Determination of Charge Ordered Structure in (DI-DCNQI)2Ag using Synchrotron Radiation X-ray Diffraction

Department of Materials Structure Science, The Graduate University for Advanced Studies* Institute of Materials Structure Science, High Energy Accelerator Research Organization, Japan** Department of Applied Physics, University of Tokyo, Japan***
â—‹Toru Kakiuchi* Yusuke Wakabayashi** Hiroshi Sawa** Tetsuaki Itou*** Kazushi Kanoda***

Recently, charge ordering (CO) phenomena are attracting considerable attention. Many investigations about CO materials have been performed in order to make clear how the electronic correlation stabilizes CO state.
Organic salt (DI-DCNQI)2Ag, a typical pseudo one-dimensional electronic structure material, is one of such CO materials.[1] Although Hiraki et al. proposed Wigner crystal type of CO as the ground state based on their NMR measurement,[2] the CO structure is still unsolved because the real crystal has complicated three-dimensional interaction.
We have conducted a full-structure analysis in order to clarify the CO structure in this compound. The measurement was made at BL1A at the Photon Factory, KEK, Japan with using imaging plate Weissenberg camera attached with displex. Obtained low-temperature structure shows that the CO coexists with bond order wave (BOW) accompanied with dimerization. This is due to frustration among the DCNQI column. In spite of the peculiar structure, charge distribution (black clouds in the figure show charge rich area schematically) was concluded as a simple body centered Wigner crystal.
[1] H. Seo and H. Fukuyama, J. Phys. Soc. Jpn. 66 1249(1997)
[2] K. Hiraki and K. Kanoda, Phys. Rev. Lett. 80 4737(1998)