Structural studies of the CDW interaction with defects

We present new X-ray diffuse scattering effects due to pinning of the phase of charge density waves (CDW's) on defects. The coherence between the position of a defect and the phase of a 2k F periodic lattice distortion gives rise to an asymmetry of the +2k F /-2k F diffuse intensity with respect to the layers of main Bragg reflections. This effect, negligible in the weak pining limit, becomes dominant for strong pinning. In addition, CDW phase distortions around defects produce an asymmetry of each individual 2k F diffuse lines. We first calculate the scattered intensity in these different cases that we illustrate by experimental results taken from charge transfer organic salts of the TTF-TCNQ family