Electric and magnetic fields tuned spin-polarized topological phases in two-dimensional ferromagnetic MnBi$_4$Te$_7$

TL;DR

This study demonstrates how electric and magnetic fields can induce and control topological phases in a ferromagnetic MnBi4Te7 monolayer, revealing potential for spintronics and topological device applications.

Contribution

It uncovers the electric and magnetic field-tuned topological phases in MnBi4Te7 monolayers, including the transition from quantum spin Hall to quantum anomalous Hall states.

Findings

TR-symmetry broken QSH phase in MnBi4Te7 monolayer

Electric fields tune the nontrivial band gap

Magnetic fields induce phase transition to QAH state

Abstract

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 work, we show by first-principles calculations and topological analysis that the time-reversal (TR) symmetry-broken quantum spin Hall (QSH) state emerges in a two-dimensional ferromagnetic MnBi$_4$Te$_7$ monolayer. This TR-symmetry broken QSH phase possesses a highly tunable nontrivial band gap under an external electric field (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 work not only uncovers the ferromagnetic topological properties the MnBi$_4$Te$_7$ monolayer tuned by electric and magnetic fields, but also can stimulate further applications to spintronics and topological devices.