Competing exotic topological insulator phases in transition-metal oxides on the pyrochlore lattice with distortion

Abstract

In this work we investigate the phase diagram of heavy (4d and 5d) transition metal oxides on the pyrochlore lattice, such as those of the form $\mathrm{A_2M_2O_7}$, where A is a rare earth element and M is a transition metal element. We focus on the competition between Coulomb interaction, spin-orbit coupling, and lattice distortion when these energy scales are comparable. Strong spin-orbit coupling entangles the spin and the $t_{2g}$ $d$-orbitals giving rise to doublet $j=1/2$ and quadruplet $j=3/2$ states. In contrast to previous works which focused on the doublet manifold, we also discuss the quadruplet manifold which is relevant for several pyrochlore oxides. The Coulomb interaction is taken into account by use of the slave-rotor mean field theory and different classes of lattice distortions which further split the levels of the quadruplet $j=3/2$ manifold are studied. Various topological phases are predicted, including exotic strong and weak topological Mott insulating phases. We discuss the general structure of the phase diagram for several values of $d$-shell filling and various symmetry classes of lattice distortions. Our results are relevant to the search for exotic topological insulators and quantum spin liquids in strongly correlated materials with strong spin-orbit coupling.