ANOMALOUSLY STRONG SMALL-Q ELECTRON-PHONON COUPLING IN CUPRATES DUE TO DIELECTRICITY

We consider the role of the enormous ionic dielectric constant epsilon (0) approximate to 30-50 in the cuprates. The ionically-screened Thoma s-Fermi screening parameter (q) over tilde(TF) = [4 pi e(2)N(E-F)/epsi lon(0)](1/2) is extremely small, namely 0.2-0.3 Angstrom(-1). The elec t;on-phonon coupling constant I(q, omega) is found to be anomalously l arge for q approximate to (q) over tilde(TF) and small omega, accounti ng for the CDW observed in overdoped BSCCO with wavevector 0.24 Angstr om(-1). Using the Eliashberg theory we derive from this I(q, omega) a maximum T-c of abcut 200 K. The small electron-phonon scattering angle Delta Theta = (q) over tilde(TF)k(F approximate to 0.3) rad acounts f or the observed d-wave pairing, as originating from a phonon-mediated mechananism.