Superconductivity and density wave in the quasi-one-dimensional systems: Renormalization group study

The anisotropic superconductivity and the density wave in the quasi-one-dimensional (q1d) system have been studied for a model with interactions of both the backward (g(1)) and the forward (g(2)) scatterings. By using the one-loop approximation in the Kadanoff-Wilson renormalization group method, it is found that the dependence of response functions on the temperature (T) is proportional to exp(1/T). The phase diagram for the q1d system is obtained on the g(2)-g(1) plane, where the noticeable change compared with the purely one-dimensional one appears in the superconducting state. The large charge fluctuation, which is induced by next-nearest neighbor interactions (V-2), suppresses the d(x2-y2) wave singlet superconducting (dSS) state but enhances the f-wave triplet superconducting (fTS) state. The field-induced f-wave triplet pairing could be expected for large V-2 since the transition temperature of fTS becomes comparable to that of AS. These features are discussed to comprehend the experiments on the (TMTSF)(2)PF6 salt.