DIMENSIONAL CROSSOVER IN FRACTAL MULTILAYERED SUPERCONDUCTORS

Superconducting properties of multilayers consisting of alternating Nb and Cu layers with a fractal stacking sequence have been investigated . Dimensional crossover is observed in the temperature dependence of t he parallel critical magnetic field B-c2// from ''fractal behaviour'' near T-c where B-c2// similar to (1-T/T-c)(f) with 0.5 < f < 1 to two dimensional behaviour B-c2// similar to (1-T/T-c)(1/2) below a crossov er temperature T-cr T-cr strongly depends on the fractal dimension Dfo f the multilayered superconductor.