Exchange field enhanced upper critical field of the superconductivity in compressed antiferromagnetic EuTe₂

Understanding the interplay between superconductivity and magnetism has been a long-standing challenge in condensed matter physics. Here we report high pressure studies on the C-type antiferromagnetic semiconductor EuTe₂ up to 36.0 GPa. A structural transition from the I4/mcm to the C2/m space group is identified at ~16 GPa. Superconductivity is observed above ~5 GPa in both structures. In the low-pressure phase, magnetoresistance measurements reveal strong couplings between the local moments of Eu²⁺ and the conduction electrons of Te 5p orbits. The upper critical field of superconductivity is well above the Pauli limit. While EuTe₂ becomes nonmagnetic in the high-pressure phase and the upper critical field drops below the Pauli limit. Our results demonstrate that the high upper critical field of EuTe₂ in the low-pressure phase is due to the exchange field compensation effect of Eu²⁺ and the superconductivity in both structures may arise in the framework of the Bardeen-Cooper-Schrieffer theory.

Hualei Sun, Liang Qiu, Yifeng Han, Yunwei Zhang, Weiliang Wang, Chaoxin Huang, Naitian Liu, Mengwu Huo, Lisi Li, Hui Liu, Zengjia Liu, Peng Cheng, Hongxia Zhang, Hongliang Wang, Lijie Hao, Man-Rong Li, Dao-Xin Yao, Yusheng Hou, Pengcheng Dai, Meng Wang