EVIDENCE FOR MODIFICATION OF THE SUPERCONDUCTING ORDER-PARAMETER IN YBA2CU3O7-DELTA FILMS BY INJECTION OF A SPIN-POLARIZED CURRENT

We have deposited novel bilayer thin films of a ferromagnetic material and YBa2Cu3O7 separated by a thin Au diffusion barrier to study the e ffects of a spin polarized nonequilibrium quasiparticle population on the superconducting order parameter, Thin films of YBa2Cu3O7-delta, Au , and permalloy (Ni,,Fe,,) were deposited by pulsed laser deposition o nto (100) MgO, SrTiO3 or LaAlO3 substrates. A thin stripe of YBa2Cu3O7 -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 polariz ed and unpolarized quasiparticle injection sources, respectively. Util izing this pseudo-three terminal device configuration we have in some samples measured reductions in the ferromagnet contact as compared to the normal metal contact. Details of this experiment, issues for optim ized fabrication, and theoretical issues are discussed.