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

Understanding the interplay between superconductivity and magnetism has been a longstanding challenge in condensed matter physics. Here we report high pressure studies on the C -type antiferromagnetic semiconductor EuTe 2 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 Eu 2+ and the conduction electrons of Te 5 p orbits. The upper critical field of superconductivity is well above the Pauli limit. While EuTe 2 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 EuTe 2 in the low-pressure phase is due to the exchange field compensation effect of Eu 2+ and the superconductivity in both structures may arise in the framework of the Bardeen-Cooper-Schrieffer theory. Understanding the interplay between superconductivity and magnetism has been a longstanding challenge in condensed matter physics. Here, the authors uncover a sensitive coupling between the two within the pressure-tuned phase diagram of EuTe 2 and find that certain magnetic orders can stabilize conventional superconductivity far exceeding the Pauli limit.