ELECTRONIC-STATE OF KAPPA-(BMDT-TTF)(2)AU(CN)2 STUDIED BY NMR AND THERMOELECTRIC MEASUREMENTS

The electronic state of kappa-(BMDT-TTF)(2)Au(CN)(2) was investigated by measurements of H-1-NMR and thermoelectric power. In H-1-NMR, the p rofile of the nuclear relaxation curve changed drastically at 75 K fro m exponential time-dependence to non-single exponential one reflecting inhomogeneous relaxation. This change evidences a transition in the e lectronic state at this temperature. However, the longest T-1 below th e transition temperature behaves like a Korringa law, suggesting that the low-temperature state is another metallic state. The thermoelectri c power shows a strong anomaly around 75 K,being consistent with the N MR results. Above that, the temperature dependence is similar to that found in the K phase of BEDT-TTF compounds, suggesting a similar Fermi -surface topology. These results suggest that the transition at 75 K i s not a conventional metal-to-insulator transition but a metal-to-meta l transition.