Magnetic orders and topological phases from f-d exchange in pyrochlore iridates

We study theoretically the effects of f-d magnetic exchange interaction in the R2Ir2O7 pyrochlore iridates. The R3+ f electrons form localized Kramers or non-Kramers doublets, while the Ir4+ d electrons are more itinerant and feel a strong spin-orbit coupling. We construct and analyze a minimal model capturing this physics, treating the Ir subsystem using a Hubbard-type model. First neglecting the Hubbard interaction, we find Weyl semimetal and Axion insulator phases induced by the f-d exchange. Next, we find that f-d exchange can cooperate with the Hubbard interaction to stabilize the Weyl semimetal over a larger region of parameter space than when it is induced by d-electron correlations alone. Applications to experiments are discussed. DOI: 10.1103/PhysRevB.86.235129