Superlattice Induced by Charge Order in the Organic Spin Chain (TMTTF)2X (X = SbF6, AsF6, and PF6) Revealed by High-Field Electron Paramagnetic Resonance.

We have investigated the charge ordering phase of the quasi-one-dimensional quantum antiferromagnet (TMTTF)2X (X = SbF6, AsF6, and PF6) using high-fields/frequency electron paramagnetic resonance. In addition to the uniform displacement of the counteranions involved in the charge-order phase, we report the existence of a superlattice between the spin chains in the direction c, caused by the space modulation of the charge order. When the field is high enough, the magnetic decoupling of the spin chains allows us to estimate the interaction between the chains, J c < 1 mK, three orders of magnitude lower than expected from the mean field theory.