Transfer Integrals and the Spatial Pattern of Charge Ordering in θ-(BEDT-TTF)_2RbZn(SCN)_4 at 90 K(Condensed Matter : Structure, Mechanical and Thermal Properties)

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θ-(BEDT-TTF)_2RbZn(SCN)_4 is a two-dimensional organic conductor exhibiting a metal-insulator transition at T_<MI> = 200K. This insulating charge ordered state below Tm was investigated by a single crystal structural analysis taking account of the superlattice formation below T_<MI>. A large displacement (about 0.2Å) of BEDT-TTF molecules associated with the transition was found. Transfer integrals between BEDT-TTF molecules were also calculated from the structural data. The two-dimensional net of transfer integrals above T_<MI> was modulated into the quasi one-dimensional transfer integral chain by the superlattice formation below T_<MI>. The ionicities of BEDT-TTF molecules are estimated from the intramolecular bond length distribution. As a result, charge disproportionation between BEDT-TTF molecules was found, and the ionicity was 0 to +0.2 and +0.8 to +1.0 respectively. The hole-rich sites are laid on the quasi one-dimensional transfer integral chain. We conclude that the spatial pattern of charge ordering is a stripe alternating along the c-axis.
社団法人日本物理学会の論文
2004-01-15