Irrelevance of ¹H composition to superconductivity in infinite-layer nickelates from measurements of nuclear interactions

The discovery of superconductivity in infinite-layer nickelates extends our understanding of superconductivity. However, the significance of the incorporated 1H composition in enabling superconductivity in these materials has sparked considerable debate, primarily due to the challenges in quantifying ¹H with methods based on electron- or orbital-associated interactions. Herein, we demonstrate the irrelevance between superconductivity in infinite-layer nickelates and their incorporated ¹H composition by nuclear reaction analysis (NRA) and heavy-ion elastic recoil detection analysis (HIERDA). These approaches, which utilize nuclear interactions at the MeV energy scale, effectively eliminate conventional interferences, such as ionization, activation, and chemical bonds, allowing for accurate quantification of ¹H in superconducting La₀.₈Sr₀.₂NiO₂ (or Nd0.8Sr0.2NiO2). In particular, we observed a diverse range of ¹H compositions far beyond the previously expected critical dome, yet their critical temperature (TC) remained largely unchanged. Furthermore, superconductivity was shown to be achievable in La₀.₈Sr₀.₂NiO₂ reduced by Al without any hydrogen-related processes. Notably, the superconducting properties of the CaH₂-reduced La₀.₈Sr₀.₂NiO₂ remained stable after long-term exposure to air despite the high volatility of 1H in oxides. These findings indicate that the ¹H incorporation is neither critical nor relevant to the superconductivity of the infinite-layer nickelates.