Superconducting gap structure and bosonic mode in La2PrNi2O7 thin films at ambient pressure

Abstract

The recent discovery of high temperature superconductivity in nickelate systems has generated tremendous interests in the field of superconductivity. The core issue to understand the superconductivity mechanism is about the superconducting gap and its symmetry. By using the substrate of SrLaAlO4(00l), we have successfully synthesized the superconducting thin film of La2PrNi2O7 with Tc(onset) = 41.5 K. Superconducting tunneling spectra are successfully measured on the terraces after we expose the superconducting layer by using the tip-excavation technique. The spectrum shows a two-gap structure with Delta1=19 meV, Delta2=6-8 meV, and fittings based on the Dynes model indicate that the dominant gap should have an anisotropic s-wave structure, this allows us to put the priority in selecting the s+- among the two arguable pairing models: s+- and d-wave. Furthermore, a clear bosonic mode with energy Omega=30+-2 meV is observed, which further supports a sign reversal gap. Our results shed new light in understanding the mystery of superconductivity in bilayer nickelate superconductors.