Superconducting and transport properties of YBa2Cu3O7∕La0.7Sr0.3MnO3 bilayers

Abstract

Temperature-dependent resistivity, thermoelectric power, and magnetoresistance (MR) are investigated in YBa2Cu3O7∕La0.7Sr0.3MnO3 (YBCO/LSMO) bilayers with the thickness of YBCO fixed at 150 nm and that of LSMO varying from t=0 to 50 nm. It is found that the onset temperature Tc of the superconducting transition retains at a constant value of 74 K for t<50nm, but reduces to 20 K at t=50nm. In conjunction with the existence of a critical thickness of 50 nm for delocalizing charge carriers in the LSMO layer, we attribute the Tc suppression to the diffusion of spin-polarized carriers from the metallic LSMO to the YBCO layer. Furthermore, we observe a sign reversal of MR with temperature in the YBCO(150 nm)/LSMO(50 nm) bilayer, indicating a competition between a positive MR of YBCO and a negative MR of LSMO.