Proximity effect in Nb/Zr multilayers with variable Nb/Zr ratio

We have investigated the effect of varying the individual layer thickness on the superconducting transition temperature (TC) of Nb/Zr multilayers. These thin film multilayer structures were deposited using UHV magnetron sputtering with layer thickness ranging from 0.5 to 8 nm. In conformity with the predictions of the de Gennes equations in the Cooper limit (layer thickness small compared to coherence length), we find that the TC increases with increasing thickness of the Nb layer (when the Zr layer thickness is constant), and decreases with increasing thickness of the Zr layer (when the Nb layer thickness is constant). The possible effect of the existence of an interfacial Nb–Zr layer is discussed. We also point out the marked influence of the in-plane grain dimension on the TC in these multilayers.