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Nature, Published online: 20 June 2023; doi:10.1038/d41586-023-01921-1

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Chemical carrier doping of an x-LiPc molecular Mott insulator (Pc=phthalocyanine) induced an insulator–metal transition, and the obtained metallic x-LiPcI reverted to the pristine x-LiPc Mott insulator through dedoping iodine. The advent of the reversible insulator–metal transition by doping and dedoping of the molecular Mott insulator could lead to a new class of strongly correlated materials.

Abstract

The chemical carrier doping of molecular Mott insulators has been poorly investigated to date due to its difficulty. In this study, iodine doping of a molecular Mott insulator, lithium phthalocyanine crystallized in the x-form (x-LiPc), was performed to obtain metallic x-LiPcI. Crystal structure analysis revealed that iodine atoms penetrated channels of x-LiPc and formed one-dimensional chains. The Raman spectroscopy of x-LiPcI indicated the existence of linear I₅ ⁻, demonstrating a transition from a half-filled band of the Mott insulating state to a 2/5-filled band of the metallic state. Electrical resistivity measurements confirmed the metallic nature of x-LiPcI, whereas a thermally activated behavior was observed for pristine x-LiPc. Furthermore, the x-LiPc Mott insulator was reproduced by dedoping iodine from x-LiPcI, suggesting that the electronic state can be reversibly tuned between the Mott insulating and metallic states by chemical doping and dedoping.

Abstract