Role of local structural distortions on the origin of j=1/2 pseudo-spin state in sodium iridate

TL;DR

This study reveals that local structural distortions significantly influence the pseudo-spin states in sodium iridate, affecting its electronic properties and insulating behavior through a combination of theoretical and spectroscopic analyses.

Contribution

It demonstrates that local octahedral distortions cause admixture of pseudo-spin states and enhance charge transfer, providing new insights into the origin of the j=1/2 state in sodium iridate.

Findings

Pseudo-spin states have admixture of t2g and eg characters due to distortions.

Local distortions enable Ir 5d- O2p hybridization, affecting insulating properties.

Slater insulator phase is ruled out based on spectroscopic and magnetic data.

Abstract

Na2IrO3 (NIO) is known to be a spin-orbit (SO) driven j=1/2 pseudo-spin Mott-Hubbard (M-H) insulator. However, the microscopic origin of the pseudo-spin state and the role of local structural distortions have not been clearly understood. Using a combination of theoretical calculations and x-ray spectroscopy, we show that the energetics in the vicinity of Fermi level (EF) is governed by SO interactions, electron correlation and local octahedral distortions. Contrary to the earlier understanding, here we show that the j=3/2 and 1/2 pseudo-spin states have admixture of both t2g and eg characters due to local structural distortion. Reduction of local octahedral symmetry also enables Ir 5d- O2p hybridization around the EF resulting in a M-H insulator with enhanced charge transfer character. The possibility of Slater insulator phase is also ruled out by a combination of absence of room temperature DoS in valence band spectra, calculated moments and temperature dependent magnetization measurements.