Spiral Charge Frustration in the Molecular Conductor (DI-DCNQI)₂Ag

We theoretically study the effect of spiral-type charge frustration in a quasi-one-dimensional molecular conductor (DI-DCNQI)₂Ag. We clarify how the spiral frustration in the interchain Coulomb repulsion is relieved and leads to a self-organization of complex charge-lattice ordered chains, in agreement with the recent synchrotron x-ray study [ T. Kakiuchi et al. Phys. Rev. Lett. 98 066402 (2007)]. In addition, we find that a keen competition between charge and lattice degrees of freedom under the frustration gives rise to a characteristic temperature within the ordered phase, below which a drastic growth of molecular displacements occurs. Our results enlighten the relevance of the spiral frustration and provide a possible reconciliation among puzzling experimental data.