Novel superconducting phenomena in quasi-one-dimensional Bechgaard salts

It is the saturation of the transition temperature T c in the range of 24 K for known materials in the late sixties that triggered the search for additional materials offering new coupling mechanisms leading in turn to higher T c 's. As a result of this stimulation, superconductivity in organic matter was discovered in tetramethyl-tetraselenafulvalene-hexafluorophosphate, ( TMTSF ) 2 PF 6 , in 1979, in the laboratory founded at Orsay by Professor Friedel and his colleagues in 1962. Although this conductor is a prototype example for low-dimensional physics, we mostly focus in this article on the superconducting phase of the ambient-pressure superconductor ( TMTSF ) 2 ClO 4 , which has been studied most intensively among the TMTSF salts. We shall present a series of experimental results supporting nodal d -wave symmetry for the superconducting gap in these prototypical quasi-one-dimensional conductors.