The case for universality of the phase diagram of the Fabre and Bechgaard salts

We report the observation of superconductivity in the spin-Peierls Fabre sa lt (TMTTF)(2)PF6 from pressure dependent electrical transport measurements above a threshold of 4.35 GPa. The data complete the sequence of ground sta tes of this compound in the temperature and pressure plane adducing an empi rical basis to the universal character of the phase diagram of the Fabre sa lts and their selenide analogues, the Bechgaard salts. The structure of the phase diagram at the approach of the crossover between spin-density wave a nd superconducting states is compared with the results of scaling theory of the interplay between both electronic instabilities under pressure. The co mparison supports the view that magnetism and superconductivity in these co mpounds have a common electronic origin.