Resonant inelastic x-ray scattering spectra in the hyperhoneycomb iridate β−Li2IrO3 : First-principles calculations

Abstract

We studied the electronic structure of the $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ insulator within the density-functional theory using the generalized gradient approximation while taking into account strong Coulomb correlations in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band structure method. The $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ undergoes a pressure-induced structural and magnetic phase transition at ${P}_{c}\phantom{\rule{4pt}{0ex}}\ensuremath{\sim}4$ GPa with symmetry lowering to the monoclinic $C2/c$. The structural phase transition is accompanied by the formation of ${\mathrm{Ir}}_{2}$ dimers on the zigzag chains, with an Ir-Ir distance of $\ensuremath{\sim}2.66$ \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 drastic reconstruction of the RIXS spectral peak at 0.7 eV associated with the structural $Fddd\ensuremath{\rightarrow}C2/c$ phase transition at ${P}_{c}$ can be related to the disappearing of the Coulomb correlations in the high-pressure $C2/c$ phase.