Modulation of electronic state in copper-intercalated 1T-TaS₂

Intercalation is an effective method to modify physical properties and induce novel electronic states of transition metal dichalcogenide (TMD) materials. However, it is difficult to reveal the microscopic electronic state evolution in the intercalated TMDs. Here we successfully synthesize the copper-intercalated 1T-TaS₂ and characterize the structural and electronic modification combining resistivity measurements, atomic-resolution scanning transmission electron microscopy (ADF-STEM), and scanning tunneling microscopy (STM). The intercalated Cu atom is determined to be directly below the Ta atom and suppresses the commensurate charge density wave (CCDW) phase. Two specific electronic modulations are discovered in the near-commensurate (NC) CDW phase: the electron doping state near the defective star of Davids (SDs) in metallic domains and the spatial evolution of the Mott gap in insulating domains. Both modulations reveal that intercalated Cu atoms act as a medium to enhance the interaction between intralayer SDs, in addition to the general charge transfer effect. It also solidifies the Mott foundation of the insulating gap in pristine samples. The intriguing electronic evolution in Cu-intercalated 1T-TaS₂ will motivate further exploration of novel electronic states in the intercalated TMD materials.