The electromagnetic response of the CuO2-planes is calculated within a strong
coupling theory using model tight binding bands and momentum dependent pairing
interactions representing spin fluctuations and phonon exchange. The
superconducting state resulting from these interactions has d-wave symmetry.
With phonon exchange included the order parameter amplitude grows rapidly below
Tc at elevated frequencies which leads to improved agreement with the observed
temperature dependence of the penetration depth. Good agreement between theory
and experiment can only be achieved if it is assumed that the strength of the
quasiparticle interaction decreases with temperature in the superconducting
state. The amount of this reduction depends sensitively on the momentum
dependence of the interactions, the energy dispersion and the position of the
Fermi line.Comment: 3 pages, LaTex, to be published in J.Phys.Chem.Solids, 1997, SNS
Conf., Cape Co