Source capture
Authors Wei Lv, Zihao Nie, Heng Wang, Haoliang Huang, Guangdi Zhou, Qikun Xue, Zhuoyu Chen
arXiv / Publisher https://arxiv.org/abs/2508.18107
PDF https://arxiv.org/pdf/2508.18107
Relevance score 5.561
Primary category cond-mat.supr-con
Published 2026-03-05
Research paradigm Experimental
Sample form Thin Film

Summary

This study successfully fabricated phase-pure, high-quality Ruddlesden-Popper nickelate Ln3Ni2O7 thin films on LaAlO3 and SrLaAlO4 substrates using the giant oxidation atomic layer epitaxy (GAE) method. Films grown under strongly oxidizing ozone atmosphere exhibited superconductivity without requiring post-annealing, with optimized Ln3Ni2O7/SrLaAlO4 films achieving an onset transition temperature (Tc,onset) as high as 50 K. Systematic investigation identified four key factors governing film crystallinity and superconducting performance: precise control of cation stoichiometry suppresses secondary phase formation; complete atomic layer-by-layer coverage combined with optimized interface reconstruction reduces stacking faults; accurate regulation of oxygen content is essential for achieving a single superconducting transition and high Tc,onset. The study also revealed that deviation in cation stoichiometry leads to the formation of Ni-rich or Ni-deficient secondary phases, inducing metal-insulator transitions or highly insulating behavior, respectively, while deviations in atomic layer coverage (e.g., 101.5%) still allow superconductivity but introduce residual resistance. Interface reconstruction, such as predisposing half-unit-cell Ln2NiO4 or annealing the SrLaAlO4 substrate, significantly improves film crystallinity. These findings provide important guidance for the layer-by-layer epitaxial growth of high-quality oxide high-temperature superconducting thin films.

Materials

Methods

Keywords

  • cation stoichiometry
  • atomic layer coverage
  • interface reconstruction
  • oxygen content
  • stacking faults
  • secondary phase
  • superconducting transition temperature

Highlights

  • Films grown under an ultrastrong oxidizing ozone atmosphere are superconducting without further post annealing.
  • The optimal Ln3Ni2O7/SrLaAlO4 superconducting film exhibits an onset transition temperature (Tc,onset) of 50 K.
  • Deviations in cation stoichiometry lead to the formation of Ni-rich or Ni-deficient secondary phases, inducing metal-insulator transitions or highly insulating behavior, respectively.
  • Interface reconstruction, such as predisposing half-unit-cell Ln2NiO4 or annealing the SrLaAlO4 substrate, significantly improves film crystallinity.

Conclusions

  • This study systematically investigates four critical factors governing the crystalline quality and superconducting properties of Ln3Ni2O7 thin films: cation stoichiometric precision, atomic layer coverage, interface reconstruction, and oxidation conditions.
  • Accurate cation stoichiometry suppresses the formation of secondary RP phases, enhancing crystalline phase purity.
  • Precise atomic layer coverage significantly mitigates stacking fault generation, thereby reducing XRD peak splitting and anomalous position shifts.
  • For SLAO substrates, thermal annealing or pre-deposition of a half-unit-cell 214-phase buffer layer enhances layer-by-layer growth at the interface, which can substantially improve overall crystalline structure and superconducting performance.
  • Under optimal ozone partial pressure, samples exhibit maximized Tc with single sharp superconducting transition.

Main claims

  • Precise cation stoichiometric control suppresses secondary phases (n=1 or n=3 RP phases) and is essential for superconductivity.
    • Evidence: full_text Fig. 2: Ni-rich (S1) shows 4310 phase; Ni-deficient (S3) shows 214 phase; only stoichiometric (S2) superconducts,abstract: 'precise cation stoichiometric control suppresses secondary phase formation'
  • Complete atomic layer coverage (100%) minimizes stacking faults; deviations (e.g., 101.5%) still allow superconductivity but with residual resistivity.
    • Evidence: full_text Fig. 4: S4 (116%) shows peak splitting; S5 (101.5%) shows asymmetric peaks; S6 (100%) symmetric,S5 still superconducting but with residual resistivity
  • Interface reconstruction (via annealed substrate or pre-deposited half-UC buffer) significantly improves crystallinity and superconducting performance.
    • Evidence: full_text Fig. 5: as-received substrate gives insulating film; annealed or buffered substrate gives superconducting film with complete XRD peaks,abstract: 'optimized interface reconstruction minimizes stacking faults'
  • Accurate oxygen content (optimal ozone partial pressure ≈1.2×10-2 mbar) is critical for single sharp superconducting transition and high Tc,onset.
    • Evidence: full_text Fig. 6: under-oxidized and over-oxidized show two-step transitions; optimally oxidized gives single transition at 50 K,abstract: 'accurate oxygen content regulation is essential'

Workflow

  • film_growth — GAE enables single-phase growth without post-annealing.
    • Materials: Ln3Ni2O7 (Ln = La, Pr, Sm); substrates: LaAlO3 (LAO), SrLaAlO4 (SLAO)
    • Methods: gigantic-oxidative atomic-layer-by-layer epitaxy (GAE); pulsed laser deposition of Ln2O3 and NiOx targets
    • Observations: RHEED oscillations indicate precise layer coverage
  • characterization — Four critical factors govern quality: stoichiometry, coverage, interface, oxygen content.
    • Materials: as-grown Ln3Ni2O7 films with varying stoichiometry, coverage, interface, oxidation
    • Methods: X-ray diffraction (XRD) θ-2θ scans; X-ray reflectivity (XRR); transport measurements
    • Observations: Optimal films show sharp XRD peaks and Tc,onset up to 50K