Switchable photovoltaic response in hexagonal LuMnO3 single crystals

Hexagonal manganites, such as h-LuMnO₃, are ferroelectric with its polar axis along the hexagonal axis and have a narrow electronic bandgap (≈1.5 eV). Using Pt electrodes, h-LuMnO₃ single crystals display a strong rectification, characteristic of a Schottky diode, and a large photoresponse. It is found that the short circuit photocurrent density J_sc along the polar axis is modulated (up to 25%) by the direction of the ferroelectric polarization P, leading to a short circuit photocurrent loop that mimics the ferroelectric polarization. However, a non-switchable J_sc persists. Diffusion photocurrent is shown to dominate current-in-plane measurements and contributes to the non-switchable J_sc. This observation illustrates the dramatic role of the large optical absorption in hexagonal manganites. The accompanying optical dichroism might challenge disentangling a genuine bulk photovoltaic response in h-LuMnO₃ single crystals, contributing to the non-switchable J_sc. Epitaxial thin films may offer a suitable alternative.