Quantum well structure of a double perovskite superlattice and formation of a spin-polarized two-dimensional electron gas

Abstract

Layered oxide heterostructures are the new route to tailor desired electronic and magnetic phases emerging from competing interactions involving strong correlation, orbital hopping, tunneling, and lattice coupling phenomena. Here, we propose a half-metal/insulator superlattice that intrinsically forms a spin-polarized two-dimensional electron gas (2DEG) following a mechanism very different from the widely reported 2DEG at the single perovskite polar interfaces. From a density functional theory plus $U$ study on a ${\mathrm{Sr}}_{2}{\mathrm{FeMoO}}_{6}/{\mathrm{La}}_{2}{\mathrm{CoMnO}}_{6}$ (001) superlattice, we find that a periodic quantum well is created along [001] which breaks the threefold ${t}_{2g}$ degeneracy to separate the doubly degenerate $xz$ and $yz$ states from the planar $xy$ state. In the spin-down channel, the dual effect of quantum confinement and strong correlation localizes the degenerate states, whereas the dispersive $xy$ state forms the 2DEG, which is robust against perturbations to the superlattice symmetry. The spin-up channel retains the bulk insulating. Both spin polarization and orbital polarization make the superlattice ideal for spintronic and orbitronic applications. The suggested 2DEG mechanism widens the scope of fabricating the next generation of oxide heterostructures.