La-doping effect on spin-orbit coupled Sr2IrO4 probed by x-ray absorption spectroscopy

TL;DR

This study investigates how lanthanum doping affects the electronic and local structure of Sr2IrO4, revealing enhanced spin-orbit interaction and structural regularity that facilitate a transition from insulating to conductive states.

Contribution

It provides new insights into the effects of La doping on spin-orbit coupling and structural distortion in Sr2IrO4, linking these changes to the insulator-to-conductor transition.

Findings

Increased branching ratios indicating stronger spin-orbit interaction.

More regular IrO6 octahedra with La doping.

Transition from Mott insulator to conductive state.

Abstract

Sr2IrO4 was predicted to be an unconventional superconductor upon carrier doping since it highly resembles the high-temperature cuprates. Here, to understand carrier doping effect on spin-orbit coupled Mott insulator Sr2IrO4, the electronic structure and local structure distortion for Sr2-xLaxIrO4 system have been investigated by x-ray absorption spectroscopy (XAS). By comparing the intensity of white-line features at the Ir L2,3 absorption edges, we observe remarkably large branching ratios in La-doped compounds, greater than that of the parent material Sr2IrO4, suggesting a strong spin-orbit interaction (SOI) for Sr2IrO4-based system. Moreover, extended x-ray absorption fine structure (EXAFS) spectra demonstrate more regular IrO6 octahedra, i.e. the weakened crystal electric field (CEF) versus La-doping. By theoretical calculations, the synergistic effect of regular IrO6 octahedra and electron doping is established, which accounts for the transition from a Mott insulator to a conductive state in Sr2-xLaxIrO4-based system.