Redistribution of electronic charges in the spin-Peierls state in (TMTTF)$_2$AsF$_6$ observed by $^{13}$C NMR

We report he results of $^{13}$C NMR for a quasi-one-dimensional quarter-filled organic material (TMTTF)$_{2}$AsF$_{6}$, which undergoes charge ordering ($T_{\textrm{CO}}$ = 102 K) and spin-Peierls phase transitions ($T_{\textrm{SP}}$ = 12 K). The ratio of two $1/T_1$ for the charge accepting and donating sites which grows from $T_\textrm{CO}$ finally saturates in approaching $T_{\textrm{SP}}$, that indicates an opening of single gap for the spin excitation spectra. At $T_{\textrm{SP}}$, however, doubly split NMR lines from inequivalently charged molecules merge originated from the variation in \textit{charge} densities. This shows a rearrangement of the charge configuration in the spin-Peierls state.