Revealing superconducting gap in La<sub>3</sub>Ni<sub>2</sub>O<sub>7-δ</sub> by Andreev reflection spectroscopy under high pressure.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 41330915.
- Also identified by DOI 10.1038/s41467-025-65865-y and PMC identifier 12672831.
- Licence recorded as CC BY-NC-ND.
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Abstract
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 s-like, two-gap spectrum. The gap ratio 2Δ<sub>s1</sub>(0)/k<sub>B</sub>T<sub>c</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.