VORTEX LATTICE MELTING IN MULTILAYERS WITH VARIABLE ANISOTROPIES

Vortex lattice melting is investigated by transport measurements on Nb Ge/Ge multilayers as a function of Ge thickness, which controls the an isotropy of the system. Considerable changes are found between Ge thic knesses of 2 and 4 nm. For low anisotropies the melting line for the m ultilayers is indistinguishable from that for a single film with the s ame total thickness. Increasing the anisotropy, a crossover is observe d from 2D melting in the full sample at low fields to 2D melting in si ngle layers at high fields, with melting of 3D nature in the intermedi ate field range. Multilayers with high anisotropy only show the second crossover.