Direct Spectroscopic Evidence of Charge Reversal at PZT/LSMO Heterointerface

At the heterointerface of a top ferroelectric Pb(Zr$_{0.2}$Ti$_{0.8})$O$_{3}$ (PZT) ultrathin film and a bottom La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ (LSMO) electrode, we used continuous synchrotron radiation photoelectron spectroscopy (SR-PES) to probe \textit{in situ} and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated on switching the polarization in the top layer. By monitoring the core-level shifting of the buried LSMO layer under continuous illumination of synchrotron radiation, we directly observed a temporal screening of polarization induced by the photon-generated carriers in the top PZT layer. This dynamic characterization of the core-level shifting of the buried layer demonstrates an effective method to probe the electric conduction and ferroelectric polarization of an ultra-thin ferroelectric oxide thin film.