Engineering Gapless Edge States from Antiferromagnetic Chern Homobilayer.

Abstract

We put forward that stacked Chern insulators with opposite chiralities offer a strategy to achieve gapless helical edge states in two dimensions. We employ the square lattice as an example and elucidate that the gapless chiral and helical edge states emerge in the monolayer and antiferromagnetically stacked bilayer, characterized by Chern number <math xmlns="http://www.w3.org/1998/Math/MathML"><mi>C</mi><mo>=</mo><mo>-</mo><mn>1</mn></math> and spin Chern number <math xmlns="http://www.w3.org/1998/Math/MathML"><msub><mrow><mi>C</mi></mrow><mrow><mi>S</mi></mrow></msub><mo>=</mo><mo>-</mo><mn>1</mn></math>, respectively. Particularly, for a topological phase transition to the normal insulator in the stacked bilayer, a band gap closing and reopening procedure takes place accompanied by helical edge states disappearing, where the Chern insulating phase in the monolayer vanishes at the same time. Moreover, EuO is revealed as a suitable candidate for material realization. This work is not only valuable to the research of the quantum anomalous Hall effect but also offers a favorable platform to realize magnetic topologically insulating materials for spintronics applications.