the spectroscopic gap fills up rather than closes when increasing temperature. Our results thus demonstrate the existence of a novel quantum state above Tc that, much like an ordinary metal, has no (pseudo)gap, but carries charge entirely via paired electrons.

[1] KM Bastiaans et al., RSI 89, 093709 (2018)
[2] KM Bastiaans, D. Cho et al., Nature Physics 14, 1183 (2018)
[3] KM Bastiaans et al., Phys. Rev. B 100, 104506 (2019)
[4] KM Bastiaans, et al. Science 374, 608 (2021)