Local structural excitations in the new superconducting oxides

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Abstract
The local structural excitations (LSEs) in the new superconducting oxides, based on the migration of the oxygen atoms in the Cu-O planes, are analysed with a simple microscopic model which involves two different local configurations and the transitions between them. A new electronic pairing mechanism via exchange of LSEs is suggested. By taking into account both the electron-phonon and the electron-LSE interactions, a formula for Tc in the strong-coupling case is derived. The results give a new insight into the relation between the oxygen vacancy structure and the superconducting transition temperature in these materials. It is shown that the orthorhombic structure with an ordered distribution of oxygen vacancies is more favourable for high Tc than is the tetragonal structure with disordered oxygen vacancies; for superconductors with a dominant LSE mechanism the isotopic effect is not easily observed under ordinary conditions. These arguments are in qualitative agreement with the current experimental results. Methods for obtaining further experimental confirmation of this are suggested.