Visible-Light-Engineered Local Bandgap across inhomogeneous ferroelectric interface
Jing Wang (Department of Physics, Beijing Normal University, 100875, Beijing, China)

We report local bandgap engineering via visible light excitation across the inhomogeneous ferroelectric interface based on a point-contact geometry. A reversible photovoltaic effect with a large photocurrent density has been achieved by controlling the polarization directions. The optical absorption from the point-contact inhomogeneous interface shows a redshift (~0.3 eV) with respect to a homogenous capacitor. A combination of first-principle calculations, phase-field simulations and fitting of electron energy loss spectroscopy (EELS) reveals the origin of the bandgap drop: the controllable local strain of ferroelectric thin films (e.g. BiFeO3, Pb(Zr,Ti)O3) underneath the transparent probe, which assisted the efficient separation of charges and holes across the interface. This reversible local bandgap tuning in complex oxides demonstrates a framework to understand the optical behavior affected by order parameters such as electron, orbital and lattice, which may provide us a new platform to integrate the possible applications of controllable photo-emission, photo-voltaic, photo-catalyst devices in the visible light region.