Origin of the type-II Weyl state in topological antiferromagnetic YbMnBi2

Recently, there are heavy debates concerning the topological nature of ${\mathrm{YbMnBi}}₂$ being a type-II Weyl semimetal with Mn moments having a canting angle of ${10}^{\mathrm{o}}$ or a Dirac semimetal without canting. In this paper, we systematically study the magnetic and topological properties of ${\mathrm{YbMnBi}}₂$ using density functional theory calculations. Our results unveil that bulk ${\mathrm{YbMnBi}}₂$ is a Dirac semimetal with a collinear antiferromagnetic spin order. By canting the magnetic moments of Mn ions, we surprisingly find that ${\mathrm{YbMnBi}}₂$ enters into the type-II Weyl state with a canting angle of ${2}^{\mathrm{o}}$. As Bi vacancies in Mn-Bi-Mn bonds can produce sizable Dzyaloshinskii-Moriya interactions and thus cant the magnetic moments of Mn ions, we argue that the possible Bi vacancies induce a topological phase transition from a Dirac semimetal to a type-II Weyl semimetal in the realistic ${\mathrm{YbMnBi}}₂$. Our work provides an insight into the realizations of the type-II Weyl state in antiferromagnetic topological materials.