Berlin 2024 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 18: Superconductivity: Poster
TT 18.3: Poster
Monday, March 18, 2024, 15:00–18:00, Poster C
Broadband microwave measurements on superconducting granular aluminum — •Jan Pusskeiler, Aniruddha Deshpande, Martin Dressel, and Marc Scheffler — 1. Physikalisches Institut, Universität Stuttgart, Stuttgart, Germany
Granular aluminum is an interesting superconductor because its critical temperature Tc can be changed by tuning the grain decoupling, measured by the normal-state resistivity. The resulting phase diagram contains a dome-shaped superconducting phase originating from the increasing superconducting energy gap Δ for weaker coupling of the grains. Decoupling on the other hand also suppresses the superfluid stiffness J due to phase fluctuations of the superfluid condensate. Hence, on the high resistivity side of the dome J < Δ and the superfluid density limits Tc [1]. The height of the superconducting dome (maximum Tc) is determined by the grain size, which can be reduced by cryogenic cooling of the substrate during sample fabrication.
We perform broadband microwave measurements in Corbino reflection geometry in the frequency range from 100 kHz to 20 GHz at temperatures down to 1.15 K. We investigate granular aluminum thin films that are grown at different substrate temperatures and that cover different parts of the superconducting dome. We determine their impedance, which gives access to the complex conductivity. We can thus observe how the superfluid density decreases with increased grain decoupling. Furthermore, we observe absorption features that we interpret as signatures of plasmonic modes of the superfluid condensate.
[1] U. S. Pracht et al., Phys. Rev. B 93 (2016) 100503(R)
Keywords: granular aluminum; broadband microwave spectroscopy; Corbino reflectometry; high kinetic inductance superconductors