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<p>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 Nd<sub>1-<i>x</i></sub>Eu<sub><i>x</i></sub>NiO<sub>2</sub> (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, <i>H</i><sub><i>c2</i></sub>, and the&#xa0;superconducting gap of superconducting NENO thin films with <i>x</i> = 0.2 to 0.35. Magnetoresistance measurements reveal magnetic-field-enhanced superconductivity in NENO films. We interpret this phenomenon as a result of&#xa0;an interaction between magnetic Eu ions and superconducting states in the Ni d<sub>x2-y2</sub> orbital. The upper critical magnetic field strongly violates the weak-coupling Pauli limit. Infrared spectroscopy confirms a large gap-to-<i>T</i><sub><i>c</i></sub> ratio <InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(2\Delta /{k}_{B}{T}_{{\rm{c}}}\simeq 5-6\)</EquationSource> <EquationSource Format="MATHML"><math> <mn>2</mn> <mi mathvariant="normal">Δ</mi> <mo>/</mo> <msub> <mrow> <mi>k</mi> </mrow> <mrow> <mi>B</mi> </mrow> </msub> <msub> <mrow> <mi>T</mi> </mrow> <mrow> <mi mathvariant="normal">c</mi> </mrow> </msub> <mo>≃</mo> <mn>5</mn> <mo>−</mo> <mn>6</mn> </math></EquationSource> </InlineEquation>, indicating a stronger coupling pairing mechanism in NENO relative to the Sr-doped NdNiO<sub>2</sub>. The substitution of Eu in the rare-earth layer causes pronounced modifications of the superconducting gap and magnetic interactions in Nd-based nickelates, opening new pathways to engineer high-<i>T</i><sub><i>c</i></sub> superconductivity in infinite-layer nickelates.</p>

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

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年3月5日

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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 J. Walker,
  • Andrea Cavalleri,
  • Charles H. Ahn

摘要

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 the 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 an 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 \(2\Delta /{k}_{B}{T}_{{\rm{c}}}\simeq 5-6\) 2 Δ / k B T c ≃ 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 causes pronounced modifications of the superconducting gap and magnetic interactions in Nd-based nickelates, opening new pathways to engineer high-Tc superconductivity in infinite-layer nickelates.