Density-functional predicted formation of a spin-orbital entangled two dimensional electron gas (2DEG) at the (100) interface between LaAlO₃ and the strong spin-orbit coupled Sr₂IrO₄ due to polar catastrophe

We show that a 2DEG forms at the (100) interface between LaAlO₃ (LAO) and Sr₂IrO₄ (SIO) due to polar catastrophe, analogous to the well-studied LAO/STO (100) interface. While both constituent materials are insulators, LAO being an ordinary band insulator and SIO being a Mott-Hubbard insulator formed due to the large spin-orbit coupling, the interface is metallic and a host for a novel, spin-orbital entangled 2DEG. An interesting feature is that unlike the LAO/STO interface, where the 2DEG spreads into several monolayers, the 2DEG in the present case is predicted to be sharply localized to more-or-less a single monolayer, occupying the upper J_eff = 1/2 Hubbard band with the electron density being half an electron per interface Ir atom. Unlike the complex sub-band structure in LAO/STO, the interfacial Fermi surface is simple, being square-like. Preliminary calculations indicate that the 2DEG may destroy the AFM state at the interface. Recently, experimenters have been able to grow epitaxial SIO structures, leading to the hope that the predicted 2DEG can be studied experimentally in the near future.