Nonlinearity of transparent SNS weak links decreases sharply with length

Kavli Affiliate: Anton R. Akhmerov

| First 5 Authors: Valla Fatemi, Pavel D. Kurilovich, Anton R. Akhmerov, Bernard van Heck,

| Summary:

Superconductor-normal material-superconductor (SNS) junctions are being
integrated into microwave circuits for fundamental and applied research goals.
The short junction limit is a common simplifying assumption for experiments
with SNS junctions, but this limit constrains how small the nonlinearity of the
microwave circuit can be. Here, we show that a finite length of the weak link
strongly suppresses the nonlinearity compared to its zero-length limit — the
suppression can be up to a factor of ten even when the length remains shorter
than the induced coherence length. We tie this behavior to the nonanalytic
dependence of nonlinearity on length, which the critical current does not
exhibit. Further, we identify additional experimentally observable consequences
of nonzero length, and we conjecture that anharmonicity is bounded between zero
and a maximally negative value for any non-interacting Josephson junction in
the presence of time-reversal symmetry. We promote SNS junction length as a
useful parameter for designing weakly nonlinear microwave circuits.

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