TEMPERATURE-DEPENDENCE OF THE ELECTRONIC-STRUCTURE OF ALPHA-(BEDT-TTF)(2)MHG(SCN)(4) (M = NH4, K, RB)

By using the reported temperature dependence of the lattice constants for organic metals alpha-(BEDT-TTF)(2)MHg(SCN)(4) (M = NH4, K, Rb), wh ere BEDT-TTF is bis(ethylenedithio)tetrathia fulvalene, the temperatur e dependence of the transfer integrals have been calculated, In additi on the derivatives of each transfer integral with respect to each latt ice constant are calculated. The transfer integrals are sensitive to t he change of the lattice constants within the conducting sheet. The ga p between the open and closed orbits in the momentum space is principa lly generated by the difference of the transfer integrals, c1 and c2; the magnitude of the intrastack dimerization determines the separation between the open and closed orbits. Among the various salts, the NH4 salt shows an exceptionally large shrinkage of the lattice constant c, which gives rise to large c1 - c2, a large gap, and results in a comp aratively small cross section of the closed Fermi surface. (C) 1997 El sevier Science B.V.