Formation and observation of a quasi-two-dimensional $d_{xy}$ electron liquid in epitaxially stabilized Sr${}_{2-x}$La${}_x$TiO${}_4$ thin films

Abstract

We report the formation and observation of an electron liquid in Sr${}_{2-x}$La${}_x$TiO${}_4$, the quasi-two-dimensional counterpart of SrTiO${}_3$, through reactive molecular-beam epitaxy and {\it in situ} angle-resolved photoemission spectroscopy. The lowest lying states are found to be comprised of Ti 3$d_{xy}$ orbitals, analogous to the LaAlO${}_3$/SrTiO${}_3$ 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 co-operatively at similar energy scales, which provides a possible mechanism for explaining the low free carrier concentrations observed at various oxide heterostructures such as the LaAlO${}_3$/SrTiO${}_3$ interface.

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