Materials

Thermodynamic phase transition, pairing symmetry and Fermi surface topology in Ruddlesden-Popper nickelate films

Yu Miao, Zhiwei Wang, et al.

Featured August 9, 2026

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Simply

Scientists found that a new nickelate material becomes a superconductor with a clear energy jump, proving its special state and showing it pairs electrons in a simple, nodeless way, unlike some other complex superconductors.

In depth

The paper provides the first direct thermodynamic evidence for a superconducting phase transition in Ruddlesden-Popper nickelates by observing a clear electronic specific heat jump at the critical temperature. They also unambiguously identify a nodeless superconducting order parameter in the absence of a pseudogap, strongly supporting s-wave pairing symmetry. Furthermore, the study clarifies the complex relationship between Fermi surface topology, epitaxial strain, and the emergence of superconductivity.

Key Takeaways

1
The study establishes the missing thermodynamic evidence for superconducting phase transition in nickelates by observing an electronic specific heat jump at $T_{C}$ and the emergence of a nonzero superconducting order parameter.
2
A pure nodeless superconducting order parameter is identified in the absence of a pseudogap, providing direct evidence for s-wave (s $\pm$ ) pairing symmetry, inconsistent with d-wave.
3
Strain-dependent measurements reveal that while the $γ$ Fermi pocket is always present, its existence does not guarantee superconductivity, suggesting other factors like electron-boson coupling or structural modifications are crucial.

Conceptual Flow

HIGH LEVEL

Methodology: Probing Electron Behavior

Scientists used a special light to see how electrons move in the material, then used math to figure out its heat behavior.

Nickelate Material

Shine Special Light

Electron Energy Data

Electron Heat Capacity

Results: Clear Superconducting Proof

They found a clear energy gap and a heat jump, showing the material is a true superconductor with a simple electron pairing.

Electron Energy Data

Electron Heat Capacity

Analyze Patterns

Clear Superconducting Gap

Heat Jump at Transition