Elementary pinning force for a superconducting vortex

The elementary pinning force fₚ 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^-6 N/m at the reduced temperature, t=T/Tc=0.95. As a function of temperature, fₚ is found to vary approximately as (1-t)3/2. .AE