Competition between Chern and Mott insulating phases in oxide superlattices

Transition metal oxides exhibit a strong interplay of lattice, charge, spin and orbital degrees of freedom which leads to a rich functionality including the tendency to break time reversal symmetry. This makes them attractive candidates to realize Chern insulating phases with some advantages over magnetic doping of Z₂ topological insulators. I will review recent activities in the theoretical prediction of Chern insulators (CI) in oxide superlattices based on density functional theory calculations including an on-site Coulomb term and spin-orbit coupling. A systematic study of superlattices that host a (buckled) honeycomb pattern, derived from the perovskite, (LaXO₃)₂/(LaAlO₃)₄(111) [1,2], or corundum structure, (X₂O₃)₁/(Al₂O₃)₅ (0001) [3,4], with X=3d, 4d or 5d element, reveals several promising candidates. Ferromagnetic coupling and the symmetry of the two honeycomb sublattices turns out to be an essential ingredient. The caveat is that many of those are metastable w.r.t. spontaneous symmetry breaking (e.g. Jahn-Teller effect, charge and/or orbital ordering, antiferromagnetic coupling) and the ground state is often a trivial Mott insulating phase, albeit with magnetic and electronic reconstruction distinct from the reference bulk materials. Strain or non-equilibrium excitations may be auspicious to reach the CI state. Last but not least, taking as an example a rocksalt-derived strained (EuO)₁/(MgO)₃(001) superlattice, a link is established between Chern insulating behavior and enhanced thermoelectric response [5].

[1] D. Doennig, S. Baidya, W.E. Pickett and R. Pentcheva, Phys. Rev. B 93, 165145 (2016).

[2] O. Köksal and R. Pentcheva, Sci. Rep. 9, 17306 (2019).

[3] O. Köksal, S. Baidya and R. Pentcheva, Phys. Rev. B 97, 035126 (2018).

[4] O. Köksal and R. Pentcheva, J. Phys. Chem. Solids 128, 301-309 (2019).

[5] O. Köksal and R. Pentcheva, Phys. Rev. B 103, 045135 (2021).