Soliton Excitations In Josephson Tunnel Junctions

A detailed numerical study of a sine-Gordon model of the Josephson tunnel junction is compared with experimental measurements on junctions with different L/λ J ratio. The soliton picture is found to apply well on both relative long (L/λ J = 6) and intermediate (L/λ J . = 2) junctions. We find good agreement for the current-voltage characteristics, power output, and for the shape and height of the zero field steps (ZFS). Two distinct modes of soliton oscillations are observed. (i) a bunched or congealed mode giving rise to the fundamental frequency f 1 on all ZFS's and (ii) a 'symmetric' mode which on the Nth ZFS yields the frequency Nf 1 . Coexistence of two adjacent frequencies is found on the 3rd ZFS of the longer junction (L/λ J = 6) in a narrow range of bias current as also found in the experiments. Small asymmetries in the experimental environment, a weak magnetic field, e.g., is introduced via the boundary conditions of our numerical model. This gives a junction response to variations in the applied bias current close to that observed experimentally.

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