SUPERCONDUCTORS WITH MESOSCOPIC PHASE-SEPARATION

A model of superconductivity is proposed taking into account repulsive particle interaction, mesoscopic phase separation and softening of th e crystalline lattice. These features are typical of many high-tempera ture superconductors. The main results obtained for the model are: (1) phase separation is possible only if repulsive forces play a signific ant role; (2) the critical temperature as a function of the supercondu cting phase fraction can have non-monotonic behaviour; (3) superconduc tivity is possible in heterophase systems even when it would be forbid den in pure samples. These results are in agreement with experiments.