paper

Lattice distortion effects on topological phases in (LaNiO)/(LaAlO) heterostructures grown along the [111] direction

arXiv:1306.1002 · doi:10.1103/PhysRevB.88.115146

Abstract

We theoretically investigate the influence of internal and external strain on topological phases in (LaNiO)/(LaAlO) heterostructures grown along the [111] direction. At the Hartree-Fock level, topological phases originate from an interaction-generated effective spin-orbit coupling that opens a gap in the band structure. For the unstrained system, there is a quadratic band touching at the point at the Fermi energy for unpolarized electrons and Dirac points at K, K at the Fermi energy for fully polarized electrons. Using density functional theory we show that the quadratic band touching and Dirac points are remarkably stable to internal strain-induced out-of-plane distortions and rotations of the oxygen octahedra, which we compute. The lack of a gap opening from internal strain implies a robustness to the mean-field predicted topological phases for both the polarized and unpolarized systems. We also consider an external strain imposed along the [001] cubic direction and show this can open a gap at the point but leaves the Dirac points intact. Finally, we compute a phase diagram for parameters relevant to LaNiO which shows that strain favors a phase with polarized orbitals and antiferromagnetic spin order, but leaves earlier predictions for a zero-magnetic field topological quantum Hall state essentially unchanged. Taken together, our results suggest that the [111] growth direction in perovskites may lead to thin films that are relatively immune to distortion effects compared to those grown along [001].

10 pages, 9 figures; published version

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