Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Fe(110) trilayers

In order to clarify the influence of ferromagnetism on superconductivity through a normal metal layer, the superconducting properties of epitaxial Nb(110)/Au(111)/Fe(110) trilayers were studied as a function of the thickness tAu of the intervening Au layer. Structural characterization of the samples revealed sharp interfaces, almost free from roughness. A strong suppression of the superconducting transition temperature Tc was observed for tAu<10 A, implying a strong spin-polarization of the Au layer in the vicinity of the Au/Fe interface. A periodic change of Tc with a period of ~21 A (~9 atomic monolayer of Au) was observed for 20 A<tAu<104 A. Neither the Fermi surface nesting of the normal metal layer, nor Fulde-Ferrel-Larkin-Ovchinnikov oscillations induced by a superconducting proximity effect in the ferromagnet can by themselves account for the observed period. These results suggest that a new and more subtle form of quantum interference occurs in very clean trilayer systems.