Competing electronic ground states in (LaAlO$_{3})_{M}$/(SrTiO$_{3})_{N}$(111) and (LaAlO$_{3})_{M}$/(LaNiO$_{3})_{N}$(111) quantum wells

Complex oxide heterostructures exhibit a broad variability of functional properties and electronic states, not available in the bulk. Beyond the much studied (001)-oriented systems, here we highlight theoretical results on (111) perovskite superlattices with and without a polar discontinuity. Density functional theory calculations including an on-site Coulomb repulsion term (GGA$+U)$ reveal a rich set of competing ground states in (LaAlO$_{3})_{M}$/(SrTiO$_{3})_{N}$(111) [1] and (LaAlO$_{3})_{M}$/(LaNiO$_{3})_{N}$(111) superlattices ranging from spin, orbitally polarized, Dirac point Fermi surface to charge ordered flat band phases. For the bilayer ($N=$2), forming a buckled honeycomb lattice, a Dirac-point Fermi surface is obtained in both cases, while symmetry breaking leads to band gap opening with two inequivalent interfaces. Orbital reconstructions and metal-to-insulator transitions show a pronounced sensitivity on the thickness of the quantum well $N$ and in-plane strain. \\[4pt] [1] D. Doennig, W. E. Pickett, and R. Pentcheva, Phys. Rev. Lett. \textbf{111}, 126804 (2013).