X-Ray Scattering Study of 2k_F and 4k_F CDW in TMTTF–TCNQ

Abstract

In the organic one-dimensional conductor TMTTF–TCNQ, the 2k_F and the 4k_F CDW were found by the diffuse X-ray photographic method. The 2k_F CDW condenses at 36 K, at which the metal-insulator transition occurs, and forms three-dimensionally ordered structures indicating the occurence of the Peierls transition. A different and unusual temperature dependence is shown by the 4k_F CDW. The transverse ordering of CDW is easily destroyed by the X-ray irradiation. Observed wave number of the transverse ordering and the strong irradiation effect suggest that the 2k_F CDW grows on both TCNQ and TMTTF stacks. However the 4k_F CDW is expected to be present mostly on the TMTTF stack.