REENTRANT PEAK EFFECT IN AN ANISOTROPIC SUPERCONDUCTOR 2H-NBSE2 - ROLE OF DISORDER

The influence of disorder (induced by pinning centres) on the peak eff ect (PE) phenomenon, namely, an anomalous increase in J(c) vs. H (or T ), has been studied in the anisotropic superconductor 2H-NbSe2. Result s from new electrical transport as well as de and ac magnetic response studies are presented to demonstrate that increasing disorder shrinks the (H, T) parameter space over which the vortex lattice retains spat ial order. We find that the re-entrant nature of PE is clearly manifes ted only in crystals which have moderate amount of disorder. We also f ind that the upper branch of the PE curve is fairly robust, whereas th e lower re-entrant branch is strongly affected by disorder.