Second-order topological insulator in van der Waals heterostructures of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>CoBr</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:msub><mml:mrow><mml:mi>Pt</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mi>HgSe</mml:mi></mml:mrow><mml:mn>3</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:msub><mml:mrow><mml:mi>CoBr</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math>
Zheng Liu, Yafei Ren, Yulei Han, Qian Niu, Zhenhua Qiao
Abstract
The second-order topological insulator, which has $(d\ensuremath{-}2)$-dimensional topological hinge or corner states, has been observed in three-dimensional materials, but has yet not been observed in a two-dimensional system. In this work we theoretically propose the realization of a second-order topological insulator in the van der Waals heterostructure of ${\mathrm{CoBr}}_{2}/{\mathrm{Pt}}_{2}{\mathrm{HgSe}}_{3}/{\mathrm{CoBr}}_{2}$. ${\mathrm{Pt}}_{2}{\mathrm{HgSe}}_{3}$ is a large gap ${\mathbb{Z}}_{2}$ topological insulator. With an in-plane exchange field from neighboring ${\mathrm{CoBr}}_{2}$, a large global band gap of above 70 meV opens up at the edge. The corner states, which are robust against edge disorders and irregular shapes, are confirmed in the nanoflake. We further show that the second-order topological states can also be realized in the heterostructure of the jacut- ingaite family ${\mathbb{Z}}_{2}$ topological insulators. We believe that our work will be beneficial for the experimental realization of second-order topological insulators in van der Waals layered materials.