Emergence of a Novel Pseudogap Metallic State in a Disordered 2D Mott Insulator

We explore the nature of the phases and an unexpected disorder-driven Mott insulator to metal transition in a single crystal of the layered dichalcogenide 1T-TaS2 that is disordered without changing the carrier concentration by Cu intercalation. Angle resolved photoemission spectroscopy measurements reveal that increasing disorder introduces delocalized states within the Mott gap that lead to a finite conductivity, challenging conventional wisdom. Our results not only provide the first experimental realization of a disorder-induced metallic state but in addition also reveal that the metal is a non-Fermi liquid with a pseudogap with a suppressed density of states that persists at finite temperatures. Detailed theoretical analysis of the two-dimensional disordered Hubbard model shows that the novel metal is generated by the interplay of strong interaction and disorder.