Influence of charge order on the ground state of TMTTF conductors

Properties of the charge-ordered (CO) phase for the representative salt (TMTTF)(2)AsF6 are determined using C-13 and As-75 nuclei as probes. The charge disproportionation ratio is found to be at least 3:1 at temperatures below the transition temperature T-CO. At lower temperatures, the material undergoes a second transition to a singlet ground state. Investigations of the relative stability of the two orders under applied pressure reveal that the two orders compete. The phase diagram consists of a region of coexistence and a tetracritical point.