Commensurability of the Spin-Density-Wave State of(TMTSF)PF62Observed byC13-NMR

A spin-density-wave (SDW) for $(\mathrm{TMTSF})_{2}\mathrm{PF}_{6}$ has been reported to appear below ${T}_{\mathrm{SDW}}$ ($\ensuremath{\simeq}12\text{ }\text{ }\mathrm{K}$), with a subphase transition at ${T}^{*}$ ($\ensuremath{\simeq}4\text{ }\text{ }\mathrm{K}$). To determine the structure of the subphase, we synthesized $(\mathrm{TMTSF})_{2}\mathrm{PF}_{6}$, in which one side of the central carbon bond in each TMTSF molecule was replaced by $^{13}\mathrm{C}$, and utilized this compound in $^{13}\mathrm{C}$ nuclear magnetic resonance measurements. Below ${T}_{\mathrm{SDW}}$, the spectrum became broad and ${T}_{1}^{\ensuremath{-}1}$ decreased, in agreement with previous results. Below ${T}^{*}$, fine structures emerged in the center of the spectrum and ${T}_{1}^{\ensuremath{-}1}$ decreased exponentially. These phenomena were attributed to the emergence of commensurability at ${T}^{*}$.