Electronic structure of the high T sub c superconductor Ba sub 2 YCu sub 3 O sub (6.9).

The electronic structure of Ba sub 2 YCu sub 3 O sub (6.9) has been calculated using the linear augmented-plane-wave method. The results show strongly 2-dimensional and 1-dimensional features in the energy bands. These give rise to competing charge density wave instabilities. We argue that the proximity of these instabilities and the large electron-phonon matrix elements of the Fermi- level electrons make important contributions to the high T sub c of this material.