Source capture
Authors Zhen Liang, Tianheng Wei, Wei Ren, Haoran Ji, Zheyuan Xie, Yanzhao Liu, Ziqiang Wang, Jian Wang
arXiv / Publisher https://arxiv.org/abs/2605.15703
PDF https://arxiv.org/pdf/2605.15703
Relevance score 5.834
Primary category cond-mat.supr-con
Published 2026-05-18
Research paradigm Experimental
Sample form Thin Film

Summary

Using ultra-low-temperature scanning tunneling microscopy/spectroscopy and electrical transport measurements, this study reports for the first time the observation of an energetically symmetric, flat-bottomed U-shaped superconducting gap with zero residual density of states and a gap magnitude exceeding 40 meV in (La,Pr)3Ni2O7 thin films. Transport measurements reveal an onset superconducting transition temperature above 40 K and a zero-resistance temperature above 20 K under ambient pressure. The tunneling spectra exhibit unconventional temperature evolution: as temperature increases, the U-shaped gap rapidly fills and transforms into a V-shaped gap; meanwhile, the gap decreases under a 14-tesla c-axis magnetic field. These temperature and magnetic field dependencies are consistent with superconducting gap behavior, indicating the existence of a nodeless gap function at ultralow temperatures. This discovery unveils the nature of high-temperature superconductivity in bilayer nickelates and provides important insights into achieving superconductivity above the boiling point of liquid nitrogen under ambient or zero pressure.

Materials

Methods

  • Ultra-low temperature scanning tunneling microscopy/spectroscopy
  • Electrical transport
  • Gigantic-oxidative atomic-layer-by-layer epitaxy

Keywords

  • u shaped gap
  • flat bottom gap
  • nodeless gap
  • coherence peaks
  • gap size >40 mev
  • unconventional temperature evolution
  • v shaped gap

Highlights

  • First observation of an extremely large U-shaped superconducting gap in bilayer nickelate thin films, suggesting potential for ambient-pressure superconductivity above 77 K.
  • Unconventional temperature evolution from U-shaped to V-shaped gap, not explainable by thermal broadening alone.

Conclusions

  • Observed an energy-symmetric, flat-bottom U-shaped gap with zero residual density of states and gap size ≈41.6 meV, consistent with a nodeless superconducting gap function.
  • The gap reduces under a 14 T magnetic field and exhibits unconventional temperature evolution: rapid filling from U-shaped to V-shaped with increasing temperature.
  • If the gap corresponds to the onset Tc, the ratio 2Δ/kBTc ≈20 indicates strong coupling; if compared to ARPES results, it suggests a potential local Tc above liquid nitrogen boiling point.

Main claims

  • An energy-symmetric, flat-bottom U-shaped gap with zero residual density of states and coherence peaks at ≈41.6 meV is observed in (La,Pr)3Ni2O7 thin films, indicating a nodeless superconducting gap.
    • Evidence: STS at 60 mK shows U-shaped gap with fully suppressed zero-bias conductance; gap size determined by peak separation
  • The gap is reduced by magnetic field (14 T) and exhibits unconventional temperature evolution: rapid filling from U-shaped to V-shaped as temperature increases from 60 mK to 45 K.
    • Evidence: Temperature-dependent STS show gap filling and shape change; thermal broadening alone cannot explain the transformation; magnetic field reduces gap
  • The observed large gap suggests potential for superconductivity above liquid nitrogen temperature at near-zero pressure.
    • Evidence: If2Δ/kBTc ≈ 9 as in ARPES, T_c would be ≈107 K; even with transport T_c ≈46 K, the strong-coupling ratio is unusually large

Workflow

  • thin_film_growth — High-quality films with ambient-pressure superconductivity.
    • Materials: (La,Pr)3Ni2O7; SrLaAlO4 substrate
    • Methods: gigantic-oxidative atomic-layer-by-layer epitaxy
    • Observations: superconducting thin films with onset T_c > 40K
  • transport_characterization — Robust superconductivity preserved throughout experiments.
    • Materials: same films before and after STM
    • Methods: four-probe resistivity measurement
    • Observations: zero resistance T_c > 20 K; onset T_c > 40K
  • stm_sts_measurements — Observation of nodeless superconducting gap with unconventional temperature evolution.
    • Materials: tip-treated local regions
    • Methods: STM imaging and STS spectroscopy; temperature and magnetic field dependence
    • Observations: energy-symmetric U-shaped gap with coherence peaks; gap size Δ ≈ 41.6 meV; rapid filling with temperature; reduction under field