High-pressure study of topological semimetals XCd₂Sb₂ (X = Eu and Yb)

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 XCd_2Sb_2 (X = \rm Eu and Yb), which have the same crystal structure. In antiferromagnetic (AFM) Weyl semimetal EuCd_2Sb_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_2Sb_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_2Sb_2, revealing the robustness of pressure-induced superconductivity against structural instability. Similar structural phase transition may also occur in EuCd_2Sb_2, causing the disappearance of magnetism. Our results show that XCd_2Sb_2 (X = \rm Eu and Yb) is a novel platform for exploring the interplay among magnetism, topology, and superconductivity.