<p>The recent discovery of compressed superconductivity at 80 K in La<sub>3</sub>Ni<sub>2</sub>O<sub>7-δ</sub> has brought nickelates into the family of unconventional high-temperature superconductors. However, due to the challenges of directly probing the superconducting pairing mechanism under high-pressure, the pairing symmetry and gap structures of nickelate superconductors remain under intense debate. In this work, we successfully determine the microscopic information on the superconducting gap structure of La<sub>3</sub>Ni<sub>2</sub>O<sub>7-δ</sub> samples subjected to pressures exceeding 20 GPa, by constructing different conductance junctions within diamond anvil cells. By analyzing the temperature-dependent differential conductance spectra within the Blonder-Tinkham-Klapwijk (BTK) model, we have determined the superconducting energy gap at high pressure. The differential conductance curves reveal a two-gap structure with Δ<sub>s1</sub> = 23 meV and Δ<sub>s2</sub> = 6 meV, while the BTK fitting consistent with an <i>s</i>-like, two-gap spectrum. The gap ratio 2Δ<sub><i>s</i>1</sub>(0)/<i>k</i><sub><i>B</i></sub><i>T</i><sub><i>c</i></sub> is found to be 7.41, belonging to a family of strongly coupled superconductors. Our findings provide valuable insights into the superconducting gap structures of the pressure-induced superconducting nickelates.</p>

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Revealing superconducting gap in La3Ni2O7-δ by Andreev reflection spectroscopy under high pressure

  • Jianning Guo,
  • Yuzhi Chen,
  • Yulong Wang,
  • Hualei Sun,
  • Deyuan Hu,
  • Meng Wang,
  • Xiaoli Huang,
  • Tian Cui

摘要

The recent discovery of compressed superconductivity at 80 K in La3Ni2O7-δ has brought nickelates into the family of unconventional high-temperature superconductors. However, due to the challenges of directly probing the superconducting pairing mechanism under high-pressure, the pairing symmetry and gap structures of nickelate superconductors remain under intense debate. In this work, we successfully determine the microscopic information on the superconducting gap structure of La3Ni2O7-δ samples subjected to pressures exceeding 20 GPa, by constructing different conductance junctions within diamond anvil cells. By analyzing the temperature-dependent differential conductance spectra within the Blonder-Tinkham-Klapwijk (BTK) model, we have determined the superconducting energy gap at high pressure. The differential conductance curves reveal a two-gap structure with Δs1 = 23 meV and Δs2 = 6 meV, while the BTK fitting consistent with an s-like, two-gap spectrum. The gap ratio 2Δs1(0)/kBTc is found to be 7.41, belonging to a family of strongly coupled superconductors. Our findings provide valuable insights into the superconducting gap structures of the pressure-induced superconducting nickelates.