title: Organic metal (EDO-TTF)2PF6with multi-instability.
abstract: The multi-instability of the electronic structure of (EDO-TTF)2PF6, where EDO-TTF means ethylene-dioxytetrathiafulvalene, is reviewed. This complex showed the metal-insulator transition at 280 K associated with distinct molecular deformations. The mechanism is interpreted as the cooperation of Peierls transition, charge ordering, and the order-disorder transition of the countercomponent. The charge ordering pattern in the low-temperature phase is of the novel [0, 0, 1, 1] type. The sensitivity of the electronic state to external perturbations is demonstrated applying not only static but also instantaneous stimuli. In the latter case, the photo-induced phase transition is ultrafast and highly efficient. One photon causes the transition of several hundreds of donor molecules in the low-temperature phase to relax into a highly conducting metastable state within about 1.5 ps. In the early stage of the transient state, the charge ordering of the [1, 0, 1, 0] type occurs. As for the chemical modifications of this material, the partial deuteration of this complex increases the metal-insulator transition temperature. The introduction of a methyl group greatly modulates the electronic structure of the complex, i.e. (methyl-EDO-TTF)2X (X=BF4, ClO4) shows a two-dimensional electronic structure. The working hypotheses for developing the systems with multi-instability are described.
authors.affiliation: Research Center for Low Temperature and Materials Sciences, Kyoto University, Sakyo-ku, Kyoto 606-8501, Japan; Nonequilibrium Dynamics Project, ERATO/JST, Tsukuba, Ibaraki 305-0801, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Yamochi
authors.affiliation: Nonequilibrium Dynamics Project, ERATO/JST, Tsukuba, Ibaraki 305-0801, Japan; Department of Materials Science, Tokyo Institute of Technology, Meguro-ku, Tokyo 152-8551, Japan.
authors.forename: Shin-Ya
authors.initials: SY
authors.lastname: Koshihara
keywords: charge ordering; molecular conductor; molecular deformation; multi-instability; photo-induced phase transition