Superconductivity in percolating niobium films

We have studied the superconducting properties of nanostructured niobium films patterned on top of gold. The niobium was patterned using e-beam lithography to obtain structures with a precisely determined percolation parameter p. The samples include both randomly generated patterns and progressions. All samples are superconducting with transition temperatures in the range 3-5K. The measurements of the resistance as a function of magnetic field for samples with different percolation parameters show a magnetic field driven superconductor insulator transition, which also depends on the distance to the critical percolation threshold. We carried out the finite size scaling analysis, obtained the critical exponents and examined the results in the context of the percolation theory and the universal theory of quantum phase transitions.