Correlation between superfluid density and transition temperature in infinite-layer nickelate superconductor Nd₁₋ₓSrₓNiO₂

Summary

This study employed scanning superconducting quantum interference microscopy to perform local magnetic susceptibility and magnetic flux imaging on infinite-layer nickelate superconductor Nd₀.₈Sr₀.₂NiO₂ thin films, aiming to elucidate the correlation between the zero-temperature superfluid density and the superconducting transition temperature. Owing to micron-scale inhomogeneities in the samples, spatial statistical analysis revealed that when the local (T_c) exceeds 8 K, (T_c) exhibits a linear relationship with (rhos0); conversely, when (T_c) is below 8 K, the dependence becomes sublinear (approximately (T_c propto rhos01/2)). This overall behavior closely resembles observations in overdoped cuprate superconductors, suggesting a potentially intimate intrinsic connection between the superconducting mechanisms of infinite-layer nickelate and cuprate superconductors.

Materials

• Nd₀.8Sr₀.2NiO₂

Methods

• Scanning superconducting quantum interference device (sSQUID) microscopy
• Susceptometry
• Magnetometry
• Mutual inductance

Keywords

• superfluid density
• phase stiffness
• thermal phase fluctuations
• quantum phase fluctuations
• uemura law

Highlights

• This work proposes a high-efficiency methodology of susceptometry imaging combined with spatial statistics to acquire continuous and dense T_c(ρs0) data from a single sample.
• The linear scaling for T_c>8 K suggests significant thermal phase fluctuations in Nd₀.8Sr₀.2NiO₂.

Conclusions

• Local T_c exhibits a linear relationship with ρs0 for T_c>8 K and a sublinear one (T_c ∝ ρs0^(1/2)) for T_c<8 K.
• The overall relationship is reminiscent of that reported in overdoped cuprate superconductors.
• This suggests a potentially intimate intrinsic connection between the superconducting mechanisms of infinite-layer nickelate and cuprate superconductors.

Main claims

• Local T_c and zero-temperature superfluid density in Nd₀.8Sr₀.2NiO₂ show a linear relationship for T_c > 8 K and sublinear (T_c ∝ ρs01/2) for T_c < 8 K.
  • Evidence: Abstract: 'spatial statistical analysis revealed that when the local T_c exceeds 8 K, T_c exhibits a linear relationship with ρs0; conversely, when T_c is below 8 K, the dependence becomes sublinear'
• This behavior is reminiscent of overdoped cuprate superconductors, suggesting a close intrinsic connection between the superconducting mechanisms.
  • Evidence: Abstract: 'This overall behavior closely resembles observations in overdoped cuprate superconductors, suggesting a potentially intimate intrinsic connection'

Workflow

• Sample growth and characterization
  • Materials: Nd₀.8Sr₀.2NiO₂ thin films on SrTiO₃ (001)
  • Methods: Pulsed laser deposition; Topotactic reduction
  • Observations: High-quality films with T_c up to 12.6K; Linear-in-temperature resistivity from 100-300K
• Scanning SQUID microscopy
  • Materials: Thin films
  • Methods: Local susceptometry and magnetometry; Variable temperature
  • Observations: Inhomogeneous superfluid density and T_c on micron scale; Weakly diamagnetic rings
• Data analysis and scaling — T_c-superfluid density relation in NSNO resembles overdoped cuprates
  • Materials: Susceptibility and T_c maps
  • Methods: Thin diamagnet film model; Spatial statistics; Extrapolation to zero temperature
  • Observations: T_c ∝ ρs0 for T_c > 8K; T_c ∝ √ρs0 for T_c < 8K