RELATION BETWEEN THE CU(1)-O(4) DISTANCE AND T(C) IN Y1-2XCAXTHXBA2CU3O7-DELTA - RAMAN-SCATTERING AND CALCULATION OF THE ELECTRON-PHONON INTERACTION

The strong depression of T(c) with Ca-Th substitution in Y1-2xCaxThxBa2Cu3O7-delta has been investigated in a model calculation of the electronic and phononic contributions from the apex oxygen, O(4), on the electron-phonon interaction, lambda. The shift with Ca-Th substitution of the characteristic O(4) vibrational mode was measured by Raman scattering. The electronic part eta of lambda has been calculated at several distances between chain Cu(1) and O(4) in the region of the observed variation with x. Eta was found to depend strongly on this distance. The results show a small increase with x of the O(4) frequency and a strong decrease of eta. Both these factors thus contribute to a decrease of lambda. We therefore find evidence that a decreasing electron-phonon interaction is associated with the depression of T(c) in Ca-Th substituted YBa2Cu3O7-delta.