Anomalously strong small-q electron-phonon coupling in cuprates due to dielectricity

Abstract

We consider the role of the enormous ionic dielectric constant e0≈ 30–50 in the cuprates. The ionically-screened Thomas-Fermi screening parameter ~qTF= [4θe2N(EF)/ein01/2 is extremely small, namely 0.2-0.3 A-1. The electron-phonon coupling constant I(q,w) is found to be anomalously large forq ≈ ~qTF and smallco, accounting for the CDW observed in overdoped BSCCO with wavevector 0.24 A-1. Using the Eliashberg theory we derive from this I(q,w) a maximumTc of about 200 K. The small electron-phonon scattering angle △θ = ~qF ≈0.3 rad acounts for the observedd-wave pairing, as originating from a phonon-mediated mechananism.