Testing the validity of the strong spin-orbit-coupling limit for octahedrally coordinated iridates in a model system Sr$_3$CuIrO$_6$

TL;DR

This study investigates the electronic structure of Sr$_3$CuIrO$_6$ and finds that the strong spin-orbit-coupling limit does not hold due to significant crystal field effects, challenging existing theoretical models.

Contribution

It provides experimental and theoretical evidence that crystal field effects significantly alter the expected spin-orbit-coupled states in iridates.

Findings

Ir $t_{2g}$ manifold split into three levels

Large non-cubic crystal field splitting observed

Mixing of $j_{eff}=1/2$ and $j_{eff}=3/2$ states

Abstract

The electronic structure of Sr$_3$CuIrO$_6$, a model system for the 5d Ir ion in an octahedral environment, is studied through a combination of resonant inelastic x-ray scattering (RIXS) and theoretical calculations. RIXS spectra at the Ir L$_3$-edge reveal an Ir $t_{2g}$ manifold that is split into three levels, in contrast to the expectations of the strong spin-orbit-coupling limit. Effective Hamiltonian and $ab inito$ quantum chemistry calculations find a strikingly large non-cubic crystal field splitting comparable to the spin-orbit coupling, which results in a strong mixing of the $j_{\mathsf{eff}}=1/2$ and $j_{\mathsf{eff}}=3/2$ states and modifies the isotropic wavefunctions on which many theoretical models are based.