General properties of anisotropic superconductors with mesoscopic phase
separation are analysed. The main conclusions are as follows: Mesoscopic phase
separation can be thermodynamically stable only in the presence of repulsive
Coulomb interactions. Phase separation enables the appearance of
superconductivity in a heterophase sample even if it were impossible in
pure-phase matter. Phase separation is crucial for the occurrence of
superconductivity in bad conductors. Critical temperature for a mixture of
pairing symmetries is higher than the critical temperature related to any pure
gap-wave symmetry of this mixture. In bad conductors, the critical temperature
as a function of the superconductivity fraction has a bell shape. Phase
separation makes the single-particle energy dispersion softer. For planar
structures phase separation suppresses d-wave superconductivity and enhances
s-wave superconductivity. These features are in agreement with experiments for
cuprates.Comment: Revtex file, 25 pages, 2 figure