Ubiquitous Superconductivity Near 4K in Salts of the BEDT-TTF/I System: Is There a Common Source?

Abstract

Abstract An unusually large number of metallic and superconducting phases exist among the organic charge-transfer salts of the BEDT-TTF /I system [BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene]. In addition to the well-known superconducting transitions near 1.4 K and ∼ 8 K in β-(ET)2I3 and β*-(ET)2I3, respectively, superconductivity near 4 K occurs in three other superconducting salts of this system, frequently in other conventionally synthesized salts, and in the products of thermally processed salts and chemically modified syntheses. A critical review of the literature of this system indicates that the source of superconductivity near 4 K in many cases is a β-like phase of (ET)2I3 stoichiometry. It is argued that superconductivity in the γ-(ET)3(I3)2.5 salt (onset Tc ∼ 4 K) has not been persuasively demonstrated and that the source of superconductivity likely is a β-phase component in α-β mixed-phase crystals.