We present a microscopic theory of fluctuation-mediated pairing mechanism in organic superconductors ${ (TMTSF)}_{ 2}X$, where the experimentally observed coexistence of $2k_{ F}$ charge fluctuation and $2k_{ F}$ spin fluctuation is naturally taken into account. We have studied, within the random phase approximation, the extended Hubbard model at quarter-filling on a quasi-one-dimensional lattice, where we consider the off-site repulsive interaction up to third next nearest neighbors along with the on-site repulsion. The results show that spin-triplet $f$-wave-like pairing can be realized in this system, dominating over singlet d-wave-like pairing, if $2k_F$ spin and $2k_F$ charge fluctuations coexist.
Categories: cond-mat.str-el cond-mat.supr-con