Atomically resolved intrinsic superconducting gap in (La,Pr)3Ni2O7 films

TL;DR

This study uses atomic-resolution scanning tunnelling microscopy to observe the intrinsic nodeless superconducting gap in (La,Pr)3Ni2O7 films, revealing details about pairing symmetry and surface effects.

Contribution

It provides the first atomic-scale measurement of the superconducting gap in bilayer nickelate ultrathin films, clarifying the pairing symmetry debate.

Findings

Reproducible U-shaped spectra with two gap scales of ~14 and ~20 meV.

Surface preservation techniques are crucial for accurate spectral measurements.

Oxygen loss can influence spectral features and superconductivity.

Abstract

Ruddlesden-Popper bilayer nickelates provide an emerging platform for studying high-temperature superconductivity, yet the superconducting pairing symmetry remains under debate. Here, we use atomic-resolution scanning tunnelling microscopy and spectroscopy to investigate superconducting 1.5-unit-cell (La,Pr)3Ni2O7 films grown on SrLaAlO4. A cryogenic ultrahigh-vacuum (UHV) sample transfer preserves an ordered sqrt(2) * sqrt(2) surface and yields reproducible U-shaped spectra with two gap scales of ~14 and ~20 meV and extended flat zero-conductance bottoms. By contrast, samples exposed for a longer time in UHV without cooling during transfer show V-shaped spectra despite retaining the surface reconstruction and a transport superconducting transition onset above 40 K. Wide-energy-range spectra indicate that oxygen loss can mix density-wave-related spectral weight. Our measurements provide an atomic-scale observation of the intrinsic nodeless superconducting gap in bilayer nickelate ultrathin films.