Formation and Observation of a Quasi-Two-Dimensional dxy Electron Liquid in Epitaxially Stabilized Sr2−xLaxTiO4 Thin Films

We report the formation and observation of an electron liquid in Sr2−xLaxTiO4, the quasi-two- dimensional counterpart of SrTiO3, through reactive molecular-beam epitaxy and in situ angle-resolved photoemission spectroscopy. The lowest lying states are found to be comprised of Ti 3dxy orbitals, analogous to the LaAlO3=SrTiO3 interface and exhibit unusually broad features characterized by quantized energy levels and a reduced Luttinger volume. Using model calculations, we explain these characteristics through an interplay of disorder and electron-phonon coupling acting cooperatively at similar energy scales, which provides a possible mechanism for explaining the low free carrier concentrations observed at various oxide heterostructures such as the LaAlO3=SrTiO3 interface.