Thin Films*

Two-dimensional transition metal oxides (2DTMOs) are a promising addition to the growing array of functional 2D materials, with potential applications related to their long-lived, strongly bound excitons. 2DTMOs are expected to be unusually stable since they do not react with water or oxygen species. However, unlike many other 2D materials, 2DTMOs do not naturally occur in stackable van der Waals-bonded layers, so they present challenges for structural prediction and characterization. Recent experimental work on the MgO(001) surface has demonstrated the growth of thin films of Mg₂TiO₄, whose low energy electronic states are dominated by Ti and O orbitals. We review the structure of these thin films and report on many-body calculations of their electronic excitations. We show density functional theory results on band alignment and the spatial locality of band-edge wavefunctions that demonstrate the viability of long-lived interlayer excitons, and that those results are preserved upon the consideration of electronic correlations. We also report on the quasiparticle properties, absorption spectrum, and excitonic binding energy of bulk Mg₂TiO₄.