GENERIC PHASE-DIAGRAM FOR VORTEX MATTER VIA A STUDY OF PEAK EFFECT PHENOMENON IN CRYSTALS OF 2H-NBSE2

The disordering of a flux line lattice (FLL) is studied in weak pinnin g single crystal samples of the layered low-T-c superconductor NbSe2 c ontaining varying amounts of quenched disorder. The phenomenon of the peak effect, i.e., an anomalous peak in the critical current, attribut ed to a collapse of the correlated Volume of the pinned FLL, shows a r ich evolution as the quenched disorder is varied. The experimental res ults demonstrate (i) the effect of disorder on the peak effect boundar y in the (H, T) space, (ii) the appearance of a new disorder induced t ransformation at the onset of the peak effect that is attributed to a transformation of a topologically ordered FLL to a plastically deforme d one, (iii) a two-step process that leads to the amorphization of the FLL, and (iv) the appearance of strong metastability and history depe ndence of the magnetic response of the system. These results elucidate the combined effects of quenched disorder and thermal fluctuations on the stability of the ordered lattice and on the transformation proces s into glassy disordered phases. The experimentally constructed 'gener ic phase diagram' is compared with theoretically expected behavior of vortex matter with quenched disorder. (C) 1998 Published by Elsevier S cience B.V. All rights reserved.