The layered crystal of EuSn2As2 has a Bi2Te3-type structure in rhombohedral (R3ˉm) symmetry and has been confirmed to be an intrinsic magnetic topological insulator at ambient conditions. Combining {\it ab initio} calculations and \emph{in-situ} x-ray diffraction measurements, we identify a new monoclinic EuSn2As2 structure in C2/m symmetry above ∼14 GPa. It has a three-dimensional network made up of honeycomb-like Sn sheets and zigzag As chains, transformed from the layered EuSn2As2 via a two-stage reconstruction mechanism with the connecting of Sn-Sn and As-As atoms successively between the buckled SnAs layers. Its dynamic structural stability has been verified by phonon mode analysis. Electrical resistance measurements reveal an insulator-metal-superconductor transition at low temperature around 5 and 15 GPa, respectively, according to the structural conversion, and the superconductivity with a \textit{T}C value of ∼4 K is observed up to 30.8 GPa. These results establish a high-pressure EuSn2As2 phase with intriguing structural and electronic properties and expand our understandings about the layered magnetic topological insulators.
@article{arxiv.2102.00437,
title = {Monoclinic EuSn$_2$As$_2$: A Novel High-Pressure Network Structure},
author = {Lin Zhao and Changjiang Yi and Chang-Tian Wang and Zhenhua Chi and Yunyu Yin and Xiaoli Ma and Jianhong Dai and Pengtao Yang and Binbin Yue and Jinguang Cheng and Fang Hong and Jian-Tao Wang and Yonghao Han and Youguo Shi and Xiaohui Yu},
journal= {arXiv preprint arXiv:2102.00437},
year = {2021}
}