Effects of Randomness on Critical Temperature of Organic Superconductors

The strong reduction of the critical temperature, T c , of organic superconductors (TMTSF) 2 PF 6 , irradiated by X-ray is shown to be understood within the framework of dirty singlet superconductors in the weakly localized regime; i.e. the enhancement of the Coulomb repulsion due to randomness. In the case of the proton-irradiation the reduction of T c experimentally observed is larger and may be ascribed to magnetic defects as suggested before. In the system with two superconducting states such as (BEDT-TTF) 2 I 3 , relative reduction of T c should depend on whether it is caused by the localization effect or by the pair breaking with magnetic defects, and then the origin of the reduction will be identified.