Nodeless superconducting gap and electron-boson coupling in (La,Pr,Sm)${}_3$Ni${}_2$O${}_7$ films

Abstract

The discovery of superconductivity in Ruddlesden-Popper (RP) bilayer nickelate films under ambient pressure provides an unprecedented opportunity to directly investigate electronic energy scales of the superconducting state and the pairing mechanism. Here, we report angle-resolved photoemission spectroscopy measurements of superconducting (La,Pr,Sm)${}_3$Ni${}_2$O${}_7$ thin films epitaxially grown on SrLaAlO${}_4$ substrates by developing an ultra-high vacuum low-temperature quenching and transfer technique. A finite superconducting gap of ~18 meV with pronounced coherence peak is observed along the Brillouin zone diagonal direction. Remarkably, the finite superconducting gap persists across the entire Brillouin zone of the underlying Fermi surfaces, revealing the absence of gap nodes. An abrupt band renormalization, manifested as a kink in the energy-momentum dispersion at ~70 meV below the Fermi level, indicates an electron-boson coupling in the system. The simultaneous observation of a nodeless superconducting gap and electron-boson coupling provides crucial insights into the pairing symmetry and gluing mechanism in high-T${}_c$ RP bilayer nickelates.

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Cited by in corpus (1)

• Reducing the strain required for ambient-pressure superconductivity in bilayer nickelates