Axion insulator state in ferromagnetically ordered <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Cr</mml:mi><mml:msub><mml:mi mathvariant="normal">I</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:mi mathvariant="normal">B</mml:mi><mml:msub><mml:mi mathvariant="normal">i</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:msub><mml:mi mathvariant="normal">e</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:mi>MnB</mml:mi><mml:msub><mml:mi mathvariant="normal">i</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi mathvariant="normal">S</mml:mi><mml:msub><mml:mi mathvariant="normal">e</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> heterostructures
Yusheng Hou, Jeongwoo Kim, Ruqian Wu
Abstract
Ferromagnetic (FM) axion insulators may greatly simplify experimental explorations of the topological magnetoelectric effect, as the FM ordering can be stable in a broad range of magnetic field. Through density functional theory calculations and four-band model studies, we find that two-dimensional van der Waals FM $\mathrm{Cr}{\mathrm{I}}_{3}$ and $\mathrm{MnB}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{4}$ overlayers induce opposite-sign exchange fields in the topological surface states of $\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ film when they are ferromagnetically ordered. Consequently, the $\mathrm{Cr}{\mathrm{I}}_{3}/\mathrm{B}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{MnB}{\mathrm{i}}_{2}\mathrm{S}{\mathrm{e}}_{4}$ heterostructure is a robust FM axion insulator, according to surface-resolved Berry curvature calculations. Our work opens up opportunities for the design of materials with the topological magnetoelectric effect.