Recent Developments in Organic Superconductors

Abstract

Superconductivity of radical ion salts is now well established in two families of organic conductors: the quasi-one-dimensional (Q-1-D) family, to which the prototype material (TMTSF)₂PF₆ belongs, with T_c in the one Kelvin range, and the two-dimensional series with T_c up to 10 K, which is illustrated by salts such as (BEDT-TTF)₂X i.e. (ET)₂X with X = I₃, Aul₂, Cu(NCS)₂, etc... We first recall the instabilities which are inherent to the (TMTTF-TMTSF)₂X series, giving, as examples, the behaviour, under pressure, of the newly synthesized mixed sulfur-selenium compound (TMDTDSF)₂PF₆, and the discovery of a hidden spin density wave (SDW) phase in (TMTSF)₂ReO₄. Secondly, we present recent experimental results about the quantization of the Hall constant in the field-induced semimetallic states of (TMTSF)₂PF₆ under pressure, and the observation of giant magnetoresistance oscillations in the high-T_c phase of β-(BEDT-TTF)₂I₃, illustrating the two-dimensional character of the latter superconductor.