First-Principles Evidence for Strongly Correlated Superconductivity Driven by Structural Variations in La₃Ni₂O₇

Summary

This study systematically analyzes the electronic correlation behavior of La₃Ni₂O₇ within the superconducting pressure range using first-principles simulations combined with constrained random phase approximation and ab initio molecular dynamics. The results show that, accompanying the structural phase transition, the effective on-site repulsion of Ni e_g orbitals is significantly enhanced, attributed to the dynamic balance between orbital localization and competing screening channels, particularly the spacer-layer La bands. This enhancement region aligns remarkably well with the experimentally observed right-triangular superconducting dome, reaching a peak correlation strength at 18 GPa that corresponds to the highest superconducting critical temperature. Finite-temperature simulations further clarify the boundaries of the structural phase diagram, while calculations on Ac₃Ni₂O₇ confirm the critical role of A-site cations in the pressure-driven evolution of electronic correlations. These findings directly reveal how structural changes drive unconventional superconductivity by modulating the strength of electronic correlations.

Materials

• La₃Ni₂O₇
• Ac₃Ni₂O₇

Methods

• DFT
• cRPA
• AIMD
• Wannier downfolding

Keywords

• electronic correlations
• structural phase transition
• screening
• a site cation substitution

Highlights

• First ab initio evidence linking enhanced correlations to the right-triangular superconducting dome in La₃Ni₂O₇.
• Uses cRPA to show that screening from La spacer bands dominates in the high-pressure limit, reducing correlations.
• Predicts that Ac₃Ni₂O₇ may exhibit superconductivity near ambient pressure but with lower maximal T_c.

Conclusions

• The effective on-site repulsion in the Ni eg bands is significantly enhanced within the superconducting pressure range, peaking at 18 GPa.
• This enhancement arises from a competition between orbital localization and competing screening from La spacer bands.
• The superconducting region in the P-T phase diagram coincides with the region of enhanced correlations, closely tracking the critical temperature.
• Ac₃Ni₂O₇ confirms the crucial role of the A-site cation in shaping pressure-driven evolution of correlations.
• Finite-temperature AIMD simulations clarify the structural phase diagram and origin of the right-triangular dome.

Main claims

• Enhanced electronic correlations coincide with the right-triangular superconducting region in La₃Ni₂O₇ phase diagram
  • Evidence: From abstract: 'superconducting region in the La₃Ni₂O₇ phase diagram coincides with a region of enhanced electronic correlations, which show a close correspondence with the critical temperature'
• At low pressures, enhanced correlations due to structural transition; at high pressures, screening from La 5d bands reduces correlations
  • Evidence: From text: 'pressure-driven competition between orbital localisation, reduced octahedral distortions, and band splitting… and increased screening from the spacer La bands',From abstract: 'We attribute this increase to an interplay between orbital localisation and competing screening channels'

Workflow

• density_functional_theory_calculations — Structural phase transition from orthorhombic to tetragonal at ≈10 GPa
  • Materials: La₃Ni₂O₇; Ac₃Ni₂O₇
  • Methods: DFT with PBE functional; structural optimization at fixed pressures
  • Observations: lattice parameters; bond angles
• constrained_random_phase_approximation — Effective on-site repulsion increases with pressure due to orbital localization and reduced screening
  • Materials: Optimized structures
  • Methods: cRPA for effective interactions; Wannier downfolding
  • Observations: screened Coulomb interactions U, U', J
• ab_initio_molecular_dynamics_simulations — Finite-temperature phase boundaries determined; right-triangular superconducting dome correlates with enhanced correlations
  • Materials: La₃Ni₂O₇
  • Methods: AIMD in NPT ensemble
  • Observations: time-averaged lattice constants; bond angles