ELECTRONIC STABILIZATION OF THE SUPERCONDUCTING COMPOSITION OF CUPRATE SUPERCONDUCTORS

By making analogies between the behavior with interatomic separation of the electronic states of small molecules such as the alkali halides with those of the cuprate superconductors, a model is generated which allows insights into the nature of the electronic description of the latter. Interaction between the state where the holes are carried on the oxygen atoms and the state where they are located on the copper atoms leads to a stabilization of the lower energy state. At critical values of the doping level and copper-oxygen distance, such a stabilization leads to a state which is a local thermodynamic minimum with mixed electronic character. It is shown how fluctuations in this state may be important, how it is very sensitive indeed to chemical composition, and how it can rationalize the thermodynamic stability of the superconducting composition. © 1992.