Competition between triplet, singlet, and FFLO states in organic superconductors (TMTSF)2X under magnetic field

Abstract

We study the competition between triplet f-wave, singlet d-wave, and the FFLO state in a model for (TMTSF)2X using random phase approximation. The result suggests the possibility of singlet →FFLO→triplet transition upon increasing the magnetic field. The singlet →FFLO→triplet transition can appear in a large parameter regime on the space of the magnetic field and the off-site repulsions which induce the coexistence with 2kF charge and 2kF spin fluctuations, although decreasing the off-site repulsions suppresses the spin triplet f-wave pairing. We also show that the triplet component mixing increases in the FFLO state with increasing the magnetic field, and the off-site repulsions increase the mixing rate. The results seem to suggest that the large triplet mixing results in an enhanced tendency toward the FFLO state over the usual pairing state.