Molecular motion and high-temperature paramagnetic phase in Kappa - (BEDT-TTF) sub(2) Cu[N(CN) sub(2) Cl

The organic conductor Kappa -(BEDT-TTF) sub(2) Cu[N(CN) sub(2)] Cl has been studied for the examination of the conducting mechanism of the semiconducting behavior at high temperatures by super(13)C-NMR spectroscopy. We found that the temperature dependence of the linewidths and the spin-spin relaxation rate T super(-1) sub(2) showed a peak structure characterized by the hyperfine coupling constant in this region, suggesting a connection between ethylene motion and conducting electrons similar to that observed in Kappa -(BEDT-TTF) sub(2) Cu(NCS) sub(2). Although Kappa -(BEDT-TTF) sub(2) Cu[N(CN) sub(2)] Cl salt was thought to be an insulator at high temperature, our findings suggest that all Kappa -type salts at high temperatures could be in the same phase where the scattering caused by ethylene motion is added to bad metal.