Experimental Evidence of a Dirac Gap Opening in Carbon-Doped Topological Insulator Bi₂Se₃

Magnetic topological insulators (TIs) are promising candidates for realizing the quantum anomalous Hall effect (QAHE) and advancing the development of next-generation low-energy transistors and electronic devices. Doping Bi₂Se₃ with nano-carbon can introduce magnetic order and open the Dirac gap without introducing extrinsic magnetic impurities. In this work, the C_0.06Bi₂Se₃ single crystal was prepared using the Bridgman method, and their electrical and magnetotransport properties were systematically investigated. Temperature-dependent resistivity and magnetoresistance measurements revealed a magnetic-field-induced metal-insulator-like transition near 152 K. Angle-resolved photoemission spectroscopy (ARPES) detected an energy gap of about 43 meV at the Dirac point, confirming that carbon doping modulates the surface state and opens the gap. Pronounced Shubnikov-de Haas oscillations indicate high carrier mobility in C_0.06Bi₂Se₃. Furthermore, the temperature-dependent Kerr spectra shows that the spin relaxation behavior of C₀.₀₆Bi₂Se₃ differs significantly from that of pure Bi₂Se₃; the relaxation process of spin electrons from the surface state (τ_s) dominates the spin dynamics and exhibits distinct trends around 30 K and 150 K due to the interplay of the Dirac gap and impurity-induced states. These results demonstrate the potential of magnetic topological insulator C_0.06Bi₂Se₃ for novel electronic and spintronic applications.