Theoretical studies of possible excitonic superconducting state in CuCl and CdS

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Abstract
To explain the observed diamagnetic anomalies which are coupled with high conductivity in CuCl and CdS samples, an excitonic mechanism of superconductivity based on the presence of impurities is outlined. To formulate the theoretical model on a more fundamental level, four-component field operators have been introduced in analogy to the Nambu formalism. Generalized Eliashberg equations for the self-energy are derived for both singlet and triplet pairs. Numerical model calculations for the effective interaction are presented for different impurity concentrations and different gaps (exciton frequencies). Conjectures for the further development of the theory, together with proposed experiments, conclude this study.