Highly confined 2D electron gas in SrTiO$_{3}$/SrRuO$_{3}$ superlattices*

In recent years, experimental advances in the creation of atomically smooth interfaces between complex oxides have made possible the observation of unusual electronic phenomena such as the formation of 2D electron gases confined to the interface between insulating compounds. In this work, we explore an alternative for creating a 2D electron gas in oxide interfaces by means of a (SrTiO$_3$)$_5$/(SrRuO$_3$)$_1$ superlattice. LSDA+U and hybrid functional B1-WC DFT calculations with full relaxation of atomic geometry show the presence of a 2D electron gas, and the system can be described with $U=4$ eV. Electronic correlations thus become important with quantum confinement: the system is a minority spin half metal with a magnetic moment of $\mu=4 \mu_B$. Degenerate Ru 4d$_{(xz,yz)}$ states are the main responsible for the DOS at the Fermi level, whose shape strongly resembles that of 1D free-electron gases. Our results suggest that the material could find uses in spintronic devices.