Charge order in (TMTTF)2PF6 investigated by infrared spectroscopy

We investigated the vibronic modes of the (TMTTF)2PF6 charge transfer salt in the vicinity of the charge-order transition by temperature dependent infrared measurements on single crystals. In the mid-infrared frequency region, we found that the ag(v3) vibronic mode splits for light polarized parallel to the molecular stacks below the charge-order transition which can be directly linked to the charge disproportionation on the (TMTTF)2-dimers. We extracted the temperature dependence the charge disproportionation from a detailed analysis of the resonance frequencies of this mode down to lowest temperatures into the spin-ordered state.