Topological magnetic phase in LaMnO$_3$ (111) bilayer

TL;DR

This study investigates the topological magnetic phase in LaMnO3 (111) bilayer using first-principles calculations, revealing a transition from semi-metal to topological insulator influenced by lattice distortions and Hubbard interactions.

Contribution

It provides the first detailed analysis of the topological magnetic phase in LaMnO3 (111) bilayer, highlighting the effects of lattice distortion and electron correlations on topological properties.

Findings

Dirac point at Fermi energy in ideal structure

Spin-orbit coupling opens a topological gap

Lattice distortion suppresses topological phase

Abstract

Candidates for correlated topological insulators, originated from the spin-orbit coupling as well as Hubbard type correlation, are expected in the ($111$) bilayer of perovskite-structural transition-metal oxides. Based on the first-principles calculation and tight-binding model, the electronic structure of a LaMnO$_3$ ($111$) bilayer sandwiched in LaScO$_3$ barriers has been investigated. For the ideal undistorted perovskite structure, the Fermi energy of LaMnO$_3$ ($111$) bilayer just stays at the Dirac point, rendering a semi-metal (graphene-like) which is also a half-metal (different from graphene nor previous studied LaNiO$_3$ ($111$) bilayer). The Dirac cone can be opened by the spin-orbit coupling, giving rise to nontrivial topological bands corresponding to the (quantized) anomalous Hall effect. For the realistic orthorhombic distorted lattice, the Dirac point moves with increasing Hubbard repulsion (or equivalent Jahn-Teller distortion). Finally, a Mott gap opens, establishing a phase boundary between the Mott insulator and topological magnetic insulator. Our calculation finds that the gap opened by spin-orbit coupling is much smaller in the orthorhombic distorted lattice ($\sim$$1.7$ meV) than the undistorted one ($\sim$$11$ meV). Therefore, to suppress the lattice distortion can be helpful to enhance the robustness of topological phase in perovskite ($111$) bilayers.