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

The generation of defects in NbSe(2) single crystals by electron irradiation has been investigated by a combination of ac susceptibility and structural measurements. Remarkably, thanks to the layered structure of NbSe(2), we show that electronic irradiation cannot only create point defects but also in-plane extended defects, which modify anisotropically the ac response. Indeed, the analysis of the onset of the nonlinear susceptibility response, H(ac)(l)(T), as a function of irradiation dose and field orientation shows a correlated increase in the density of anisotropic defects induced by electron irradiation. Also, we measured a decrease in the strength of the pinning (Labusch) constant α(L) accounting for elastic vortex oscillations within the linear Campbell regime for high-dose-irradiated samples in a transverse field, again compatible with the presence of planar defects hindering vortex pinning. X-ray powder diffraction and TEM electron diffraction measurements suggest these in-plane defects may result from the rupture of Se-Se bonds and the formation of nanorods and nanowires by NbSe(2) sheet rolling.