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

TL;DR

This paper proposes a novel half-metal/insulator superlattice that intrinsically forms a spin-polarized two-dimensional electron gas through quantum well effects, differing from traditional interface-driven 2DEGs, with potential applications in spintronics.

Contribution

It introduces a new mechanism for 2DEG formation in oxide superlattices based on quantum confinement and strong correlations, expanding the design possibilities for spintronic devices.

Findings

A periodic quantum well breaks $t_{2g}$ degeneracy in the superlattice.

The 2DEG forms in the spin-down channel due to quantum confinement.

The superlattice exhibits high spin polarization and orbital polarization.

Abstract

Layered oxide heterostructures are the new routes to tailor desired electronic and magnetic phases emerging from competing interactions involving strong correlation, orbital hopping, tunnelling and lattice coupling phenomena. Here, we propose a half-metal/insulator superlattice that intrinsically forms spin-polarized two-dimensional electron gas (2DEG) following a mechanism very different from the widely reported 2DEG at the single perovskite polar interfaces. From DFT$+U$ study on Sr$_2$FeMoO$_6$/La$_2$CoMnO$_6$ (001) superlattice, we find that a periodic quantum well is created along [001] which breaks the three-fold $t_{2g}$ 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 next generation of oxide heterostructures.