Pairing mechanism and superconductivity in pressurized La₅Ni₃O₁₁

Summary

Using density functional theory (DFT) and random phase approximation (RPA) calculations, this study systematically analyzes the electronic properties and superconducting mechanism of La₅Ni₃O₁₁ under high pressure. DFT band structures reveal that this material, characterized by alternating stacks of bilayer and monolayer NiO₂ planes, exhibits two nearly decoupled subbands originating from the bilayer and monolayer subsystems, respectively. RPA analysis indicates that superconducting pairing predominantly occurs within the bilayer subsystem, displaying an s±-wave pairing symmetry similar to that in pressurized La₃Ni₂O₇, while the monolayer subsystem primarily serves as a bridge connecting adjacent bilayers via extremely weak interlayer Josephson coupling (IJC) to achieve phase coherence along the c-axis. Under low pressure, increasing pressure significantly enhances IJC, thereby raising the bulk superconducting transition temperature (T_c); at sufficiently high pressures, the reduced density of states at the γ-pocket leads to a gradual decrease in T_c. This mechanism naturally explains the experimentally observed dome-shaped T_c-pressure dependence and reveals the distinct pressure response of mixed-phase compared to pure-phase nickelate superconductors.

Materials

• La₅Ni₃O₁₁

Methods

• DFT
• RPA
• tight-binding modeling
• Wannier downfolding

Keywords

• s± wave pairing
• interlayer josephson coupling
• pressure dome
• hybrid phase nickelate

Highlights

• Provides a natural understanding of the dome-shaped T_c pressure dependence in La₅Ni₃O₁₁.
• Shows that the alternating bilayer-single-layer structure leads to extremely weak interlayer Josephson coupling.
• Establishes a unified framework for hybrid phase nickelate superconductors.

Conclusions

• Superconducting pairing primarily occurs in the bilayer subsystem with s±-wave symmetry, similar to pressurized La₃Ni₂O₇.
• The single-layer subsystem serves as a bridge for inter-bilayer phase coherence via weak interlayer Josephson coupling.
• The dome-shaped pressure dependence of T_c arises from the interplay between enhanced IJC at low pressure and reduced DOS on the γ-pocket at high pressure.
• The hybrid phase exhibits distinct pressure response compared to pure bilayer nickelates.

Main claims

• Superconductivity in La₅Ni₃O₁₁ primarily occurs in the bilayer subsystem with s±-wave pairing symmetry
  • Evidence: From abstract: 'SC in this material occurs primarily within the bilayer subsystem exhibiting an s± wave pairing symmetry similar to that observed in pressurized La₃Ni₂O₇'
• Single-layer subsystem serves as a bridge facilitating inter-bilayer phase coherence via interlayer Josephson coupling, leading to dome-shaped T_c vs pressure
  • Evidence: From abstract: 'the single-layer subsystem mainly serves as a bridge facilitating the inter-bilayer phase coherence through the interlayer Josephson coupling (IJC)… dome-shaped pressure dependence of T_c observed experimentally is naturally understood'

Workflow

• density_functional_theory_calculations — Electronic structure consists of two nearly decoupled subsystems: bilayer and single-layer
  • Materials: La₅Ni₃O₁₁
  • Methods: DFT with PBE functional; VASP
  • Observations: band structure; Fermi surface
• tight_binding_model_construction — Constructed trilayer two-orbital tight-binding model
  • Materials: DFT band structure
  • Methods: Wannier downfolding
  • Observations: hopping integrals
• random_phase_approximation_analysis — s±-wave pairing dominates in bilayer subsystem; single-layer mediates interlayer Josephson coupling
  • Materials: Tight-binding model for bilayer subsystem
  • Methods: RPA for spin susceptibility and pairing
  • Observations: pairing eigenvalue; gap symmetry