Transverse correlations and plasticity in the CDW conductor NbSe₃ studied by X-ray microbeam diffraction

Abstract
In whisker-like samples of the quasi-1D conductor NbSe₃, the presence of longitudinal steps causes shearing of the CDW, and leads to a loss of transverse correlations. We use a microdiffraction setup with a spatial resolution of 300 nm and an angular sensitivity of 5 mdeg to image the resulting CDW contrast between thick and thin portions of the sample. Microdiffraction in the b* - c* plane shows that depinning on the thick, weakly pinned side is accompanied by the loss of diffraction intensity, demonstrating a loss of correlations in qualitative agreement with previous X-ray diffraction topography measurements¹, but with an order-of-magnitude improvement in spatial resolution. Microdiffraction images in the a* - b* plane reveal a sharp increase in the full width at half maximum in an approximately 1 micron thick region near the step edge and a rotation of the CDW wavevector that varies with applied field. We use the extremal value of the CDW wavevector rotation to estimate the shear modulus of this electronic crystal.