A phenomenological model of the superconducting state of the Bechgaard salts

We present a group theoretical analysis of the superconducting state of the Bechgaard salts, e. g., (TMTSF)(2)PF6 and (TMTSF)(2)ClO4 (TMTSF: tetramethyltetraselenafulvalene). We show that there are eight symmetry distinct superconducting states. Of these, only the ( fully gapped, even frequency, odd parity, triplet) 'polar state' is consistent with the full range of the experiments on the Bechgaard salts. The gap function of the polar state is d(k) proportional to (psi(uk), 0, 0), where psi(uk) may be any odd parity function that is translationally invariant. This analysis also predicts that a phase transition, between two superconducting phases, occurs in weak magnetic fields.