Re-entrant unconventional superconductivity induced by rare-earth substitution in Nd1-xEuxNiO2 thin films

Dung Vu; Hangoo Lee; Daniele Nicoletti; Wenzheng Wei; Zheting Jin; Dmitry V. Chichinadze; Michele Buzzi; Wenxin Li; Xinhao Yang; Rongting Wu; Christopher A. Mizzi; Tiema Qian; Boris Maiorov; Alexey Suslov; Yu He; Cyprian Lewandowski; Sohrab Ismail-Beigi; Frederick Walker; Andrea Cavalleri; Charles Ahn

doi:10.1038/s41467-026-70254-0

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arXiv · 2508.15968

Re-entrant unconventional superconductivity induced by rare-earth substitution in Nd1-xEuxNiO2 thin films

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Abstract

High temperature superconductivity is typically associated with strong coupling and a large superconducting gap, yet these characteristics have not been demonstrated in the nickelates. Here, we provide experimental evidence that Eu substitution in the spacer layer of Nd1-xEuxNiO2 (NENO) thin films enhances the superconducting gap, driving the system toward a strong-coupling regime. This is accompanied by a magnetic-exchange-driven magnetic-field-enhanced superconductivity. We investigate the upper critical magnetic field, Hc2, and superconducting gap of superconducting NENO thin films with x=0.2 to 0.35. Magnetoresistance measurements reveal magnetic-field-enhanced superconductivity in NENO films. We interpret this phenomenon as a result of interaction between magnetic Eu ions and superconducting states in the Ni dx2-y2 orbital. The upper critical magnetic field strongly violates the weak-coupling Pauli limit. Infrared spectroscopy confirms a large gap-to-Tc ratio $2 \Delta k_B T_c \approx 5 - 6$, indicating a stronger coupling pairing mechanism in NENO relative to the Sr-doped NdNiO2. The substitution of Eu in the rare-earth layer provides a method to modify the superconducting gap in Nd-based nickelates, an essential factor in engineering high-Tc superconductivity in infinite-layer nickelates.

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Dung Vu, Hangoo Lee, Daniele Nicoletti, Wenzheng Wei, Zheting Jin, Dmitry V. Chichinadze, Michele Buzzi, Wenxin Li, Xinhao Yang, Rongting Wu, Christopher A. Mizzi, Tiema Qian, Boris Maiorov, Alexey Suslov, Yu He, Cyprian Lewandowski, Sohrab Ismail-Beigi, Frederick Walker, Andrea Cavalleri, Charles Ahn. 2025-08-21. Re-entrant unconventional superconductivity induced by rare-earth substitution in Nd1-xEuxNiO2 thin films. https://doi.org/10.1038/s41467-026-70254-0

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