Abstract
The electrical resistivity in organic superconductors show the T^2-dependence at low temperatures above Tc. This fact suggests that the electron-electron interaction determines the damping of quasi-particle in the Fermi liquid state. In this paper, we calculate selfconsistently the temperature dependence of damping rate due to the electron-electron interaction. Then, using this damping rate, we calculate the temperature dependence of NMR relaxation rate, for the two cases with s and d-pairing states, respectively. Our result shows that, when the damping rate at Tc is of the same order as Tc, no coherence peak appears in T-1_1 even if the superconducting state possesses s-wave symmetry. However, we cannot eliminate a hump structure appearing at low temperatures, at which the s-wave gap begins to open against the damping effect. On the other hand, the relaxation rate for d-wave decreases smoothly. This is the important difference in determining the pairing symmetry. We discuss the comparison of our result with experimental data for several systems.
