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

TL;DR

This paper explores the possible superconducting pairing symmetries in Bechgaard salts under magnetic fields, using renormalization group and RPA methods to analyze critical fields and symmetry competition.

Contribution

It introduces a combined RG and RPA approach to determine the dominant pairing symmetries and their critical fields in quasi-1D superconductors with interchain interactions.

Findings

Singlet and triplet couplings are comparable with interchain interactions.

Critical fields for singlet symmetry are significantly reduced.

Reentrant superconductivity persists for the triplet state.

Abstract

We investigate the possible superconducting pairing symmetries which would account for the latest experimental results on the Bechgaard salts. Using a renormalization group (R.G) 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 R.G flow, i.e, the dx2-y2 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 reentrant superconductivity is however still present for the triplet state.