Evolution of electronic structure of Ru-doped single-crystal iridiates, Sr$_2$Ir$_{1-x}$Ru$_x$O$_4$

TL;DR

This study explores how Ru doping affects the electronic structure of Sr2IrO4, revealing persistent insulating behavior with weak metallic features and providing insights into doping-dependent properties of 5d iridates.

Contribution

It presents the first detailed optical spectroscopy analysis of Ru-doped Sr2IrO4 across multiple doping levels, highlighting the evolution of electronic structure and charge carrier dynamics.

Findings

All doped samples remain insulating with weak Drude components.

Charge-carrier densities are lower than expected from doping levels.

Electronic structure evolution depends on temperature and doping concentration.

Abstract

We investigated Ru-doped single-crystal 5$d$ iridiates, Sr$_2$Ir$_{1-x}$Ru$_x$O$_{4}$, at three different doping concentrations ($x =$ 0.01, 0.07 and 0.10) using optical spectroscopy. The undoped pristine compound (Sr$_2$IrO$_{4}$) is known as a novel $J_{eff}$ = 1/2 Mott insulator. Remarkably, the optical conductivity spectra of all three samples exhibited the insulating behavior, although we observed weak Drude components in the optical conductivity spectra down to the lowest temperature of 30 K. The charge-carrier densities of the Ru-doped iridiates estimated from the Drude components are significantly smaller than the expected values estimated from the nominal Ru-doping concentrations. Herein, we provide temperature- and doping-dependent electronic structure evolution of Ru-doped iridiates. We expect that our results will be useful for understanding the intriguing Ru-doping-dependent properties of 5$d$ iridiate Sr$_2$IrO$_{4}$.