Honeycomb lattice iridate on the verge of Mott-collapse.

A new honeycomb lattice iridate (La,Na)IrO3(≈LaNaIr2O6) is successfully synthesized from the spin-orbit coupled Mott insulator Na2IrO3by replacing the interlayer Na+ions with La3+ions. (La,Na)IrO3shows a finite Sommerfeld term in heat capacity and a -lnTdependence 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 aJeff= 1/2 spin-orbit coupling Mott insulator with an Ir honeycomb lattice by topochemical control of the ionic configuration.