Magnetism-induced ideal Weyl state in bulk van der Waals crystal MnSb2Te4

We have unveiled a magnetic exchange-induced topological phase transition in a bulk natural van der Waals crystal MnSb2Te4, based on magnetization and magnetotransport measurements and first principles calculations. At the A-type antiferromagnetic ground state, MnSb2Te4 is a topologically trivial insulator with a bandgap of ∼ 42 meV at the Γ point of the Brillouin zone. A small magnetic field less than 1.4 T along the c axis can drive the system into a spin fully polarized state, which hosts only a single pair of Weyl points setting near the Γ point at the Fermi level without other band mixing, supported by both the first principles calculations and the measured anomalous Hall effect. The results would setup an excellent paradigm for the study of interplay between magnetism and nontrivial topology of the electronic band structure.