D-Wave-like nodal superconductivity in the organic conductor (TMTSF) ₂ClO ₄

We suggest theoretical explanation of the high upper critical magnetic field, perpendicular to conducting chains, Hc2 ^b′, experimentally observed in the superconductor (TMTSF) ₂ClO ₄, in terms of singlet superconducting pairing. In particular, we compare the results of d-wave-like nodal, d-wave-like node-less, and s-wave scenarios of superconductivity. We show that, in d-wave-like nodal scenario, superconductivity can naturally exceed both the orbital upper critical magnetic field and Clogston-Shandrasekhar paramagnetic limit as well as reach experimental value, Hc2 ^b′≃6T, in contrast to d-wave-like node-less and s-wave scenarios. In our opinion, the obtained results are strongly in favor of d-wave-like nodal superconductivity in (TMTSF) ₂ClO ₄, whereas, in a sister compound, (TMTSF) ₂PF ₆, we expect either the existence of triplet order parameter or the coexistence of triplet and singlet order parameters.