Superconductivity onset above 60 K in ambient-pressure nickelate films

Summary

This study employed the enormous oxidation atomic layer epitaxy method to grow (La,Pr)₃Ni₂O₇ thin films on SrLaAlO₄ substrates under extreme non-equilibrium conditions, achieving a superconducting onset transition temperature of approximately 63 K at ambient pressure, with zero-resistance temperature reaching about 37 K and diamagnetic signal onset at around 23 K. This method overcomes the structural instability of the metastable superconducting phase through high-temperature and in-situ sufficient oxidation; X-ray diffraction and scanning transmission electron microscopy confirmed that the films possess large-scale crystalline purity. Transport measurements reveal a systematic evolution of the normal-state resistivity temperature power-law exponent α from Fermi liquid behavior (α≈2) in samples with low onset transition temperatures to strange metal behavior (α≈1) in samples with high onset transition temperatures, directly correlating enhanced superconductivity with non-Fermi liquid behavior. The vortex melting phase diagram constructed via mutual inductance technique indicates that the two-dimensional melting limit is suppressed to near zero, with interlayer coupling strength significantly stronger than that of bismuth-based cuprates. These results demonstrate that nickelates are strange metal high-temperature superconductors with strong interlayer coupling at ambient pressure.

Materials

• (La,Pr)₃Ni₂O₇

Methods

• gigantic-oxidative atomic-layer-by-layer epitaxy (GAE)
• X-ray diffraction (XRD)
• synchrotron XRD
• reciprocal space mapping
• STEM
• energy-dispersive X-ray spectroscopy (EDS)
• transport measurements (R-T)
• mutual inductance technique
• power-law fitting for resistivity exponent

Keywords

• strange metal behavior
• linear in t resistivity
• vortex melting
• interlayer coupling
• non equilibrium growth
• coherent interface
• oxygen stoichiometry
• berezinskii kosterlitz thouless (bkt) transition

Highlights

• The GAE method creates an extreme non-equilibrium growth regime that decouples the conflict between crystallinity and oxygenation.
• Mapping the vortex melting phase diagram reveals the 2D melting limit suppressed to near zero, demonstrating significantly stronger interlayer coupling than that of cuprates.
• The nickelates are identified as an ambient-pressure strange-metal high-temperature superconductor with strong interlayer coupling.

Conclusions

• We report ambient-pressure superconductivity onset at ≈63 K in epitaxial (La,Pr)₃Ni₂O₇ thin films.
• Transport measurements reveal a zero-resistance temperature reaching ≈37 K, while mutual inductance measurements demonstrate a robust diamagnetic transition starting at ≈23 K.
• These films exhibit a systematic evolution in their normal-state resistivity-temperature curve: the power-law exponent α evolves from Fermi-liquid-like (α≈2) at lower T_c,onset to strange-metal-like (α≈1) in higher T_c,onset samples.

Main claims

• Ambient-pressure superconductivity onset at ≈63 K and zero-resistance at ≈37 K is achieved in (La,Pr)₃Ni₂O₇ films via extreme non-equilibrium GAE method.
  • Evidence: abstract: 'ambient-pressure superconductivity onset at ≈63 K' and 'zero-resistance temperature reaching ≈37 K',full_text Fig. 1c: S₁ film shows Tc_onset = 63 K, Tc_zero ≈ 30 K (S₁) and 37 K (S₂)
• The normal-state resistivity exponent α evolves from Fermi-liquid-like (α≈2) at lower Tc_onset to strange-metal-like (α≈1) at higher Tc_onset, directly linking enhanced superconductivity to non-Fermi liquid behavior.
  • Evidence: abstract: 'the power-law exponent α evolves from Fermi-liquid-like (α ≈2) at lower Tc_onset to strange-metal-like (α ≈1) in higher Tc_onset samples',full_text Fig. 1d,e: clear correlation shown for 90 samples with various La:Pr ratios
• Mutual inductance measurements reveal a robust diamagnetic transition at ≈23 K and a vortex melting phase diagram with 2D melting limit suppressed to near zero, indicating much stronger interlayer coupling than cuprates (e.g., Bi-2212).
  • Evidence: abstract: 'Mapping the vortex melting phase diagram… reveals 2D melting limit suppressed to near zero, which demonstrates significantly stronger interlayer coupling than that of cuprates',full_text Fig. 2: TM onset at 23 K, Bcr≈200 T from fitting, compared to Bi-2212 Bcr ≈2T
• The enhanced performance is enabled by pushing GAE into an extreme non-equilibrium regime that simultaneously improves crystallinity and achieves full oxygenation.
  • Evidence: abstract: 'This T_c leap is enabled by pushing our GAE method into an extreme non-equilibrium growth regime',full_text: 'GAE accesses a unique high-temperature and high-oxidation regime' and STEM/XRD confirm large-scale crystalline purity

Workflow

• film_growth — Extreme non-equilibrium GAE enables single-step synthesis with Tc_onset >60 K.
  • Materials: (La,Pr)₃Ni₂O₇ thin films on SrLaAlO₄ (001) substrates
  • Methods: gigantic-oxidative atomic-layer-by-layer epitaxy (GAE); alternating ablation of (La,Pr)O_x and NiO_x targets
  • Observations: RHEED oscillations show layer-by-layer growth; Films are superconducting as-grown without post-annealing
• transport_and_mutual_inductance_measurements — Enhanced superconductivity correlates with strange-metal normal state and strong interlayer coupling.
  • Materials: (La,Pr)₃Ni₂O₇ films with various oxygen stoichiometries
  • Methods: four-terminal AC lock-in transport; two-coil mutual inductance technique; XRD and STEM
  • Observations: Tc_onset up to 63 K, Tc_zero up to 37K; Normal-state exponent α evolves from ≈2 to ≈1 with increasing Tc_onset; Vortex melting temperature TM ≈23 K at zero field, strong interlayer coupling