Redistribution of electronic charges in spin-Peierls state in (TMTTF)2AsF6 observed by 13C NMR

We report ^{13}C NMR spectra and nuclear spin lattice relaxation rate 1/T_1 for a quasi-one-dimensional quarter-filled organic material (TMTTF)_{2}AsF_{6}, which undergoes charge ordering (T_{CO} = 102 K) and spin-Peierls phase transitions (T_{SP} = 14 K). The ratio of two 1/T_1 for the charge accepting and donating TMTTF sites which grows from T_{CO} finally saturates in approaching T_{SP}, indicating one spin correlation function even in the charge ordered state. Below T_{SP}, however, the doubly split NMR lines from inequivalently charged molecules merge into one line, originated from the variation in charge densities. This shows that a rearrangement of the charge configuration occurs at T_{SP}.

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