Proposed model of a high-temperature excitonic superconductor

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Abstract
We present a detailed calculation of the transition temperature of a model filamentary excitonic superconductor. The proposed structure consists of a linear chain of transition-metal atoms to which is complexed a ligand system of highly polarizable dyelike molecules. Calculations of the electronic properties and experimental data on related materials are used to estimate the strength of the excitonic interaction, Coulomb repulsion, and band structure. From this the superconducting transition temperature was calculated by integration of the gap equation. For the particular structure proposed, transition temperatures of several hundred degrees are calculated. However, we find superconductivity only in those systems where the excitonic medium is within a covalent bond length of, and completely surrounds, the conductive spine. This imposes severe constraints on the structure of any excitonic superconductor. We show that for the structure proposed the momentum dependence of the exciton interaction results in the superconducting state being favored over the Peierls state and in vertex corrections to the electron-exciton interaction which are small.