Charge frustration and novel electron-lattice phase transition in molecular conductor DCNQIAg

Seo, Hitoshi

We have theoretically investigated the phase transition accompanying charge ordering in 1/4-filled quasi-one-dimensional organic conductor DI-DCNQIAg. The nature of this phase transition at 220 K has been under debate since the first direct observation of charge ordering among organic conductors by Hiraki and Kanoda. In this study, motivated by a recent synchrotron radiation X-ray study by Kakiuchi et al., we investigate a three-dimensional interacting spinless fermion model coupled to the lattice degree of freedom. We have found that the peculiar "spiral frustration" existing in the interchain Coulomb interaction destabilizes simple Wigner crystal-type charge order and gives rise to a novel state where different chains show different orders and align periodically: charge order, lattice dimerization, and a co-existence of them.