X-ray scattering evidence for macroscopic strong pinning centers in the sliding CDW state of NbSe3

Using high-resolution X-ray scattering techniques, we have measured the wave vector of the sliding charge density wave as a function of beam position, along the length of NbSe₃ whiskers. We show that structural imperfections and radiation-induced defects increase locally the CDW pinning force, and give rise to CDW phase distortions. Using the semi-microscopic model of Brazovskii et al. (Phys. Rev. B, 61 (2000) 10640) describing the normal leftrightarrow condensed carrier conversion, with spatially varying parameters, we account for the experimental spatial dependence of the CDW phase gradient near both types of defects.