Vortex lattice melting in multilayers with variable anisotropies

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Abstract
Vortex lattice melting is investigated by transport measurements on NbGe/Ge multilayers as a function of Ge thickness, which controls the anisotropy of the system. Considerable changes are found between Ge thicknesses of 2 and 4 nm. For low anisotropies the melting line for the multilayers is indistinguishable from that for a single film with the same total thickness. Increasing the anisotropy, a crossover is observed from 2D melting in the full sample at low fields to 2D melting in single layers at high fields, with melting of 3D nature in the intermediate field range. Multilayers with high anisotropy only show the second crossover.