Metal-induced charge transfer, structural distortion, and orbital order in SrTiO${}_{3}$ thin films

Metal-induced charge transfer, structural distortion, and orbital order in SrTiO $_{3}$ thin films

Jaekwang Lee, Chungwei Lin, and Alexander A. Demkov

Phys. Rev. B 87, 165103 – Published 3 April 2013

Abstract

The atomic and electronic properties of the Cs/SrTiO $_{3}$ heterostructure are investigated using density functional theory. Our results suggest that an antiferrodistortive (AFD) or a ferroelectric (FE) like distortion could be induced in SrTiO $_{3}$ (STO) by a Cs layer, depending on the interface bonding geometry between the metal and the oxide. Furthermore, while the AFD distortion extends throughout the STO region, the FE-like distortion decays within two layers of STO. Independent of the interface geometry, we find a large $e_{g}$ orbital splitting (orbital order) around the interface, leading to an $e_{g}$ -based two-dimensional electron gas (2DEG) confined within the two layers of STO, which is fundamentally different from the conventional $t_{2 g}$ -based 2DEG in this material. This unique feature can be understood in terms of the local orbital mixing at the interface. We discuss the relation between the orbital order and structural distortion.