Correlation effects in ET compounds

The ET salt family is described by a two parameter 2D Fermi surface model, in which bandwidth and departure from perfect nesting can be varied. We have studied the effect of spin fluctuations on the normal state properties in a RPA approach. The calculated NMR relaxation rate exhibits a peak in 1/T1T, which strongly decreases when the departure from perfect nesting of the Fermi surface and the bandwidth increase. These results are in perfect agreement with NMR experiments done in (BEDT-TTF)2 X (X= Cu[N(CN)2]Br, Cu(NCS)2), at least qualitatively. estigate the superconductivity pairing due to spin fluctuations and a model of quasi-2D electrons close to SDW instability, described by a two-parameter Fermi surface model, in which bandwidth and departure from perfect nesting can be varied. The coupling constants of various channels are calculated. They strongly depend on the nesting properties of the Fermi surface and on the bandwidth.