Crystal field splitting and correlation effect on the electronic structure of A2IrO3

TL;DR

This study investigates the electronic structure of honeycomb iridates Na2IrO3 and Li2IrO3 using RIXS, revealing small crystal field splitting, support for j_eff physics, and evidence of strong Coulomb interactions, classifying them as spin-orbit Mott insulators.

Contribution

The paper provides detailed RIXS measurements showing small non-cubic crystal field splitting and excitonic effects, supporting the j_eff model and the Mott insulating state in A2IrO3.

Findings

Small crystal field splitting validates j_eff physics.

Evidence of large Coulomb interactions from excitonic enhancement.

Na2IrO3 and Li2IrO3 are spin-orbit Mott insulators.

Abstract

The electronic structure of the honeycomb lattice iridates Na2IrO3 and Li2IrO3 has been investigated using resonant inelastic x-ray scattering (RIXS). Crystal-field split d-d excitations are resolved in the high-resolution RIXS spectra. In particular, the splitting due to non-cubic crystal fields, derived from the splitting of j_eff=3/2 states, is much smaller than the typical spin-orbit energy scale in iridates, validating the applicability of j_eff physics in A2IrO3. We also find excitonic enhancement of the particle-hole excitation gap around 0.4 eV, indicating that the nearest-neighbor Coulomb interaction could be large. These findings suggest that both Na2IrO3 and Li2IrO3 can be described as spin-orbit Mott insulators, similar to the square lattice iridate Sr2IrO4.