Abstract
The study of the anion ordered (TMTSF)2ClO4(1 − x)ReO4x solid solution in the limit of a low ReO4− substitution level (0 ⩽ x ⩽ 17%) has revealed a new and interesting phase diagram. Superconductivity is drastically suppressed as the effect of ReO4− non-magnetic point defects increases following the digamma behaviour for usual superconductors in the presence of paramagnetic impurities. Then, no long-range order can be stabilized above 0.1 K in a narrow window of substitution. Finally, an insulating SDW ground state in ReO4−-rich samples is rapidly stabilized with the decrease of the potential strength leading to the doubling of the transverse periodicity. This extensive study has shown that the superconducting order parameter must change its sign over the Fermi surface.