Metamagnetic quantum criticality in the antiferromagnetic topological insulator MnBi₂Te₄

Combining transport and magnetization measurements, we discover the emergence of a tricritical point connecting the antiferromagnetic, metamagnetic, and paramagnetic regions in MnBi₂Te₄, a magnetic topological insulator candidate which can potentially exhibit axion electrodynamics. We observe a unique magnetic field-driven phase diagram where the second-order antiferromagnetic to paramagnetic phase boundary bifurcates into two first-order lines at the tricritical point. The two first-order lines enclosing the metamagnetic phase eventually

terminate at the quantum critical endpoints with the application of magnetic field.