Critical currents and pinning forces in the PB - GE system

We have studied critical current densities Jc, pinning force densities P and resistivities ρ in co-evaporated Pb-Ge mixtures in the range Vol.% Pb. Hot spot problems were eliminated by enhanced adhesion to the substrate. The films geometry was determined by lift-off photolithographic technique. Pinning force densities, estimated from the field dependence of Jc, obey a scaling law. The absolute value of the pinning force density maximum PMAXincreases markedly with decreasing Pb content, up to a maximum around ≈ 50 Vol.% Pb. The self current density is not directly correlated with PMAX. At the lower part of Pb concentration, percolation effects have been observed. Values of ρJcand ρJc²were calculated showing that this system is inferior to existing A-15 materials for use as a superconducting switch material.