Bulk nature of layered perovskite iridates beyond the Mott scenario: An approach from a bulk-sensitive photoemission study

Abstract

We present genuine bulk Ir $5d$ ${j}_{\mathrm{eff}}$ states of layered perovskite iridates obtained by hard-x-ray photoemission spectroscopy (HAXPES) with $s$- and $p$-polarized lights. HAXPES spectra of Sr${}_{2}$IrO${}_{4}$ and Ba${}_{2}$IrO${}_{4}$ are well reproduced by the quasiparticle density of states calculated by the local density approximation with dynamical mean-field theory ($\text{LDA}+\text{DMFT}$). It is demonstrated that the insulating nature of the iridates is triggered by antiferromagnetic correlation (Slater type) combined with electron correlation (Mott type). The extremely-low-energy bulk-sensitive photoemission spectroscopy reveals ``bad metallic'' states in the paramagnetic phase of the iridates, suggesting strongly renormalized metallic states above the N\'eel temperature as predicted by the $\text{LDA}+\text{DMFT}$.