Past QuMat seminars in Utrecht

The QuMat seminars in Utrecht is a bi-weekly joint venture between Utrecht’s experimental and theoretical condensed matter physics groups.
Coming QuMat seminars are listed here.

Videos from previous talks are available on youtube and listed here.

Electron pairs without superconductivity

Speaker: Milan Allan – Leiden University

Host: Ingmar Swart



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)

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