Dynamic properties of commensurate and incommensurate spin density waves as probed by 13C NMR

Abstract We have measured 13 C NMR lineshape and nuclear spin lattice relaxation in the spin-density-wave (SDW) state of (TMTTF) 2 Br and (TMTSF) 2 PF 6 . The incommensurability of the SDW in (TMTSF) 2 PF 6 is confirmed, and we show that the phason mode is dominant in the relaxation. However, we found that (TMTTF) 2 Br is commensurate and estimated that the SDW amplitude is small. No phason contribution to the relaxation is observed in this compound. We discuss some implications for theory.