Resonant inelastic x-ray scattering spectra in the hyperhoneycomb iridate $\beta$-Li$_2$IrO$_3$: First principles calculations

TL;DR

This study combines first-principles calculations and RIXS spectra analysis to investigate pressure-induced structural, magnetic, and electronic phase transitions in the hyperhoneycomb iridate $eta$-Li$_2$IrO$_3$, revealing dimerization effects and correlation collapse.

Contribution

It provides a detailed theoretical analysis of the electronic structure and RIXS spectra across phase transitions in $eta$-Li$_2$IrO$_3$, highlighting the role of dimerization and Coulomb correlation changes.

Findings

Pressure induces structural and magnetic phase transitions at ~4 GPa.

Formation of Ir$_2$ dimers stabilizes molecular orbitals and causes a Mott to band insulator transition.

RIXS spectral features drastically change at the phase transition, indicating correlation collapse.

Abstract

We studied the electronic structure of $\beta$-Li$_2$IrO$_3$ insulator within the density-functional theory using the generalized gradient approximation with taking into account strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The $\beta$-Li$_2$IrO$_3$ undergoes a pressure-induced structural and magnetic phase transitions at $P_c$ $\sim$4 GPa with symmetry lowering to the monoclinic $C2/c$. The structural phase transition is accompanied by the formation of Ir$_2$ dimers on the zigzag chains, with an Ir-Ir distance of $\sim$2.66~\AA, even shorter than that of metallic Ir. The strong dimerization stabilizes the bonding molecular-orbital state, leads to the collapse of the magnetism and opens the energy gap with a concomitant electronic phase transition from a Mott insulator to band insulator. The resonant inelastic x-ray scattering spectra (RIXS) at the Ir $L_3$ edge were investigated theoretically from first principles. The calculated results are in good agreement with the experimental data. We show that the the drastic reconstruction of the RIXS spectral peak at 0.7 eV associated with the structural $Fddd \rightarrow C2/c$ phase transition at $P_c$ can be related to disappearing of the Coulomb correlations in the high-pressure $C2/c$ phase