Fingerprints of Mott and Slater gaps in the core-level photoemission spectra of antiferromagnetic iridates

Abstract

We present Ir $4f$ core-level hard-x-ray photoemission spectroscopy (HAXPES) experiments conducted across antiferromagnetic (AFM) ordering transition in Ruddlesden-Popper iridates Sr${}_2$IrO${}_4$ and Sr${}_3$Ir${}_2$O${}_7$. The Ir $4f$ spectra exhibit distinct changes between the AFM and paramagnetic (PM) phases, with the spectral difference $I_{\text{PM}}-I_{\text{AFM}}$ showing a contrasting behavior in the two compounds. By employing computational simulations using the local-density approximation combined with the dynamical mean-field theory method, we elucidate that $I_{\text{PM}}-I_{\text{AFM}}$ primary reflects the Slater or Mott-Hubbard character of the AFM insulating state rather than material specific details. This sensitivity to fine low-energy electronic structure arises from the dependence of charge-transfer responses to the sudden creation of a localized core hole on both metal-insulator transitions and long-range AFM ordering. Our result broadens the applications of core-level HAXPES as a tool for characterization of electronic structure.

Main: 11 pages, 8 figures ; SM: 2 pages, 3 figures

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