Sulfur-based synthetic metal superconductors

A summary is given of the current status and findings regarding BED-TTF (ET) based synthetic metal superconductors; in particular: β-(ET)2I3 (Tsub(c)=1.4K), β-(ET)2IBr2 (Tsub(c)=2.8K) and β-(ET)2AuI2 (Tsub(c)=5K). The unique crystal packing features of these layer-like systems is described and the role of the linear triatomic halide containing anions is explored. Electronic band structure calculations are in agreement with the 2D nature of the β-(ET)2X structure. These theoretical studies suggest that the superconducting critical temperatures of β-(ET)2X type materials might be increased significantly above presently observed values by the use of different linear anions, or entirely new donor molecule anion combinations. (author)