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<p>Recent studies have demonstrated ambient pressure superconductivity in compressively strained La<sub>3</sub>Ni<sub>2</sub>O<sub>7</sub> thin films, yet the phase diagram of heterovalent doping—critical for advancing the field—remains underexplored. Here we report superconductivity in Sr<sup>2+</sup>-doped La<sub>3–<i>x</i></sub>Sr<sub><i>x</i></sub>Ni<sub>2</sub>O<sub>7</sub> films. The superconducting transition temperature (<i>T</i><sub>c</sub>) follows an incomplete dome-like profile, maintaining similar <i>T</i><sub>c</sub> values across a wide doping range (0 ≤ <i>x</i> ≤ 0.21) before diminishing near <i>x</i> ≈ 0.38. Optimally doped films achieve a <i>T</i><sub>c</sub> value of ~42 K, with a high critical current (<i>J</i><sub>c</sub> &gt; 1.4 kA cm<sup>−2</sup> at 2 K) and upper critical fields (<i>μ</i><sub>0</sub><i>H</i><sub>c,∥</sub>(0) = 83.7 T, <i>μ</i><sub>0</sub><i>H</i><sub>c,⟂</sub>(0) = 110.3 T). Scanning transmission electron microscopy reveals that oxygen vacancies predominantly occupy planar NiO<sub>2</sub> sites—unlike apical-site vacancies in bulk samples—due to compressive strain. Additionally, the elongated out-of-plane Ni–O bonds, exceeding those in pressurized bulk samples by 4%, likely weaken the interlayer <InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="41563_2025_2327_Article_IEq1.gif" Format="GIF" Height="18" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="TEX">\({d}_{{z}^{2}}\)</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mrow> <mi>d</mi> </mrow> <mrow> <msup> <mrow> <mi>z</mi> </mrow> <mrow> <mn>2</mn> </mrow> </msup> </mrow> </msub> </math></EquationSource> </InlineEquation> coupling and contribute to the reduced <i>T</i><sub>c</sub> in strained films.</p>

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Superconductivity in Sr-doped La3Ni2O7 thin films

  • 期刊论文

  • 发表日期：

    2025年8月18日

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  • Bo Hao,
  • Maosen Wang,
  • Wenjie Sun,
  • Yang Yang,
  • Zhangwen Mao,
  • Shengjun Yan,
  • Haoying Sun,
  • Hongyi Zhang,
  • Lu Han,
  • Zhengbin Gu,
  • Jian Zhou,
  • Dianxiang Ji,
  • Yuefeng Nie

摘要

Recent studies have demonstrated ambient pressure superconductivity in compressively strained La3Ni2O7 thin films, yet the phase diagram of heterovalent doping—critical for advancing the field—remains underexplored. Here we report superconductivity in Sr2+-doped La3–xSrxNi2O7 films. The superconducting transition temperature (Tc) follows an incomplete dome-like profile, maintaining similar Tc values across a wide doping range (0 ≤ x ≤ 0.21) before diminishing near x ≈ 0.38. Optimally doped films achieve a Tc value of ~42 K, with a high critical current (Jc > 1.4 kA cm−2 at 2 K) and upper critical fields (μ0Hc,∥(0) = 83.7 T, μ0Hc,⟂(0) = 110.3 T). Scanning transmission electron microscopy reveals that oxygen vacancies predominantly occupy planar NiO2 sites—unlike apical-site vacancies in bulk samples—due to compressive strain. Additionally, the elongated out-of-plane Ni–O bonds, exceeding those in pressurized bulk samples by 4%, likely weaken the interlayer \({d}_{{z}^{2}}\) d z 2 coupling and contribute to the reduced Tc in strained films.