Complex Orbital State Stabilized by Strong Spin-Orbit Coupling in a Metallic Iridium Oxide IrO$_{2}$

TL;DR

This study uses resonant x-ray diffraction to reveal that strong spin-orbit coupling in metallic IrO$_{2}$ stabilizes complex orbital states similar to those in iridate Mott insulators, with implications for novel electronic phenomena.

Contribution

It demonstrates that ATS scattering can probe complex orbital states in metallic iridates influenced by strong spin-orbit coupling.

Findings

Ir 5$d$ $t_{2g}$ orbitals are close to $J_{eff}$=1/2 state

Resonance behavior differs between $L_3$ and $L_2$ edges

ATS scattering effectively probes orbital states in metals

Abstract

Resonant x-ray diffraction experiments were performed for the metallic iridium oxide IrO$_{2}$. We observed anisotropic tensor of susceptibility (ATS) scattering, the spectrum of which shows a sharp contrast between the $L_{3}$ and $L_{2}$ edges. At the $L_{3}$ edge, resonance excitations were clearly observed from the core 2$p$ orbitals to both the 5$d$ $t_{2g}$ and $e_{g}$ orbitals. In contrast, the resonance mode associated with 5$d$ $t_{2g}$ orbitals was indiscernible at the $L_{2}$ edge. This contrasting behavior indicates that Ir 5$d$ $t_{2g}$ orbitals are fairly close to the $J_{\rm eff}$ = 1/2 state due to the strong spin--orbit coupling in 5$d$ transition metal ions, as in the Mott insulator Sr$_{2}$IrO$_{4}$. Our results clearly demonstrate that ATS scattering is a useful probe for investigating complex orbital states in a metallic state. Such states induce novel phenomena such as the spin Hall effect.