Elementary pinning force for a superconducting vortex

The elementary pinning force ${\mathrm{f}}_{\mathrm{p}}$ has been measured for a single vortex trapped in one of the superconducting layers of a cross-strip Josephson junction. At temperatures close to the transition temperature the vortex can be pushed across the junction by a transport current. The vortex is found to move in a small number of discrete steps before it exits the junction. The pinning force for each site is found to be asymmetric and to have a value of about ${10}^{\mathrm{-}6}$ N/m at the reduced temperature, t=T/${\mathrm{T}}_{\mathrm{c}}$=0.95. As a function of temperature, ${\mathrm{f}}_{\mathrm{p}}$ is found to vary approximately as (1-t${)}^{3/2}$. .AE