A new 9 K superconducting organic salt composed of the bis (ethylenedithio) tetrathiafulvalene (ET) electron-donor molecule and the tetrakis (trifluoromethyl) cuprate (III) anion, [Cu(CF 3) 4] -

Abstract

We report the discovery of a second, higher- T c superconducting organic charge-transfer salt derived from the electron-donor molecule BEDT-TTF (or ET), the novel organometallic anion [Cu(CF 3) 4] −, and the neutral solvent molecule 1, 1, 2-trichloroethane (TCE). We have very recently reported that this charge-transfer system yields a new superconducting ϰ phase salt, ϰ L- (ET) 2Cu(CF 3) 4·TCE, with inductive onset T crmc =4.0 K at ambient pressure. This ϰ phase salt (ϰ denotes a particular packing arrangement of the ET organic donor molecules) is electrocrystallized in the habit of hexagonal plates. Crystals possessing a needle-like habit electrocrystallize simultaneously with these plates, and we find these needles to be a distinctly different superconducting phase with diamagnetic onset T c=9.2±0.1 K at ambient pressure. On the basis of our experiments, we denote this new superconducting phase as ϰ H −( ET) 2 Cu( CF 3) 4·( TCE) x , X<1.