Superconducting Dome in La_3-xSrₓNi₂O_7-δ Thin Films

Summary

The ambient-pressure superconductivity in La₃⁢Ni₂⁢O₇ thin films via compressive epitaxial strain provides a highly accessible platform for diverse characterization techniques, facilitating the studies of high-temperature superconductivity. Here, we systematically map the phase diagram and reveal the superconducting dome with an electron-hole crossover in compressively strained La₃−𝑥⁢Sr𝑥⁢Ni₂⁢O₇−𝛿 thin films by simultaneously tuning Sr doping and oxygen content. The maximum transition temperature (𝑇𝑐) coincides with an anomalous sign change in the Hall coefficient (𝑅𝐻), reminiscent of electron-doped cuprates, which may signal a Fermi surface reconstruction. Beyond the superconducting dome, a ln⁡1/𝑇 insulating regime and a 𝑇-linear resistivity regime are also resolved, resembling behaviors observed in cuprates and infinite-layer nickelates. This work reveals a dome-shaped relationship between 𝑇𝑐 and 𝑅𝐻 and establishes a key framework for understanding unconventional superconductivity in nickelate systems.

Materials

• La_3-xSr_xNi₂O₇-δ

Methods

• Transport measurements
• Hall effect measurements

Keywords

• superconducting dome
• electron hole crossover
• fermi surface reconstruction
• t linear resistivity
• ln(1/t) insulating regime

Highlights

• The phase diagram resembles behaviors observed in cuprates and infinite-layer nickelates.
• Establishes a key framework for understanding unconventional superconductivity in nickelate systems.

Conclusions

• Maximum T_c coincides with an anomalous sign change in the Hall coefficient, signaling a Fermi surface reconstruction.
• A dome-shaped relationship between T_c and Hall coefficient is revealed.

Main claims

• A universal superconducting dome is revealed in the T_c vs RH phase space of compressively strained La₃−xSr_xNi₂O₇−δ thin films.
  • Evidence: Abstract: 'Here, we systematically map the phase diagram and reveal the superconducting dome with an electron-hole crossover…',Conclusion: 'a universal superconducting dome emerges'
• The maximum T_c coincides with an anomalous sign change in the Hall coefficient (RH), indicating an electron-hole crossover near optimal doping.
  • Evidence: Abstract: 'The maximum transition temperature (T_c) coincides with an anomalous sign change in the Hall coefficient (RH)',Text: 'the TH curve roughly extends to the peak of the superconducting dome'
• Beyond the superconducting dome, a ln(1/T) insulating regime and a T-linear resistivity regime are resolved, resembling behaviors in cuprates and infinite-layer nickelates.
  • Evidence: Abstract: 'Beyond the superconducting dome, a ln⁡1/T insulating regime and a T-linear resistivity regime are also resolved'

Workflow

• sample_growth_and_oxygen_tuning — Systematic control of Sr doping and oxygen content achieved.
  • Materials: SrTiO₃ capping layer; SrLaAlO₄ substrates; La, Sr, Ni sources
  • Methods: reactive molecular-beam epitaxy; ozone annealing; in situ vacuum annealing
  • Observations: as-grown films insulating; post-annealing metallic and superconducting
• structural_characterization — Film crystallinity remains high across all doping states.
  • Materials: thin films on substrates
  • Methods: XRD 2θ-ω scans; rocking curves; Scherrer analysis
  • Observations: high phase purity maintained; c-axis lattice constant varies within 0.5%
• transport_measurements — Superconducting dome with electron-hole crossover observed.
  • Materials: patterned Hall bars
  • Methods: resistivity vs temperature; Hall effect measurements
  • Observations: superconducting dome; T-linear resistivity above T_c; ln(1/T) insulating behavior; Hall coefficient sign change
• data_analysis_and_modeling — Fermi surface reconstruction likely near optimal doping, analogous to electron-doped cuprates.
  • Methods: two-band model; phase diagram construction
  • Observations: RH sign change tracks electron-hole crossover; T_c peaks at crossover