Plastic sliding of charge density waves:: X-ray space resolved-studies versus theory of current conversion

We present experimental and theoretical results on the distribution of deformations experienced by a sliding charge density wave (CDW) in connection with the normal =collective current conversion process. High-resolution (30-100 mu m) x-ray measurements of the satellite positional shift q have been performed on NbSe3 whiskers at 90 K. For the first time q has been determined with application of direct, as well as pulsed, currents and in the immediate vicinity of the injection extraction contact. We observe a steep variation of q near the contact that we model in terms of intensive nucleation processes of dislocation loops (DLs) at the host defects. A logarithmic time decay between pulses implies a creep of pinned DLs. A small constant residual gradient in the central part of the sample indicates that the conversion process is incomplete, consistent with a finite DL pinning threshold. On the theory side, general equations are derived to describe inhomogeneous distributions of deformations, electric fields, and currents. Numerical modeling under realistic experimental conditions is combined with model-independent relations. We discuss both similarities and contradictions with earlier studies.