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

TL;DR

This study uses core-level photoemission spectroscopy and advanced simulations to distinguish between Slater and Mott-Hubbard insulating states in antiferromagnetic iridates, revealing how magnetic order influences electronic structure.

Contribution

It demonstrates that core-level spectra differences can identify the nature of insulating states, providing a new spectroscopic approach to study correlated electron systems.

Findings

Spectral differences reflect Slater or Mott-Hubbard character.

Charge-transfer responses depend on magnetic and insulating states.

Core-level HAXPES can characterize electronic structure in correlated materials.

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.