Emergent Novel Metallic State in a Disordered 2D Mott Insulator

It is well established that for non-interacting electrons, increasing disorder drives a metal into a gapless localized Anderson insulator. While in three dimensions a threshold in disorder must be crossed for the transition, in two dimensions and lower, the smallest amount of disorder destabilizes the metal. The nature of the metal-insulator transition in an interacting system remains unresolved. Here we explore the effect of disorder on a strongly correlated Mott insulator without changing the carrier concentration. Angle resolved photoemission spectroscopy (ARPES) measurements on copper intercalated single crystals of the layered dichalcogenide 1T-TaS2 reveal the presence of new delocalized states within the Mott gap. This is the first experimental realization of a novel disorder-induced metal that was theoretically predicted to exist between the Mott insulator and Anderson insulator.