期刊
JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN
卷 69, 期 3, 页码 805-820出版社
PHYSICAL SOC JAPAN
DOI: 10.1143/JPSJ.69.805
关键词
charge ordering; organic conductors; BEDT-TTF; extended Hubbard model; Hartree approximation
The charge ordering phenomena in quasi two-dimensional 1/4-filled organic compounds (ET)(2)X (ET=BEDT-TTF) are investigated theoretically for the theta and alpha-type structures, based on the Hartree approximation for the extended Hubbard models with both on-site and intersite Coulomb interactions. It is found that charge ordered states of stripe-type are stabilized for the relevant values of Coulomb energies, while the spatial pattern of the stripes sensitively depends on the anisotropy of the models. By comparing the results of calculations with the experimental facts, where the effects of quantum fluctuation is incorporated by mapping the stripe-type charge ordered states to the S = 1/2 Heisenberg Hamiltonians, the actual charge patterns in the insulating phases of theta-(ET)(2)MM'(SCN)(4) and alpha-(ET)(2)I-3 are deduced. Furthermore, to obtain a unified view among the theta, alpha and kappa-(ET)(2)X families, the stability of the charge ordered state in competition with the dimeric antiferromagnetic state viewed as the Mott insulating state, which is typically realized in kappa-type compounds, and with the paramagnetic metallic state, is also pursued by extracting essential parameters.
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