Competition and coexistence of bond and charge orders in (TMTTF)2AsF6

(TMTTF) 2 AsF 6 undergoes two phase transitions upon cooling from 300 K. At T C O = 103 K a charge ordering (CO) occurs, and at T S P (B = 9 T) = 11 K the material undergoes a spin-Peierls transition. Within the intermediate, CO phase, the charge disproportionation ratio is found to be at least 3:1 from 1 3 C NMR T - 1 1 measurements on spin-labeled samples. Above T S P up to about 3T S P T - 1 1 is independent of temperature, indicative of low-dimensional magnetic correlations. With the application of about 0.15 GPa pressure, T S P increases substantially, while T C O is rapidly suppressed, demonstrating that the two orders are competing. The experiments are compared to results obtained from calculations on the one-dimensional extended Peierls-Hubbard model.