Effect of Diorder on the Peak Effect and Structure of Flux Line Lattice in 2H-NbSe2

The effect of disorder on flux line lattice (FLL) melting is studied via the Peak Effect phenomenon. On the upper branch of the Peak Effect curve, where this effect is more robust, we observe a stepwise disordering of the FLL, suggesting two first order transition spanning the Peak Effect region. The lower part of the curve is found to be strongly affected by disorder. Both the branch and the "nose", i.e., the turnaround of the curve, dissapear in systems with stronger disorder and the observed results are consitent with the line seperating a disentangled liquid or a glass from an entangled flux liquid.