Charge transfer in LaVO3/LaTiO3 multilayers: Strain-controlled dimensionality of interface metallicity between two Mott insulators

We use density-functional theory plus dynamical mean-field theory to demonstrate the emergence of a metallic layer at the interface between the two Mott insulators ${\mathrm{LaTiO}}₃$ and ${\mathrm{LaVO}}₃$. The metallic layer is due to charge transfer across the interface, which alters the valence state of the transition-metal cations close to the interface. Somewhat counterintuitively, the charge is transferred from the Ti cations with formal ${d}¹$ electron configuration to the the V cations with formal ${d}²$ configuration, thereby increasing the occupation difference of the ${t}_2g$ states. This can be understood as a result of a gradual transition of the charge-transfer energy, or electronegativity, across the interface. The spatial extension of the metallic layer, in particular toward the ${\mathrm{LaTiO}}₃$ side, can be controlled by epitaxial strain, with tensile strain leading to a localization within a thickness of only two unit cells. Our results open up a route for creating a tunable quasi-two-dimensional electron gas in materials with strong electronic correlations.