Anion Ordering and Optical Properties of the Quasi-One-Dimensional Organic Conductor (ChTM-TTP)_2GaCl_4(Condensed Matter : Electronic Structure, Electrical, Magnetic and Optical Properties)

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Low-temperature crystal structure and optical properties of the quasi-one-dimensional organic conductor (ChTM-TTP)_2GaCl_4 (ChTM-TTP : 2-[4,5-(1,2-cyclohexylenedithio)-1,3 -dithiol-2-ylidene]-5-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene) have been investigated. As the temperature lowers,the disordered anion transforms to an ordered state with a superstructure wave vector of q = (2/1, 0, 2/1). The peak intensities of the superlattice gradually increase in the metallic region,and are saturated below 150 K; this indicates that the charge localization below 150 K is independent of the evolution of the superlattice. The reflectance spectra of (ChTM-TTP)_2X suggest the existence of moderate interchain interactions. The transverse interactions are more pronounced in the GaCl_4 salt(t⊥/t_‖≈1/7) than the AuBr_2 and Au(CN)_2 salts. The low-temperature optical reflectance of the GaCl_4 salt shows no significant change, indicating that (ChTM-TTP)_2GaCl_4 goes to an insulating state with a small charge gap, which is consistent with the transport property. The low-frequency peak in the chainaxis optical conductivity is attributed to a correlation gap, though the expected on-site Coulomb repulsion U is relatively small.
社団法人日本物理学会の論文
2002-12-15