The search for new superconductors at argonne national laboratory

Abstract

The organic superconductors program at Argonne National Laboratory was started by Jack M. Williams in 1981. Initial studies centered around structural effects in the TMTSF salts. Since 1984, the major emphasis has been on salts of the electron donor bis(ethylenedithio)tetrathiafulvalene (ET). Important milestones include the discovery of a number of new superconductors, among them: β-(ET) 2 IBr 2 (T c =2.8 K) and β-(ET) 2 AuI 2 (T c =4−5 K). These salts led to the first structure-properties relationship in ET salts. κ-(ET) 2 Cu[N(CN) 2 ]Br (T c =11.8 K, ambient pressure) and κ-(ET) 2 Cu[N(CN) 2 ]Cl (T c =12.5 K at 0.3 kbar pressure) are still the cation radical superconductors with the highest known transition temperatures. The families of κ L - and κ H -(ET) 2 [M(CF 3 ) 4 ](solvent) salts (T c =2−11 K) yielded at least 25 new closely related organic superconductors with M=Cu, Ag, Au, and solvent=1,1,2-trihaloethane. β″-(ET) 2 SF 5 CH 2 CF 2 SO 3 (T c =5 K) was the first superconductor where both the radical cation and the charge balancing anion were organic. Recent results in the synthesis and characterization of ET salts with anions similar to SF 5 CH 2 CF 2 SO 3 − are presented.