Orbital-Selective Spin-Orbit Mott Insulator in Fractional Valence Iridate La$_3$Ir$_3$O$_{11}$

TL;DR

This study reveals an orbital-selective Mott insulating state in La$_3$Ir$_3$O$_{11}$ driven by spin-orbit coupling, structural distortions, and electron correlations, advancing understanding of iridate electronic states.

Contribution

It demonstrates the coexistence of orbital-selective Mott transition and band insulator in a fractional valence iridate, combining experimental infrared spectroscopy with theoretical analysis.

Findings

Robust Mott insulating state confirmed by infrared spectroscopy.

Orbital splitting and dimerization lead to selective Mott transition.

Distinct insulating behavior in $J_{eff}=1/2$ and $J_{eff}=3/2$ bands.

Abstract

The combination of strong spin-orbit coupling and Coulomb interactions makes the $5d$ iridates a unique platform for realizing novel correlated electronic states. Here, utilizing infrared spectroscopy, we demonstrate that a robust Mott insulating state persists in the $1/3$-hole self-doped system La$_3$Ir$_3$O$_{11}$, evidenced by the collapse of the Drude response and the emergence of sharp excitations across the Mott gap. Our theoretical calculations reveal that the insulating behavior arises from the cooperative interplay of structural distortions, spin-orbit coupling, and Coulomb interactions. Specifically, octahedral distortion and Ir-Ir dimerization split the $t_{2g}$ orbitals, driving the $J_{\mathrm{eff}} = 1/2$ bands toward half-filling while keeping the $J_{\mathrm{eff}} = 3/2$ bands away from it. Consequently, electron correlations induce an orbital-selective Mott transition in the $J_{\mathrm{eff}} = 1/2$ bands, whereas a band-insulating gap develops in the $J_{\mathrm{eff}} = 3/2$ bands, thereby stabilizing the unconventional insulating state in La$_3$Ir$_3$O$_{11}$. These findings provide new insights into the design and understanding of the insulating ground state of spin-orbit-coupled iridates.