Symmetry of the superconducting order parameter in Bechgaard salts

Two decades after the discovery of superconductivity in a Bechgaard salt, the pairing mechanism is not yet identified. The first step towards such an identification is to determine the symmetry of the superconducting order parameter. Results on heat transport in the superconducting state of (TMTSF)2ClO4 indicate a finite gap all over the Fermi surface. The magnitude of this gap is confirmed by the first experiments done on break junctions. A nodeless gap imposes a number of constraints on the symmetry of the order parameter,