  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.
