Charge localization in [(TMTTF)0.5(TMTSF)0.5]2ReO4: a pressure study

A pressure study of the transport properties in the solid solution [(TMTTF)0.5(TMTSF)0.5]2ReO4 with the aim to explore different sources of the charge localization is presented. A pressure independent on-site 4kF potential (besides the bond contribution) weakens in the (0,1/2,1/2) anion ordered phase independent of the long range alternate molecular order. The strength of 4kF site energy is estimated to be 200 K, while it amounts to only 50 K when the molecular order is not present.