NMR Studies of Exotic Members of Bechgaard Salt with Non- centrosymmetric Anions under Pressure

The electronic properties of (TMTSF) 2FSO 3 have been investigated under pressure of 0.65 GPa by measuring 77Se-NMR lineshape, spin-lattice relaxation rate ( T 1 − 1 ) and spin-spin relaxation rate ( T 1 − 1 ) measurements on a single crystal sample. The NMR signal was found abnormally broadened below 90 K. Below 40 K, a narrow component appears and coexists with the broader one. The temperature dependence of T 1 − 1 suggests that the broader component comes from a metallic phase and the narrow one from an insulating phase. The activation energy determined for the insulating component was found three times lower than the value found at ambient pressure. From the T 1 − 1 measurements, the broadening of the metallic component was confirmed as inhomogeneous. An unusual double peak anomaly of T 1 − 1 suggests the existence of extremely slow fluctuations of the inhomogeneous local fields below 90 K at this pressure.