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

TL;DR

This paper theoretically investigates how f-d magnetic exchange interactions in pyrochlore iridates lead to the emergence of topological phases like Weyl semimetals and Axion insulators, highlighting the interplay between localized f-electrons and itinerant d-electrons.

Contribution

It introduces a minimal model for R$_2$Ir$_2$O$_7$ that captures the effects of f-d exchange and Hubbard interactions on topological phases, revealing their cooperative role in stabilizing Weyl semimetals.

Findings

f-d exchange induces Weyl semimetal and Axion insulator phases.

f-d exchange expands the parameter space for Weyl semimetal stability.

Hubbard interaction and f-d exchange cooperate to stabilize topological phases.

Abstract

We study theoretically the effects of f-d magnetic exchange interaction in the R$_2$Ir$_2$O$_7$ pyrochlore iridates. The R$^{3+}$ f-electrons form localized magnetic doublets due to the crystal field environment, while the Ir$^{4+}$ 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 semi-metal 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 semi-metal over a larger region of parameter space than when it is induced by d-electron correlations alone. Applications to experiments are discussed.