Honeycomb lattice iridate on the verge of Mott-collapse

TL;DR

This paper reports the synthesis of a new honeycomb iridate that exhibits a transition from a Mott insulator to a metallic state due to structural modifications, highlighting a Mott collapse driven by ionic substitution.

Contribution

It demonstrates a novel method to induce Mott collapse in a honeycomb iridate through topochemical ionic substitution, revealing new pathways to control electronic phases.

Findings

Observation of metallic behavior in (La,Na)IrO3

Ir zig-zag chain formation with metal-metal bonding

Evidence of Mott collapse induced by ionic substitution

Abstract

A new honeycomb lattice iridate (La,Na)IrO$_3$ ($\approx$ LaNaIr$_2$O$_6$) is successfully synthesized from the spin-orbit coupled Mott insulator Na$_2$IrO$_3$ by replacing the interlayer Na$^+$ ions with La$^{3+}$ ions. (La,Na)IrO$_3$ shows a finite Sommerfeld term in heat capacity and a $-\ln T$ dependence of resistivity, indicating a realization of a metallic state driven by a Mott collapse. Furthermore, crystal structure analysis reveals the formation of Ir zig-zag chains with metal-metal bonding, increasing kinetic energy resulting in the Mott collapse. This observation would be due to a Mott collapse induced in a $J_{\mathrm{eff}} = 1/2$ spin-orbit coupling Mott insulator with an Ir honeycomb lattice by topochemical control of the ionic configuration.