Thermal depinning of fluxons in discrete Josephson rings

J. J. Mazo; F. Naranjo; K. Segall

doi:10.1103/PhysRevB.78.174510

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Thermal depinning of fluxons in discrete Josephson rings

J. J. Mazo, F. Naranjo, K. Segall

DOI 10.1103/PhysRevB.78.174510 · Physical Review B

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Abstract

We study the thermal depinning of single fluxons in rings made of Josephson junctions. Due to thermal fluctuations a fluxon can be excited from its energy minima and move through the array, causing a voltage across each junction. We find that for the initial depinning, the fluxon behaves as a single particle and follows a Kramers-type escape law. However, under some conditions this single-particle description breaks down. At low values of the discreteness parameter and low values of the damping, the depinning rate is larger than what the single-particle result would suggest. In addition, for some values of the parameters the fluxon can undergo low-voltage diffusion before switching to the high-voltage whirling mode. This type of diffusion is similar to phase diffusion in a single junction but occurs without frequency-dependent damping. We study the switching to the whirling state as well.