Structural defects and electronic properties of the Cu-doped topological insulator Bi₂Se₃

Motivated by the occurrence of superconductivity transition in Cu-doped topological insulator Bi₂Se₃, we perform a combined study of low temperature scanning tunneling microscopy/spectroscopy and angle-resolved photoemission spectroscopy experiments and of ab initio density functional theory to clarify the doping nature of Cu atoms in Bi₂Se₃ films. By measuring the structural and electronic properties of the Cu-doped Bi₂Se₃ films at different doping temperatures, we find that Cu atoms behave as donors at intercalated and interstitial sites in Bi ₂Se₃ films. Only the interstitial defect density plays an important role in the observation of Landau quantization of the topological surface states in Bi₂Se₃.