Superconductivity and normal-state transport in compressively strained La₂PrNi₂O₇ thin films

Summary

The discovery of superconductivity under high pressure in Ruddlesden–Popper phases of bulk nickelates has sparked great interest in stabilizing ambient-pressure superconductivity in the thin-film form using epitaxial strain. Recently, signs of superconductivity have been observed in compressively strained bilayer nickelate thin films with an onset temperature exceeding 40 K, although with broad, two-step-like transitions. Here we report the intrinsic superconductivity and normal-state transport properties in compressively strained La₂PrNi₂O₇ thin films, achieved through a combination of isovalent Pr substitution, growth optimization and precision ozone annealing. The superconducting onset occurs above 48 K, with zero resistance reached above 30 K, and the critical current density at 1.4 K is 100-fold larger than previous reports. The normal-state resistivity exhibits quadratic temperature dependence indicative of Fermi liquid behaviour, and other phenomenological similarities to transport in overdoped cuprates suggest parallels in their emergent properties.

Materials

• La₂PrNi₂O₇

Methods

• Thin film growth
• Ozone annealing
• Transport measurements

Keywords

• fermi liquid behaviour
• overdoped cuprates parallels
• quadratic temperature dependence

Highlights

• Critical current density at 1.4 K is 100-fold larger than previous reports.
• Phenomenological similarities to transport in overdoped cuprates suggest parallels in emergent properties.

Conclusions

• Intrinsic superconductivity with onset above 48 K and zero resistance above 30 K is achieved.
• Normal-state resistivity exhibits quadratic temperature dependence indicative of Fermi liquid behaviour.

Main claims

• Intrinsic superconductivity achieved in compressively strained La₂PrNi₂O₇ thin films with onset above 48 K and zero resistance above 30 K.
  • Evidence: Abstract: 'superconducting onset occurs above 48 K, with zero resistance reached above 30 K',Text: 'Fig. 1a shows sharp transitions'
• Critical current density at 1.4 K is 100-fold larger than previous reports in bilayer nickelates.
  • Evidence: Abstract: 'critical current density at 1.4 K is 100-fold larger than previous reports'
• Normal-state resistivity exhibits quadratic temperature dependence indicative of Fermi liquid behaviour, similar to overdoped cuprates.
  • Evidence: Abstract: 'normal-state resistivity exhibits quadratic temperature dependence indicative of Fermi liquid behaviour',Text: 'parallel-resistor formula provides accurate fit'

Workflow

• growth_optimization — Optimal growth conditions identified for high-qualityLa₂PrNi₂O₇ films.
  • Materials: La₂PrNi₂O₇ target; SrLaAlO₄(001) substrates
  • Methods: pulsed laser deposition
  • Observations: systematic evolution of XRD peaks; optimal coherent growth at 150 mtorr
• ozone_annealing_optimization — Optimized single-step ozone annealing pathway enables bulk superconductivity.
  • Materials: as-grown films
  • Methods: ozone annealing with in situ transport feedback; variation of ozone concentration and temperature
  • Observations: phase boundary between bilayer and higher-order RP phases; superconducting films clustered at high T and high O₃
• structural_characterization — Films are coherently strained with tetragonal symmetry, occasional defects present.
  • Materials: optimized films
  • Methods: XRD θ-2θ scans; reciprocal space mapping; STEM
  • Observations: coherently strained films; occasional higher-order RP phases; one layer of (La,Pr)₂NiO₄ at interface
• transport_characterization — Intrinsic superconductivity with high Jc and sharp transitions demonstrated.
  • Materials: patterned films
  • Methods: resistivity vs T; Hall effect; critical current measurements; upper critical field extraction
  • Observations: sharp superconducting transitions; T_c onset >48 K, zero resistance >30K; Jc₁₀₀-fold higher than previous; diamagnetic response
• normal_state_analysis — Normal state exhibits Fermi liquid behavior, similar to overdoped cuprates.
  • Methods: parallel-resistor formula fitting; comparison to cuprate data
  • Observations: ρ(T) follows ρ0 + AT₂ with MIR limit; negative Hall coefficient comparable to overdoped cuprates