Multiple Magnetic Topological Phases in the van der Waals Crystal Mn(Bi,Sb)Se.

Magnetic topological materials have drawn markedly attention recently due to the strong coupling of their novel topological properties and magnetic configurations. In particular, the MnBiTe/(BiTe) family highlights the researches of multiple magnetic topological materials. Via first-principles calculations, we predict that Mn(Bi, Sb)Se, the close relatives of MnBiTe/(BiTe) family, are topological nontrivival in both antiferromagnetic and ferromagnetic configurations. In the antiferromagnetic ground state, Mn(Bi, Sb)Se are simultaneously topological insulators and axion insulators. Massless Dirac surface states emerge on the surfaces parallel to the axis. In ferromagnetic phases, they are axion insulators. Particularly, when the magnetization direction is along the axis, they are also topological crystalline insulators. Mirror-symmetry-protected gapless surface states exist on the mirror-invariant surfaces. Hence, the behaviors of surface states are strongly dependent on the magnetization directions and surface orientations. Our work provides more opportunities for the study of magnetic topological physics.