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

In the organic one-dimensional conductor TMTTF-TCNQ, the 2 k F and the 4 k F CDW were found by the diffuse X-ray photographic method. The 2 k 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 4 k 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 2 k F CDW grows on both TCNQ and TMTTF stacks. However the 4 k F CDW is expected to be present mostly on the TMTTF stack.