The formation of small polaron at the conducting LaAlO₃/SrTiO₃ interface

The interplays among various degrees of freedom such as charge, spin, orbital and lattice generate striking physical properties in oxide heterostructures that are not observed in their parent bulk materials. In this study, via first-principles calculations, we show that the excess electrons at the conducting LaAlO₃/SrTiO₃ (LAO/STO) interface favor the formation of polaron states. These electrons interact strongly with the lowest d_xy orbital of the interfacial Ti lattices, forming localized splitting states. Compared with SrTiO₃ bulk, the formation of the polaron states is more favorable at LAO/STO interface, which is ascribed to the reduced dimensionality and lattice symmetry. These results suggest that some of the excess electrons are localized and do not contribute to the transport effectively, and also shed light on a new direction to understand various novel properties of the conducting LAO/STO interface.