Electronic structure of epitaxial perovskite films in the two-dimensional limit: Role of the surface termination

Abstract

An often-overlooked property of transition metal oxide thin films is their microscopic surface structure and its effect on the electronic properties in the ultrathin limit. Contrary to the expected conservation of the perovskite stacking order in the (001) direction, heteroepitaxially grown SrIrO3 films on TiO2-terminated SrTiO3 are found to exhibit a terminating SrO surface layer. The proposed mechanism for the self-organized conversion involves the adsorption of excess oxygen ions at the apical sites of the IrO2-terminated surface and the subsequent decomposition of the IrO6 octahedra into gaseous molecular IrO3 and the remaining SrO-terminated surface. Whereas the ab initio calculated electronic structure of SrO-terminated SrIrO3 in the monolayer limit exhibits a striking similarity to bulk Sr2IrO4, the broken octahedral symmetry at the IrO2-terminated surface would mix the otherwise crystal field split eg and t2g states, resulting in distinctly different low-energy electronic states.