ELECTRONIC-STRUCTURE AND ELECTRON-PHONON COUPLING IN HIGH-TC SUPERCONDUCTORS

The electronic structures for some high-T(c) compounds are calculated and anlyzed in terms of the Fermi surface and superconductivity. Calculated positron annihilation spectra are compared with experimental data in order to establish the possible Fermi surface structures. Various contributions to the electron-phonon coupling are calculated. It is found that some Ba modes and some high-frequency oxygen phonons have a considerable coupling via large Madelung shifts. The main reasons are the two-dimensionality, pure density of states and high ionicity. Results from model calculations show that many essential high-T(c) features can be consistent with large coupling to rapid phonon movements.