Charge transfer at YBa$_{2}$Cu$_{3}$O$_{7}$/La$_{0.7}$Ca$_{0.3}$MnO$_{3}$ interface*

In this paper, the ferromagnetic (F) /La$_{0.7}$Ca$_{0.3}$MnO$_{3}$/superconducting (S) YBa$_{2}$Cu$_{3}$O$_{7}$ heterostructures of two distinct interfaces with atomically precise interface control have been fabricated to explore the coupling between these two functional layers. A new mechanism of charge transfer in these heterostructures was identified and confirmed by the results of the first principle calculations. This charge transfer, in addition to the previously considered F/S proximate effect, is critical to to the superconductivity and magnetism in these heterostructures. Direct observation of the charge transfer by x-ray absorption spectroscopy is presented. The results from resonant x-ray scattering is likely to be discussed for both type of interfaces.