Colossal magnetoresistance and topological phase transition in EuZn2As2

We report electrical transport properties of EuZn2As2 under pressures up to 26 GPa. At ambient pressure, EuZn2As2 exhibits an insulating ground state and a approximate to 200% negative magnetoresistance (MR) at B = 5 T and T = 2 K. For pressures up to similar to 3 GPa, the system becomes more insulating, accompanied by a dramatic enhancement of the MR (B = 5 T and T = 2 K) up to approximate to 14 000%. Further increase of pressure drives EuZn2As2 into a metallic state without significant MR. Resistivity measurements under field reveal ferromagnetic characteristics associated with the metallic ground state in pressurized EuZn2As2, distinct from the antiferromagnetic state realized at ambient pressure. We propose the pressure-induced insulator-metal transition and the colossal MR both originate from transformations of the magnetic ground state that strongly reconstruct the electronic structure. This view is supported by first-principles calculations, which further reveal that while antiferromagnetic EuZn2As2 is a trivial insulator, spin-polarized/ferromagnetic EuZn2As2 is a Weyl metal, indicting that the insulator-metal transition in EuZn2As2 is also a topological phase transition. These pressure- and field-induced topological phase transitions in EuZn2As2 are remarkably similar to behaviors reported in EuCd2As2, suggesting a common origin. Our findings demonstrate that spin-orbit coupling, electronic topology, and particularly the magnetic ground state play key roles in determining the physical properties of Eu-based magnetic topological materials.