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This study employs first-principles density functional theory (GGA and GGA+U) to investigate the electronic and magnetic properties of La3Ni2O5F, which features a bilayer NiO2 infinite-layer structure where La(O/F)La blocking layers achieve strict isolation of the NiO2 bilayers, forming a purely two-dimensional electronic and magnetic system. Calculations reveal an E* single band composed of electron density in the interstitial region, which is not associated with any atomic orbital, dips below the Fermi level along the M-A direction, and provides a self-doping of 0.09 holes per Ni, resulting in an actual Ni valence of +1.09; the Fermi surface of this E* band is cylindrical, occupying 9% of the Brillouin zone area. The dpσ band is nearly half-filled but is shifted near a Van Hove singularity due to the self-doping, and the magnetic response exhibits anomalous characteristics distinct from previous nickelates, with the magnetic susceptibility tending to vanish under a large magnetic field. The absence of a magnetic phase transition can be attributed to strong two-dimensional spin fluctuations and the self-doping effect away from half-filling, revealing the unique behavior of Ni¹⁺ ions in this system and the critical influence of the interfacial blocking layer on the interstitial band morphology.

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This study employs atomic-resolution scanning tunneling microscopy and spectroscopy to characterize 1.5 unit-cell-thick (La,Pr)₃Ni₂O₇ ultrathin films grown on SrLaAlO₄. Through low-temperature ultrahigh vacuum sample transfer, an ordered √2×√2 surface reconstruction is preserved, and a U-shaped spectrum with two gap scales (approximately 14 and 20 meV) and a flat zero-bias conductance is observed in the tunneling spectra, indicating a nodeless superconducting gap. In contrast, if the sample is exposed to ultrahigh vacuum for a longer time during transfer without cooling, although the surface reconstruction and a transport superconducting onset temperature above 40 K are maintained, the tunneling spectrum becomes V-shaped, and the wide-energy spectrum shows that oxygen deficiency mixes spectral weight related to density waves. By comparing samples with different transfer times, it is determined that controlling the oxygen content is necessary to obtain an intrinsic superconducting gap, providing atomic-scale observational evidence for the intrinsic nodeless superconducting gap in bilayer nickelate ultrathin films.

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