Materials

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

Xinxin Wang, Yaqi Chen

Featured May 26, 2026

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Simply

Researchers found that carefully handling tiny nickelate samples in super-cold vacuum reveals their true, strong superconductivity with a unique U-shape, which is easily hidden by even slight oxygen loss.

In depth

The paper demonstrates that the true superconducting gap in bilayer nickelate films is a nodeless double gap (U-shaped spectra), but this intrinsic state is highly sensitive to oxygen content. They show that rapid, cryogenic sample transfer is crucial to preserve oxygen stoichiometry and observe this U-shaped gap, whereas longer exposure to vacuum leads to oxygen loss and a degraded V-shaped spectrum mixed with density-wave features.

Key Takeaways

1
Oxygen control is paramount for observing the intrinsic superconducting properties of bilayer nickelates, with sample transfer time directly correlating with oxygen loss.
2
The intrinsic superconducting state in oxygen-sufficient (La,Pr) $_{3}$ Ni $_{2}$ O $_{7}$ films exhibits a nodeless U-shaped double gap, characterized by two distinct energy scales (~14 meV and ~20 meV).
3
V-shaped tunnelling spectra, often observed in nickelates, are identified as a degraded superconducting state mixed with density-wave related spectral weight due to oxygen deficiency, rather than a signature of nodal superconductivity.

Conceptual Flow

HIGH LEVEL

Methodology: Preserving the True State

Researchers carefully moved tiny samples in a super-cold, empty space to keep them perfect, then used a special microscope to see their true electrical behavior.

Careful Sample Handling

See Tiny Details

Find True Superconductivity

Results: Intrinsic vs. Degraded Signals

They found that quick handling showed a clear, strong superconducting signal, but slow handling made the signal look weak and confusing, even if the material still seemed to work.

Quick Transfer

Slow Transfer

Compare Signals

Clear Superconductivity

Confused Signal