Design of Mott and topological phases on buckled 3d-oxide honeycomb lattices

TL;DR

This study systematically explores the electronic and topological phases in (111)-oriented LaXO3/LaAlO3 superlattices, revealing diverse symmetry-breaking phenomena and identifying LaMnO3 as a topological Chern insulator.

Contribution

It provides a comprehensive DFT+U analysis of ground state trends across the 3d transition metal series in buckled honeycomb oxide lattices, uncovering novel symmetry-breaking and topological phases.

Findings

LaMnO3 exhibits a sizable gap due to spin-orbit coupling, indicating a topological Chern insulator phase.

Unanticipated broken symmetry phases emerge from competition between local and global symmetries.

Systematic trends in ground states are established across the 3d transition metal series.

Abstract

Perovskite bilayers with (111)-orientation combine a honeycomb lattice as a key feature with the strongly correlated, multiorbital nature of electrons in transition metal oxides. In a systematic DFT+$U$ study of (111)-oriented (La$X$O$_3$)$_2$/(LaAlO$_3$)$_4$ superlattices, we establish trends in the evolution of ground states versus band filling in (111)-oriented (La$X$O$_3$)$_2$/(LaAlO$_3$)$_4$ superlattices, with $X$ spanning the entire $3d$ transition metal series. The competition between local quasi-cubic and global triangular symmetry triggers unanticipated broken symmetry phases, with mechanisms ranging from Jahn-Teller distortions, to charge-, spin-, and orbital-ordering. LaMnO$_3$, where spin-orbit coupling opens a sizable gap in the Dirac-point Fermi surface, emerges as a topological Chern insulator.