Evidence for modification of the superconducting order parameter in YBa/sub 2/Cu/sub 3/O/sub 7-δ/ films by injection of a spin polarized current

Abstract

We have deposited novel bilayer thin films of a ferromagnetic material and YBa/sub 2/Cu/sub 3/O/sub 7/ separated by a thin Au diffusion barrier to study the effects of a spin polarized nonequilibrium quasiparticle population on the superconducting order parameter. Thin films of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//, Au, and Permalloy (Ni/sub 0.8/Fe/sub 0.2/) were deposited by pulsed laser deposition onto (100) MgO, SrTiO/sub 3/, or LaAlO/sub 3/ substrates. A thin stripe of YBa/sub 2/Cu/sub 3/,O/sub 7-/spl delta//, was patterned and two pairs of Au cross stripes for current and voltage contact were deposited at each end. Between these contacts a Permalloy and a Au cross stripe was also deposited to serve as the spin polarized and unpolarized quasiparticle injection sources, respectively. Utilizing this pseudo-three terminal device configuration we have in some samples measured reductions in the superconducting order parameter at the ferromagnet contact as compared to the normal metal contact. Details of this experiment, issues for optimized fabrication, and theoretical issues are discussed.