High-resolution resonant inelastic x-ray scattering study of the electron-phonon coupling in honeycomb $\alpha$-Li$_2$IrO$_3$

TL;DR

This study uses high-resolution RIXS to reveal strong electron-phonon coupling in honeycomb $ ext{Li}_2 ext{IrO}_3$, showing multi-phonon excitations and phonon-dressed orbital excitations, comparable to 3d transition metal oxides.

Contribution

It provides the first quantitative analysis of electron-phonon coupling in honeycomb $ ext{Li}_2 ext{IrO}_3$ using high-resolution RIXS, demonstrating its significance in 5d systems.

Findings

Observation of a ladder of multi-phonon excitations.

Orbital excitations are dressed by phonons.

Electron-phonon coupling magnitude comparable to 3d transition metal oxides.

Abstract

The excitations in honeycomb $\alpha$-Li$_2$IrO$_3$ have been investigated with high-resolution resonant inelastic x-ray scattering (RIXS) at the O K edge. The low-energy response is dominated by a fully resolved ladder of excitations, which we interpret as being due to multi-phonon processes in the presence of strong electron-phonon coupling (EPC). At higher energies, the orbital excitations are shown to be dressed by phonons. The high quality of the data permits a quantitative test of the analytical model for the RIXS cross-section, which has been proposed to describe EPC in transition metal oxides (TMOs). We find that the magnitude of the EPC is comparable to that found for a range of 3d TMOs. This indicates that EPC may be of equal importance in determining the phenomenology displayed by corresponding 5d based systems.