Control of a Two-Dimensional Electron Gas on SrTiO$_3$ (111) by Atomic Oxygen

We report on the formation of a two-dimensional electron gas (2DEG) at the bare surface of (111) oriented SrTiO$_{3}$. Angle resolved photoemission experiments reveal highly itinerant carriers with a 6-fold symmetric Fermi surface and strongly anisotropic effective masses [1]. The electronic structure of the 2DEG is in good agreement with self-consistent tight-binding supercell calculations that incorporate a confinement potential due to surface band bending. Our measurements provide insight into the nontrivial consequences of quantum confinement along the [111] direction which is directly relevant to an understanding of electronic structure at (111) orientated interfaces. We further demonstrate that alternate exposure of the surface to ultraviolet light and atomic oxygen allows tuning of the carrier density and the complete suppression of the 2DEG. [1] S. McKeown Walker et al., Phys. Rev. Lett. 113, 177601 (2014)