On the interaction of holes with apical oxygen vibrations in the high-Tc cuprates

Abstract We present results for a very simple model for the interaction of holes and apical oxygen vibrations in high- T c cuprates, and discuss related models which have been applied to the same problem. We find that the existence of two oxygen positions is a common feature — in the appropriate parameter range — of these models. In this range the adiabatic approximation fails; besides, the solutions become unstable with respect to very small asymmetrization of the systems, which results in doping and temperature dependent physical properties.