AC response of 2H–NbSe2 single crystals with electron-irradiation-induced defects

Abstract

The generation of defects in NbSe2 single crystals by electron irradiation has been investigated by a combination of acsusceptibility and structural measurements. Remarkably, thanks to the layered structure ofNbSe2, we show that electronic irradiation cannot only create point defects butalso in-plane extended defects, which modify anisotropically the ac response.Indeed, the analysis of the onset of the nonlinear susceptibility response,Hacl(T), as a function of irradiation dose and field orientation shows a correlatedincrease in the density of anisotropic defects induced by electron irradiation.Also, we measured a decrease in the strength of the pinning (Labusch) constantαL accounting for elastic vortex oscillations within the linear Campbell regime forhigh-dose-irradiated samples in a transverse field, again compatible with the presenceof planar defects hindering vortex pinning. X-ray powder diffraction and TEMelectron diffraction measurements suggest these in-plane defects may result fromthe rupture of Se–Se bonds and the formation of nanorods and nanowires byNbSe2 sheet rolling.