Observation of Cylindrical Cavity Modes in Circular Josephson Weak-Link Junctions

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Abstract
We report the observation of self‐induced step structure in the I‐V characteristic of bulk‐Hg/C/Sn multiple weak‐link Josephson junctions formed by freezing a small drop of mercury onto the surface of a carbon covered tin film. The voltages at which steps appear are found to correspond to the frequencies of the resonant modes of the open‐sided cylindrical rf cavity formed by the circular bottom of the mercury drop and the tin film. The effect of temperature and applied magnetic field on the junction critical current and on the step behavior is explored. The observation of such cylindrical cavity modes is contrasted with the situation for rectangular Josephson junctions where only the ``strip‐line'' resonances have been observed.