Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Co(0001) trilayers

Epitaxially grown multilayer systems offer the possibility to study the influence of ferromagnetism on superconductivity in a new and controlled way. In this paper, we explore how the superconducting properties of high quality, epitaxially-grown superconductor/normal-metal/ferromagnet trilayers evolve as a function of the exchange splitting in the ferromagnet, and the thickness of the normal metal layer. We report results for Nb(110)/Au(111)/Co(0001), and make a detailed comparison with earlier results for Nb(110)/Au(111)/Fe(110). We use quantitative FFT analysis to confirm the existence of a long-period (2.1 nm) oscillation in the superconducting transition temperature Tc as a function of the Au-layer thickness tAu, for tAu>2 nm, and highlight an additional short-period (0.76 nm) oscillation for tAu<3 nm in Nb/Au/Co. This short-period oscillation can be explained in terms of a damped RKKY-like oscillation of the spin-polarization in Au. The robustness of the long-period oscillation against the substitution of Co for Fe suggests that it is intrinsic to the Au(111) layer on Nb, and may represent a new form of quantum interference in very clean trilayer systems.Comment: 23 pages, 10 figure

Fabrication of (111)-oriented Ca0.5Sr0.5IrO3/SrTiO3 superlattices; a designed playground for honeycomb physics

We report the fabrication of (111)-oriented superlattice structures with alternating 2m-layers (m = 1, 2, and 3) of Ca0.5Sr0.5IrO3 perovskite and two layers of SrTiO3 perovskite on SrTiO3(111) substrates. In the case of m = 1 bilayer films, the Ir sub-lattice is a buckled honeycomb, where a topological state may be anticipated. The successful growth of superlattice structures on an atomic level along the [111] direction was clearly demonstrated by superlattice reflections in x-ray diffraction patterns and by atomically-resolved transmission electron microscope images. The ground states of the superlattice films were found to be magnetic insulators, which may suggest the importance of electron correlations in Ir perovskites in addition to the much discussed topological effects.Comment: 14 pages, 4 figure

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.Comment: 15 pages, 6 figure