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Experimental evidence for counter current flow in superconductor-superconductor bilayers

Sep 22, 2022, 1:55 PM
30m
CEBAF Center auditorium

CEBAF Center auditorium

Beyond Nb: Alternate materials and mulilayer structures SRF Thin Film Characterization

Speaker

Md Asaduzzaman (University of Victoria, BC, Canada)

Description

We report evidence for counter current flow in superconductor-superconductor (SS) bilayers from depth-resolved measurements of their Meissner screening profiles using the low energy muon spin rotation (LE-$\mu$SR) technique. In these experiments, the implantation depth of the muons can be tuned/adjusted/controlled between ${\sim 10}$ nm and $\sim 150$ nm, below the surface, wherein their spin-precession reveals the field distribution inside the material (communicated via their radioactive decay products). Here we studied two prototypical SS bilayers [Nb-Ti-N(50 nm)/Nb and Nb-Ti-N(80 nm)/Nb] and compared the Meissner screening profiles obtained from LE-$\mu$SR against Kubo's counter current flow model, as well a naive (bi)exponential model. From fits to Kubo's model, we obtain a magnetic penetration depth for the thin Nb-Ti-N layers of $\lambda_\mathrm{Nb-Ti-N} = ({201 \pm 4})$ nm, in good agreement with literature values. In contrast, a naive exponential model overestimates the $\lambda_\mathrm{Nb-Ti-N}$ value by a factor of two, suggesting that it is inappropriate for quantifying $\lambda_\mathrm{Nb-Ti-N}$ in the SS bilayer. This also indicates that the surface current is suppressed by the counter current flow in the bottom superconductor. Our result suggests that SS bilayers are a viable means of overcoming the theoretical field limit of Nb.

Primary author

Md Asaduzzaman (University of Victoria, BC, Canada)

Co-authors

Dr Ryan M. L. McFadden (TRIUMF) Anne-Marie Valente-Feliciano (Jefferson Lab) Andreas Suter (Paul Scherrer Institute) Zaher Salman (Paul Scherrer Institute) Thomas Prokscha (Paul Scherrer Institute) Tobias Junginger (University of Victoria and TRIUMF)

Presentation materials