Topological states in pyrochlore iridates: long-range anisotropy strongly competing with spin-orbit interaction

TL;DR

This study investigates how long-range lattice anisotropies, rather than local distortions, influence the topological states in pyrochlore iridates, highlighting the importance of anisotropic effects over local cage distortions.

Contribution

It demonstrates that long-range anisotropies, not local IrO6 distortions, are key in determining the topological phases in pyrochlore iridates, supported by experimental and ab initio calculations.

Findings

Long-range lattice anisotropies break local cubic symmetry.

IrO6 distortions are not the primary cause of spin-orbit quenching.

Anisotropies strongly influence the topological ground state.

Abstract

In the search for topological phases in correlated electron systems, iridium-based pyrochlores A2Ir2O7 -- materials with 5d transition-metal ions -- provide fertile grounds. Several novel topological states have been predicted but the actual realization of such states is believed to critically depend on the strength of local potentials arising from distortions of IrO6-cages. We test this hypothesis by measuring with resonant x-ray scattering the electronic level splittings in the A= Y, Eu systems, which we show to agree very well with ab initio electronic structure calculations. We find, however, that not distortions of IrO6-octahedra are the primary source for quenching the spin-orbit interaction, but strong long-range lattice anisotropies, which inevitably break the local cubic symmetry and will thereby be decisive in determining the system's topological ground state.