Upper critical field Hc2 in Bechgaard salts (TMTSF)2PF6

The symmetry of the superconductivity in Bechgaard salts is still unknown, though the triplet pairing has been established by Hc2 and NMR for (TMTSF)2PF6. The large upper critical field at T = 0K (Hc2 ~ 5 Tesla) both for H || a and H || b also indicates strongly the triplet pairing. Here we start with a low energy effective Hamiltonian and study the temperature dependence of the corresponding Hc2(T)'s. The present analysis suggests that one chiral f-wave superconductor should be the most likely candidate near the upper critical field.