Charge Order Breaks Magnetic Symmetry in Molecular Quantum Spin Chains
Figure 6
Crystal structure of , as an example, viewed (a) along the stacking direction , (b) along the -axis and (c) along the direction. The strongest coupling between the octahedral anions and the sulfur atoms is indicated by the red dashed lines I and II which are related by inversion symmetry for . In the charge-ordered state, not only the TMTTF molecules develop a charge disproportionation with alternating charge-rich and charge-poor molecules along the stacks, but also the octahedral anions are slightly distorted. The inversion symmetry is lifted and contact I becomes stronger than II, for instance. Two kinds of domains are formed separated by domain walls preferentially in the or planes. Also shown is the configuration between the TMTTF molecular structure and the principal axes of the g-tensor. Note there exists only one electron per dimer. At elevated temperatures the g-tensor (blue arrows indicate the principal magnetic directions , , and ) is determined by the molecular structure. The -axis of the -tensor is normal to the molecular plane and along the stacking direction, while the -axis points along to the longest molecule extension. For the principal axes of the -tensor rotate around the -axis by an angle in opposite directions, resulting in the brown arrows.
