Detection and Control of the Effective Magnetic Field in a Ca-Doped Bi₂Se₃ Topological Insulator

Topological insulators with surface states are expected to possess perfect spin polarization. Despite the strong potential for spintronic devices, the exact value and gate tuning of spin polarization in topological insulators have not yet been clearly demonstrated. In this research, Ca is doped into the well-established topological material Bi₂Se₃ to enhance the spin-orbit interaction and gate tunability. From the anisotropic magnetoresistance of the Ca-doped Bi₂Se₃ channel, an effective magnetic field of ≈10 T is extracted. Also, the carrier types, i.e., p- and n-channels, as well as the spin polarization are modulated by applying an external gate voltage. This work not only suggests a measurement platform to quantitatively estimate the spin characteristics of a topological insulator but also opens a path to realize gate-controlled pure spin current.