SPIN-DENSITY-WAVE STATE IN (TMTSF)(2)PF6 - A SE-77 NMR-STUDY AT HIGH MAGNETIC-FIELDS

We present a nuclear magnetic resonance study of the low-temperature s pin-density-wave (SDW) ground state in the quasi-one-dimensional condu ctor (TMTSF)(2)PF6 amethyl-tetraselenafulvalene)hexafluorophosphate]. Using magnetic fields up to 22 T, we have measured the Se-77 spin-latt ice (T-1(-1)) and spin-spin relaxation rates (T-2(-1)) above and below the SDW transition (T(SDW)approximate to 12 K). Between T-SDW and app roximate to 4 K, we observe anomalously fast and Korringa-like T-1(-1) ; below 4 K, T-1(-1) decays rapidly. A reduction in T-2(-1) is also ob served at 4 K, but the absorption linewidth does not change to within experimental error. We attribute this behavior to an incomplete SDW tr ansition at T-SDW, leaving residual carriers at the Fermi level, and a subsequent consummation of the transition at 4 K. Our data below 4 K are consistent with a simple model of the temperature dependence of T- 1(-1) in a fully gapped and low-dimensional conductor.