SUPERCONDUCTIVITY WITH SOFT LATTICE MODES IN LaBaCuO and YBaCuO

Abstract

The canonical transformation employed in polaron theory at intermediate coupling is generalized to the electron phonon interaction of an entire band of electrons. Interelectron interactions result. The overall lattice-electron correlation is obtained with a variational calculation, balancing the extra elastic energy stored in the lattice against the negative energy arising from BCS pair correlation. The requisite phonon softening to attain any given value of Tc in metallic LaBaCuO and YBaCuO are estimated. The implicit fluctuations in the lattice normal coordinates are compared with results yielded by the EXAFS measurements of Oyanagi et al.