Quasiparticle-injection effects in YBa_(2)Cu_(3)O_(7-δ)/La_(1/3)Ca_(2/3)MnO_(3)/La_(2/3)Ca_(1/3)MnO_(3) heterostructures

摘要

We have grown YBa_(2)Cu_(3)O_(7-δ) (40 nm)/La_(1/3)Ca_(2/3)MnO_(3) (2 nm)/La_(2/3)Ca_(1/3)MnO_(3) (30 nm) junctions for quasiparticle-injection measurements. Ferromagnetic (F), antiferromagnetic (AF), and superconducting (S) thin films were sequentially grown "in situ" using a dc-sputtering technique at 850℃ in pure oxygen at pressures around 3.5 mbar. The temperature dependence of the resistivity of the junction, without any current injection, presented coexistence between magnetism and superconductivity with a metallic insulating transition at 186 K, and zero resistance at 52 K. When current was injected from the F layer into the S layer, superconductivity suppression was obtained at temperatures below 52 K; furthermore, small values of current injection were necessary to change the electrical behavior up to the critical temperature. A negative current gain (G) has been observed and described by the relation G∝ατ_(eff), where τ_(eff) is the relaxation time of the quasiparticle. The use of an AF layer as an insulating barrier is also discussed.