Band structure, insulator-metal transition and superconducting characteristics of two-dimensional BEDT-TTF-based systems

Metallic and semiconducting states of layered organic materials such as kap pa-ET2X salts are analyzed on the basis of bis(ethylenedithio)tetrathiafulv alene molecule (BEDT-TTF, hereafter ET) with essential intraET correlations of electrons. The insulator-metal phase transition of the Mott-Hubbard kin d is derived in agreement with available experimental data. Taking into acc ount the Fermi-surface topology the d-wave symmetry of superconducting orde r parameter is concluded and superconducting phase characteristics are calc ulated. The obtained value of 2 Delta(0)/T-c exceeds the BCS one. The resul ts are in agreement with measured nonactivated temperature dependencies of superconducting specific heat and NMR-relaxation rate of central carbons C- 13 in ET. (C) 1999 Elsevier Science B.V. All rights reserved.