Chin. Phys. B, 2022, Vol. 31(7): 076201    DOI: 10.1088/1674-1056/ac7212
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# High-pressure study of topological semimetals XCd2Sb2 (X = Eu and Yb)

Chuchu Zhu(朱楚楚)1, Hao Su(苏豪)2, Erjian Cheng(程二建)1, Lin Guo(郭琳)1, Binglin Pan(泮炳霖)1, Yeyu Huang(黄烨煜)1, Jiamin Ni(倪佳敏)1, Yanfeng Guo(郭艳峰)2,†, Xiaofan Yang(杨小帆)1,‡, and Shiyan Li(李世燕)1,3,4,§
1 State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200438, China;
2 School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China;
3 Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China;
4 Shanghai Research Center for Quantum Sciences, Shanghai 201315, China
Abstract  Topological materials have aroused great interest in recent years, especially when magnetism is involved. Pressure can effectively tune the topological states and possibly induce superconductivity. Here we report the high-pressure study of topological semimetals $X$Cd$_{2}$Sb$_{2}$ ($X = {\rm Eu}$ and Yb), which have the same crystal structure. In antiferromagnetic (AFM) Weyl semimetal EuCd$_{2}$Sb$_{2}$, the Néel temperature (${T}_{\rm N}$) increases from 7.4 K at ambient pressure to 50.9 K at 14.9 GPa. When pressure is above 14.9 GPa, the AFM peak of resistance disappears, indicating a non-magnetic state. In paramagnetic Dirac semimetal candidate YbCd$_{2}$Sb$_{2}$, pressure-induced superconductivity appears at 1.94 GPa, then ${ T}_{\rm c}$ reaches to a maximum of 1.67 K at 5.22 GPa and drops to zero at about 30 GPa, displaying a dome-shaped temperature-pressure phase diagram. High-pressure x-ray diffraction measurement demonstrates that a crystalline-to-amorphous phase transition occurs at about 16 GPa in YbCd$_{2}$Sb$_{2}$, revealing the robustness of pressure-induced superconductivity against structural instability. Similar structural phase transition may also occur in EuCd$_{2}$Sb$_{2}$, causing the disappearance of magnetism. Our results show that $X$Cd$_{2}$Sb$_{2}$ ($X = {\rm Eu}$ and Yb) is a novel platform for exploring the interplay among magnetism, topology, and superconductivity.
Keywords:  high pressure      topological semimetal      magnetism      superconductivity
Received:  17 April 2022      Revised:  09 May 2022      Accepted manuscript online:  23 May 2022
 PACS: 62.50.-p (High-pressure effects in solids and liquids) 74.62.Fj (Effects of pressure) 75.50.Ee (Antiferromagnetics) 81.40.Rs (Electrical and magnetic properties related to treatment conditions)
Fund: Project supported by the National Natural Science Foundation of China (Grant No. 12174064) and the Shanghai Municipal Science and Technology Major Project (Grant No. 2019SHZDZX01). Yanfeng Guo acknowledges the research fund from the State Key Laboratory of Surface Physics and Department of Physics, Fudan University (Grant No. KF2020_09).
Corresponding Authors:  Yanfeng Guo, Xiaofan Yang, Shiyan Li     E-mail:  guoyf@shanghaitech.edu.cn;yangxiaofan@fudan.edu.cn;shiyan_li@fudan.edu.cn