Normal-state properties of BEDT-TTF compounds and the superconductivity pairing mechanism

The BEDT-TTF salt family is described by a two parameter two-dimensional (2 D) Fermi surface model, in which bandwidth and departure from perfect nesti ng can be varied. We have studied the spin fluctuation effects on the norma l-state properties in a random phase approximation approach. The calculated NMR relaxation rate exhibits a peak in 1/T1T, which strongly decreases whe n the departure from perfect nesting of the Fermi surface and the bandwidth increase. These results are in perfect agreement with Nh;LR experiments do ne in (BEDT-TTF)X (X = Cu[N(CN)](2)Br, Cu(NCS)(2)). We investigate the supe rconductivity pairing due to spin fluctuations and the same theoretical mod el of quasi-2D electrons close to the spin density wave instability. The co upling constants of various channels are calculated. They strongly depend o n the nesting properties of the Fermi surface and on the bandwidth.