Re-entrant peak effect in an anisotropic superconductor 2H − NbSe₂: role of disorder

The influence of disorder (induced by pinning centres) on the peak effect (PE) phenomenon, namely, an anomalous increase in J_c vs. H (or T), has been studied in the anisotropic superconductor 2H-NbSe₂. Results from new electrical transport as well as dc and ac magnetic response studies are presented to demonstrate that increasing disorder shrinks the (H, T) parameter space over which the vortex lattice retains spatial order. We find that the re-entrant nature of PE is clearly manifested only in crystals which have moderate amount of disorder. We also find that the upper branch of the PE curve is fairly robust, whereas the lower re-entrant branch is strongly affected by disorder