Symmetries of the quasi-1D Bechgaard salts superconducting state in an applied magnetic field

We investigate the possible superconducting pairing symmetries which would account for the latest experimental results on the Bechgaard salts. Using a renormalization group (RG) technique we calculate the couplings of the singlet and triplet interactions in the quasi-1D Hamiltonian. In the presence of interchain interactions, the singlet and triplet couplings are of the same order of magnitude. The renormalized couplings are then used in an RPA calculation to evaluate the critical fields of superconductivity for the two dominant order parameter symmetries in the RG flow, i.e., the d$_{x^{2}-y^{2}}$ and fy symmetries. It is shown that, for the standard values of the anisotropy ratio of the Fermi surface, the critical fields of the singlet symmetry are strongly reduced. A re-entrant superconductivity is however still present for the triplet state.