A Combined Theoretical and Experimental Investigation on an Fe-Doped Bi ₂ Se ₃ Topological Insulator

Research on magnetic ion doping in topological insulators (TIs) such as Bi2Se3 is rapidly advancing due to its technological potential and relevance to fundamental physics. In this study, a detailed investigation has been carried out on an Fe-doped Bi2Se3 system through ab initio density functional theory (DFT) calculation and X-ray absorption spectroscopy (XAS) and angle-resolved photoelectron spectroscopy (ARPES) measurements on Fe-doped Bi2Se3 single crystals. Formation energy calculations indicate that Fe preferentially occupies interstitial sites in the van der Waals gap, a finding supported by the XAS and ARPES measurements. The simulated electronic band structure reveals that interstitial Fe doping preserves the bandgap of pristine Bi2Se3, while substitutional doping at Bi sites reduces it. The presence of Se vacancies in the system, as obtained from DFT simulations, has also been corroborated by XAS measurements. Thus, the above combined theoretical and experimental investigations have offered significant insight into a transition metal-doped TI system, which is important for both technological applications and exploration of exotic fundamental physical phenomena.