Electronic structure and x-ray magnetic circular dichroism in the hyperhoneycomb iridate β−Li2IrO3

Abstract

We studied the electronic, magnetic, and optical properties of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ insulator within the density-functional theory using the generalized gradient approximation taking into account strong Coulomb correlations (GGA+$U$) in the framework of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The x-ray absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Ir ${L}_{2,3}$ edges were investigated theoretically from first principles. The calculated results are in good agreement with experimental data. We found that the GGA+$U$ approach with Hubbard ${U}_{\text{eff}}=1.5\phantom{\rule{4pt}{0ex}}\mathrm{eV}$ well describes the optical spectra and XMCD spectra at the Ir ${L}_{2,3}$ edges. We investigated the electronic structure of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ under pressure from first principles. The hyperhoneycomb iridate $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ is on the border of the magnetic ordering with relatively weak Coulomb electron-electron correlations. The $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ undergoes a pressure-induced structural and magnetic phase transitions at ${P}_{c}=4.4$ GPa with symmetry lowering to the monoclinic $C2/c$. The structural phase transition is accompanied by a dimerization of the previously equally long $x/y$ Ir-Ir bonds. We find remarkable nonmagnetic ground states of $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ at ${P}_{c}$, with a concomitant electronic phase transition from a Mott insulator to band insulators. We found that ${J}_{\text{eff}}=1/2$ states are still dominant in the low-energy region in high-pressure monoclinic $C2/c$ structure.