Spin-polarized transport across a La 0.7 Sr 0.3 MnO 3 /YBa 2 Cu 3 O 7-x interface: role of Andreev bound states

Transport across an La 0.7 Sr 0.3 MnO 3 /YBa 2 Cu 3 O 7-x (LSMO/YBCO) interface is studied as a function of temperature and surface morphology. For comparison, control measurements are performed in nonmagnetic heterostructures of LaNiO 3 /YBCO and Ag/YBCO. In all cases, YBCO is used as bottom layer to eliminate the channel resistance and to minimize thermal effects. The observed differential conductance reflects the role of Andreev bound states in the a-b plane, and displays the suppression of such states by the spin-polarized transport across the interface. The theoretical analysis of the measured data reveals decay of the spin polarization near the LSMO surface with temperature, consistent with the reported photoemission data.