Generic phase diagram for vortex matter via a study of peak effect phenomenon in crystals of 2H-NbSe₂

Abstract

The disordering of a flux line lattice (FLL) is studied in weak pinning single crystal samples of the layered low-T_c superconductor NbSe₂ containing varying amounts of quenched disorder. The phenomenon of the peak effect, i.e., an anomalous peak in the critical current, attributed to a collapse of the correlated volume of the pinned FLL, shows a rich evolution as the quenched disorder is varied. The experimental results demonstrate (i) the effect of disorder on the peak effect boundary in the (H, T) space, (ii) the appearance of a new disorder induced transformation at the onset of the peak effect that is attributed to a transformation of a topologically ordered FLL to a plastically deformed one, (iii) a two-step process that leads to the amorphization of the FLL, and (iv) the appearance of strong metastability and history dependence 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 process into glassy disordered phases. The experimentally constructed 'generic phase diagram' is compared with theoretically expected behavior of vortex matter with quenched disorder.