Optic breathing mode, resonant charge fluctuations, and high-Tc superconductivity in the layered perovskites

Frozen-phonon optical breathing mode calclations on La2-xMxCuO4 (M=Ba,Sr,...) demonstrate the following: (i) a large (3 eV/A) electron-phonon interaction matrix element for the &O px,y orbitals, (ii) a high frequency (110 meV), and (iii) large charge fluctuations (0.3 electrons). Especially significant is the possible resonant coupling to, and enhancement of, the natural ground-state Cu2+-Cu3+ charge fluctuations between in-plane Cu atoms. The relation of these results to the high Tc (and previous theoretical descriptions of superconductivity) is indicated.