Enhanced and robust superconductivity in La₀.8Sr₀.2NiO₂ membranes compressed up to 210 GPa

Summary

Researchers have prepared freestanding La₀.₈Sr₀.₂NiO₂ thin films and performed electrical resistance measurements using a diamond anvil cell at ultrahigh pressures up to 210 GPa. The experiments reveal a dome-shaped evolution of the superconducting onset transition temperature: beginning at approximately 16 K at ambient pressure, it rises monotonically with increasing pressure, reaches a peak of 74.5 K at 146 GPa, and then slowly decreases while still retaining 57.4 K at 210 GPa. Through derivative analysis and magnetic field suppression experiments, it is confirmed that this enhancement in transition temperature stems from an intrinsic strengthening of superconductivity, rather than a simple broadening of the transition width. A comparison with Nd₀.₈₅Sr₀.₁₅NiO₂ films shows that both exhibit a linear increase with pressure below 60 GPa with similar slopes, though their behaviors diverge at higher pressures; nonetheless, the maximum onset temperature for both is approximately 75 K, indicating that the NiO₂ planes dominate the superconductivity and that the magnetic moments of rare-earth f orbitals have minimal influence. This work represents the first observation of robust superconductivity in oxide superconductors over such a wide pressure range, demonstrating that the pairing strength in infinite-layer nickelates remains unsuppressed under extreme compression, and provides important clues for understanding the mechanism of unconventional superconductivity.

Materials

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Methods

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Keywords

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Highlights

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Conclusions

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Main claims

• Superconductivity in freestanding La₀.8Sr₀.2NiO₂ membranes is robust up to 210 GPa with a dome-like T_c onset, peaking at 74.5 K at 146 GPa.
  • Evidence: Fig. 2c–f: R(T) at various pressures show persistent resistive drops; T_c[onset] values extracted and plotted in Fig. 5.
• The enhancement is intrinsic, not due to transition broadening, as evidenced by derivative analysis and magnetic field suppression.
  • Evidence: Fig. 3: dR/dT analysis shows T_c[m] increases significantly; Fig. 4: Hc₂ enhanced at 80 GPa.
• Comparison with Nd₀.85Sr₀.15NiO₂ shows both peak near 75 K, indicating NiO₂ planes govern superconductivity with little influence from rare-earth f-orbitals.
  • Evidence: Fig. 5 includes Nd data; both maxima ≈75 K at different pressures; text states f-orbital moment has little impact.
• This robustness is unprecedented among high-T_c oxide superconductors, with most systems suppressed at much lower pressures.
  • Evidence: Fig. 5 comparative data: cuprates, bismuthates suppressed below 40 GPa; text mentions only infinite-layer nickelates persist above 200 GPa.

Workflow

• freestanding_membrane_preparation — Freestanding single-crystal La₀.8Sr₀.2NiO₂ membranes are successfully synthesized.
  • Materials: La₀.8Sr₀.2NiO₃ perovskite thin film; SrTiO₃ substrate; Sr₄Al₂O₇ sacrificial layer; CaH₂ reductant
  • Methods: molecular-beam epitaxy; topotactic reduction; chemical release in deionized water
  • Observations: highly oriented (00l) XRD peaks; superconducting transition at ≈16 K before transfer
• high_pressure_device_assembly — Membranes are integrated into DAC devices for high-pressure resistance measurements.
  • Materials: freestanding membrane; diamond anvil cell; gold electrodes
  • Methods: micromanipulator transfer onto diamond culet; electrode deposition
  • Observations: optical image of membrane with four electrodes
• high_pressure_resistance_measurements — Superconducting transition persists up to 210 GPa, with T_c[onset] exhibiting a dome-like pressure dependence.
  • Materials: La₀.8Sr₀.2NiO₂ membrane devices
  • Methods: resistivity measurement under pressure; magnetic field application up to 7T
  • Observations: resistance drops at T_c[onset] values; T_c[onset] increases with pressure up to 146 GPa then decreases
• data_analysis — The increase in T_c[onset] reflects genuine strengthening of superconductivity, not just broadening.
  • Materials: R(T) data; dR/dT curves; magnetic field sweeps
  • Methods: two-line intersection method for T_c[onset]; derivative analysis for T_c[m]; upper critical field determination
  • Observations: T_c[m] increases fourfold; transition width increases but cannot account for T_c[onset] shift; Hc₂ enhanced under pressure
• interpretation — Infinite-layer nickelates exhibit uniquely robust superconductivity under extreme compression, dominated by NiO₂ planes.
  • Materials: phase diagram data from multiple samples and literature
  • Methods: construction of P-T phase diagram; comparison with Nd₀.85Sr₀.15NiO₂ and other superconductors
  • Observations: dome-like behavior with maximum 74.5 K at 146 GPa; both La and Nd nickelates peak at ≈75K; other oxides show suppression at much lower pressures