Current injection into high temperature superconductors: Does spin matter?

Recent comparative studies of quasiparticle injection from colossal magnetoresistance (CMR) materials and normal metals into high transition temperature superconductors (HTS) have led several investigators to conclude that spin-polarized injection from CMR electrodes is far more efficient than ordinary injection in suppressing superconductivity. On the other hand, some ordinary quasiparticle injection experiments have shown greater suppression of superconductivity than was claimed in any of the published spin-injection experiments. Careful analysis and numerical simulations lead us to argue that all spin-injection experiments to date have been hampered by inadequate control samples and that the reported results can be explained by ordinary (unpolarized) quasiparticle injection or simple current summation. We conclude that there is no conclusive evidence that spin-polarized injection into HTS behaves differently from ordinary quasiparticle injection and we discuss criteria for future experiments that could differentiate between the two types of injection. (C) 2001 American Institute of Physics.