Vortex Motion and Vortex Friction Coefficient in Triangular Josephson Junction Arrays
Abstract
The dynamical response of triangular JJA is investigated using the RCSJ model. A flux flow regime is found to extend between a lower vortexdepinning current and a higher critical current, in agreement with previous calculations for square arrays. In the flux flow regime, the dynamical response to the bias current is roughly Ohmic, and the timedependent voltage can be well understood in terms of vortex degrees of freedom. The vortex friction coefficient $\eta$ depends strongly on the McCumberStewart parameter $\beta$, and at large $\beta$ is approximately independent of the shunt resistance $R$. To account for this, we generalize a model of Geigenmüller {\it et al} to treat energy loss from moving vortices to the phase analog of optical spin waves in a triangular lattice. The value of $\eta$ at all values of $\beta$ agrees quite well with this model in the lowdensity limit. The vortex depinning current is estimated as $0.042I_c$, independent of the direction of applied current, in agreement with static calculations by Lobb {\it et al}. A simple argument suggests that quantum effects in vortex motion may become important when the flux flow resistivity is of order $h/(2e)^2$ per unit frustration.
 Publication:

arXiv eprints
 Pub Date:
 December 1993
 arXiv:
 arXiv:condmat/9312047
 Bibcode:
 1993cond.mat.12047W
 Keywords:

 Condensed Matter
 EPrint:
 12 pages + 14 figures, REVTeX 3.0, will be published in Phys. Rev. B