Superlattice Induced by Charge Order in the Organic Spin Chain (TMTTF)$_2X$ ($X=$ SbF$_6$, AsF$_6$ and PF$_6$) Revealed by High Field EPR

TL;DR

This study uses high-field EPR to reveal a superlattice caused by charge order in quasi-one-dimensional TMTTF salts, showing magnetic decoupling of spin chains and providing insights into interchain interactions.

Contribution

It uncovers a superlattice structure induced by charge order and quantifies interchain interactions using high-field EPR in TMTTF salts.

Findings

Superlattice caused by charge order was observed.

Interchain magnetic interaction is less than 1 mK.

High-field EPR effectively probes charge and spin structures.

Abstract

We have investigated the charge ordering phase of the quasi one dimensional quantum antiferromagnet (TMTTF)$_2X$ ($X=$ SbF$_6$, AsF$_6$ and PF$_6$) using high fields/frequencies electron paramagnetic resonance. In addition to the uniform displacement of the counter anions 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.