Direct spectroscopic evidence of charge reversal at the Pb(Zr _0.2Ti_0.8)O₃/La_0.7Sr _0.3MnO₃ heterointerface

At the heterointerface of a top ferroelectric Pb(Zr_0.2Ti _0.8)O₃ (PZT) ultrathin film and a bottom La _0.7Sr_0.3MnO₃ (LSMO) electrode, we used continuous synchrotron-radiation photoelectron spectroscopy to probe in situ and demonstrated that the interfacial charges are reversible and their affected valence-band barrier height becomes modulated upon 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 ultrathin ferroelectric oxide thin film.