VAN-DER-WAALS INTERACTION BETWEEN FLUX LINES IN HIGH-T-C SUPERCONDUCTORS

In anisotropic or layered superconductors thermal fluctuations as well as impurities induce a van der Waals (vdW) attraction between flux li nes, as has recently been shown by Blatter and Geshkenbein in the ther mal case [6] and by Mukherji and Nattermann in the disorder dominated case [10]. This attraction together with the entropic or disorder indu ced repulsion has interesting consequences for the low held phase diag ram. We present two derivations of the vdW attraction, one of which is based on an intuitive picture, the other one following from a systema tic expansion of the free energy of two interacting flux lines. Both t he thermal and the disorder dominated case are considered. In the ther mal vase in the absence of disorder, we use scaling arguments as well as a functional renormalization of the vortex-vortex interaction energ y to calculate the effective Gibbs free energy on the scale of the mea n flux line distance. We discuss the resulting low field phase diagram and make quantitative predictions for pure BiSCCO (Bi2Sr2CaCu2O8). In the case with impurities, the Gibbs free energy is calculated on the basis of scaling arguments, allowing for a semi-quantitative discussio n of the low-field, low-temperature phase diagram in the presence of i mpurities.