Tuning Charge Order in (TMTTF)2X by Partial Anion Substitution

In the quasi-one-dimensional (TMTTF)2X compounds with effectively quarter-filled bands, electronic charge order is stabilized from delicate interplay of Coulomb repulsion and bandwidth. The correlation strength commonly tuned by physical pressure or chemical substitution stoichiometric ratios anions cations. Here, we investigate charge-ordered state through partial in (TMTTF)2[AsF6]1−x[SbF6]x x≈0.3, determined intensity infrared vibrations, which sufficient to suppress spin-Peierls state. Our dc transport experiments reveal a transition temperature TCO = 120 K gap ΔCO=430 between values two parent (TMTTF)2AsF6 (TMTTF)2SbF6. Upon plotting parameters for different (TMTTF)2X, find universal relationship ΔCO yielding that energy vanishes temperatures TCO≤60 K. While these quantities indicate macroscopic continuously tuned, our vibrational spectroscopy results probing local disproportionation suggest 2δ modulated on microscopic level.