Colossal magnetoresistance and topological phase transition in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>EuZn</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>As</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Shuaishuai Luo, Yongkang Xu, Feng Du, Lin Yang, Yuxin Chen, Chao Cao, Yu Song, Huiqiu Yuan
Abstract
We report electrical transport properties of ${\mathrm{EuZn}}_{2}{\mathrm{As}}_{2}$ under pressures up to 26 GPa. At ambient pressure, ${\mathrm{EuZn}}_{2}{\mathrm{As}}_{2}$ exhibits an insulating ground state and a $\ensuremath{\approx}200%$ negative magnetoresistance (MR) at $B=5$ T and $T=2$ K. For pressures up to $\ensuremath{\sim}3$ GPa, the system becomes more insulating, accompanied by a dramatic enhancement of the MR $(B=5 \mathrm{T} \text{and} T=2 \mathrm{K})$ up to $\ensuremath{\approx}14\phantom{\rule{0.16em}{0ex}}000%$. Further increase of pressure drives ${\mathrm{EuZn}}_{2}{\mathrm{As}}_{2}$ into a metallic state without significant MR. Resistivity measurements under field reveal ferromagnetic characteristics associated with the metallic ground state in pressurized ${\mathrm{EuZn}}_{2}{\mathrm{As}}_{2}$, 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 ${\mathrm{EuZn}}_{2}{\mathrm{As}}_{2}$ is a trivial insulator, spin-polarized/ferromagnetic ${\mathrm{EuZn}}_{2}{\mathrm{As}}_{2}$ is a Weyl metal, indicting that the insulator-metal transition in ${\mathrm{EuZn}}_{2}{\mathrm{As}}_{2}$ is also a topological phase transition. These pressure- and field-induced topological phase transitions in ${\mathrm{EuZn}}_{2}{\mathrm{As}}_{2}$ are remarkably similar to behaviors reported in ${\mathrm{EuCd}}_{2}{\mathrm{As}}_{2}$, 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.