Spin-polarized topological phases in a ferromagnetic Bi2Te3/MnBi2Te4 bilayer tuned by electric and magnetic fields

Applying electric or magnetic fields is widely used to not only create and manipulate topological states but also facilitate their observations in experiments. In this paper, we show by first-principles calculations and topological analysis that the time-reversal (TR) symmetry-broken quantum spin Hall (QSH) phase emerges in a two-dimensional (2D) ferromagnetic ${\mathrm{Bi}}₂{\mathrm{Te}}₃/{\mathrm{MnBi}}₂{\mathrm{Te}}₄$ bilayer. This TR-symmetry broken QSH phase possesses a highly tunable nontrivial band gap under external electric fields (or tuning interlayer distance). Furthermore, based on the Wannier-function-based tight-binding approach, we reveal that a topological phase transition from the TR-symmetry broken QSH phase to the quantum anomalous Hall (QAH) phase occurs with the increase of magnetic fields. Besides, we also find that a reverse electric fields can facilitate the realization of QAH phase. Our paper not only uncovers the ferromagnetic topological properties of ${\mathrm{Bi}}₂{\mathrm{Te}}₃/{\mathrm{MnBi}}₂{\mathrm{Te}}₄$ bilayer tuned by electric and magnetic fields, but also can stimulate further applications to spintronics and topological devices.