Structural studies of the CDW interaction with defects

Abstract
We present new X-ray diffise 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 2 k p~eri odic lattice distortion gives rise to an asymmetry of the +2k~/-2kd iffise intensity with respect to the layers of main Bragg reflections. This effect, negligible in the weak pinning limit, becomes dominant for strong pinning. In addition, CDW phase distortions around defects produce an asyrnmetry of each individual 2+ 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.