Evidence for superconductivity in ${\mathrm{}(\mathrm{B}\mathrm{E}\mathrm{D}\mathrm{T}-\mathrm{T}\mathrm{T}\mathrm{E})\mathrm{}}_4$${\left(\mathrm{R}\mathrm{e}{\mathrm{O}}_4\right)}_2$ [where BEDT-TTF is bis (ethylenedithiolo)tetrathiafulvalene] near 2 K for pressures above 4 kbar is reported. This is the first unambiguous observation of superconductivity in a sulfur-donor organic system. At higher pressures the transition temperature decreases rapidly, $\frac{d{T}_c}{\mathrm{dP}}\sim -0.3\mathrm{}$ K/kbar. At low pressures this material exhibits a first-order metal-insulator transition, postulated to result from a change in the arrangement of the anions which are ordered at room temperature.

• Received 8 November 1982

DOI:https://doi.org/10.1103/PhysRevLett.50.270