FLUX DROPLET FORMATION IN NBSE2 SINGLE-CRYSTALS OBSERVED BY DECORATION

A potential barrier of geometrical origin, characterized by a barrier field H-p, governs vortex penetration in thin superconducting samples. We observed this effect by the decoration of crystals of NbSe2. Upon zero field cooling and applying a field H-a < H-p approximate to 5 mT, vortices form a belt at the sample edges. At H-a approximate to H-p f lux begins to penetrate in the form of dropletlike intrusions. The ori entational correlation length for the vortex pattern inside the ''drop lets'' is much larger than for the field-cooled patterns. This we inte rpret as recrystallization of the moving flux line lattice.