VAN-DER-WAALS ATTRACTION BETWEEN VORTICES IN HTSC

In anisotropic/layered superconductors the interaction between vortex segments directed along the ab-planes is of longer range than that bet ween the segments directed along the c-axis. This is a consequence of the anisotropic screening properties, with currents flowing along the c-axis being screened on the scale lambda/epsilon, whereas the current s flowing along the al-plane involve the planar Londen length lambda ( epsilon(2) = m/M much less than 1 denotes the anisotropy parameter). W e show that, as a result of these anisotropic screening properties, th ermal fluctuations of the flux-lines produce an attractive ''van der W aals''-type potential V-vdW between the vortices.