Low-temperature metallic state and superconductivity in quasi-one-dimensional organic conductors: pressure and irradiation investigations

The comparison between the disordered metallic state created by irradiation and the metallic regime stabilised by high pressure in TMTSF-DMTCNQ and TMTSF2-PF6 establishes the existence of a contribution from superconducting fluctuations to the conductivity below 50 K. A calculation using Ginzburg-Landau theory is in very good agreement with the experimental temperature dependence of the paraconductivity. It is shown that the metal-insulator transition in TMTSF2-PF6 is shifted by the disorder to a lower temperature. However, the effect is less for the spin-density-wave transition in TMTSF-PF6 than for the charge-density-wave ordering in TMTSF-DMTCNQ. Finally it is shown that the superconductivity transition is strongly depressed by irradiation-induced defects. (author)