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 wav e 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 g ive rise to CDW phase distortions. Using the semi-microscopic model of Braz ovskii et al. ( Phys. Rev. B, 61 (2000) 10640) describing the normal conden sed carrier conversion, with spatially varying parameters, we account for t he experimental spatial dependence of the CDW phase gradient near both type s of defects.