THERMODYNAMIC AND ELECTROMAGNETIC PROPERTIES OF HARD-CORE CHARGED BOSONS ON A LATTICE

We study thermodynamic and electromagnetic properties of the local ele ctron pair system being equivalent to that of hard-core charged bosons on a lattice. The theory of the response kernel is given and static e lectromagnetic properties of the model are analyzed in the superfluid phase in the random-phase approximation. The effects of quantum fluctu ations on the superfluid density are analyzed in detail for cubic latt ices. A generic feature of the London penetration depths ratio [lambda (0)/lambda(T)](2) in the considered system is the T-4 behavior in the T --> 0 limit and the 3D XY critical point behavior near T-c (for the screened long-range intersite interaction). In the low-density limit, a consistent description of superfluid characteristics is obtained wit h the use of the exact scattering length. The effects of long-range Co ulomb interaction on the excitation spectrum and finite temperature pr operties of the superconducting phase are also discussed. Finally, we briefly comment on the relevance of our results to the recent experime ntal data concerning the London penetration depth and the universal cr itical behavior in high T-c superconductors.