The properties of high-T^c superconducting materials that relate to characteristics of marginal ferroelectrics: Internal perturbation local field calculations and relationship to mechanism

Abstract

High-T^c superconducting oxides are composed of structural elementary building blocks including pyramids, planes, and chains in such a manner so as to create a large internal local electric perturbation field. In addition, the presence of d⁹ Cu²⁺ creates a Jahn-Teller distortion affecting the position of the of apical oxygen (04) ions. Observations have also been reported of spontaneous polarization, piezoelectricity, pyroelectricity, and circular dichroism in this class of materials. These structural and property criteria suggest that high-T_c Perovskite-like superconductors in their normal state may be in the microscopic domain a special case of marginal ferroelectric materials. The importance of ferroelectric polarization in the pre-transition normal state relates to a number of phenomena which are reported to be associated with the high-T_c mechanism such as phonons, polarons, and charge transfer excitations. The unique structure of the Y₁Ba₂Cu₃O_7-a gives rise to local perturbation electric fields which are calculated by a multicell point charge computer code herein described. The resonant charge transfer excitation establishes a virtual exciton which creates electron-electron coupling in the form of Cooper pairs.