A COMPARATIVE THEORETICAL-ANALYSIS OF SUPERCONDUCTING ORGANIC CHARGE-TRANSFER SALTS AND HIGH-TC CUPRATES

The normal- and superconducting-state properties of organic charge transfer (CT) salts and high-Tc cuprates are compared. Fermi-surface (FS) nesting on nonplanar surfaces is possible in both classes of metals as a result of approximate particle-hole symmetry. The charge fluctuations 〈(Δn2i)〉 in the corresponding solids are described by the method of the local approach in the many-particle representation and the bond orbital approximation in the independent-particle scheme. The electronic configurations in the above systems allow for a coincidence of sizeable electronic correlations and large charge fluctuations which are even of extremal character. A simple strong coupling scheme is used to calculate the superconducting transition temperature Tc in organic superconductors and high-Tc cuprates. The estimated Tc values are of reliable accuracy. The different temperatures scales in the organic systems and the high-Tc cuprates are prevailingly determined by the Debye-temperature of the corresponding solids. A conventional mechanism of the BCS-type seems to be consistent with the experimental data. A possible violation of particle-hole symmetry for the stabilization of a superconducting ground state can be explained qualitatively. Electronic prerequisites supporting superconductivity in organic CT salts are summarized. © 1990.