Organic superconductors: The Bechgaard salts and relatives

Abstract

Organic conductors were originally considered a route to achieving high temperature superconductivity. While that goal could not be met, what came to be was a class of materials in which the interplay between correlations and dimensionality, and sometimes geometric frustration, lead to a spectacular diversity of phases and phenomena that are tuned by magnetic field, pressure, and temperature. Highlighted here are the physical properties of the superconducting and normal states of the first family of organic superconductors, the quasi-one dimensional Bechgaard salts (TMTSF)2X, as well as the quasi-two dimensional compounds κ-(BEDT-TTF)2X. In both cases, the preponderance of experiments indicate that the superconductivity is nodal. As well, the importance of correlations is evident in the temperature/pressure phase diagrams, and the influence of low-energy magnetic fluctuations over the normal state properties above the superconducting transition temperature is substantial.