NMR Investigation of Spin Density Wave Critical Fluctuations in (TMTSF)2PF6

We report NMR measurements of the spin density wave (SDW) transition critical fluctuations in (TMTSF)2PF6 at 14.9 MHz and 0.98 GHz. This contribution to 1/T1 is nearly independent of the magnetic field alignment and the frequency on both sides of the transition; above the transition at TN it varies as ¦T − tn¦θ with θ = −0.75 ± 0.08. These observations are consistent with dynamical scaling for the 3D Heisenberg model and show that the correlation time for the critical fluctuations responsible for t1 is less than 2 × 10−10 s for all temperatures studied. Such behavior is very different from that observed in the ordered SDW phase, where the dominant coupling is to SDW phasons whose characteristic times cover a very broad range.