Source capture
Authors Yichen Hua, Wenxin He, Wei-Qiang Chen, Jian-jian Miao, Changming Yue
arXiv / Publisher https://arxiv.org/abs/2603.02685
PDF https://arxiv.org/pdf/2603.02685
Relevance score 5.512
Primary category cond-mat.supr-con
Published 2026-03-09
Research paradigm Theoretical
Sample form Thin Film

Summary

This study systematically analyzes a two-site, two-orbital model of the La3Ni2O7 thin-film superconductor under ambient pressure within a weakly correlated system, employing the fluctuation exchange (FLEX) approximation, with a focus on the influence of hole doping on superconducting properties. Through a detailed examination of the Fermi surface topology, it is found that when the δ pocket, formed by the dz2 antibonding orbital, emerges near the Γ point, the nesting between the δ and γ pockets, together with the nesting between the α and β pockets, collectively enhances s±-wave pairing at the corresponding wave vectors. The study further proposes that this enhancement mechanism of spin-fluctuation-induced pairing, driven by Fermi surface nesting, may provide a feasible route to raising the superconducting transition temperature. This work offers theoretical guidance for understanding the pairing mechanism of nickel-based thin-film superconductors under ambient pressure and for exploring higher-performance superconducting materials.

Materials

Methods

  • FLEX (fluctuation exchange) approximation
  • linearized Eliashberg equation
  • density functional theory (DFT)-based tight-binding modeling
  • spin susceptibility analysis

Keywords

Highlights

  • When a δ pocket composed of the dz2 antibonding orbital emerges near the Γ point, its nesting with the γ pocket, together with the nesting between the α and β pockets, leads to a mutual enhancement of s±-wave pairing.
  • If the δ pocket could be restored to the Fermi surface in new material realizations through strain or doping, it could lead to higher superconducting transition temperature.

Conclusions

  • We used the FLEX method to study a previously proposed model Hamiltonian for the ambient pressure La3Ni2O7 film superconductor.
  • We conclude that the complex spin fluctuations induced by repulsive Coulomb interactions can facilitate s±-wave pairing on the orbitals.
  • We found that a non-trivial δ pocket in the studied band structure significantly enhances the tendency toward s±-wave superconductivity.
  • By artificially tuning the presence or absence of the δ pocket, we confirmed this superconductivity enhancing mechanism.

Main claims

  • Fermi surface nesting between the δ pocket (d_z2 antibonding orbital) and the γ pocket, together with α-β nesting, mutually enhances s±-wave pairing.
    • Evidence: abstract: 'nesting between the δ and γ pockets, together with the nesting between the α and β pockets, leads to a mutual enhancement of s±-wave pairing',full_text: 'spin susceptibility at optimal doping is dominated by peaks at q1 and q2'
  • The δ pocket significantly contributes to superconductivity; artificially removing it reduces the pairing eigenvalue λ.
    • Evidence: full_text Fig. 4(c,f): λ is consistently higher when δ pocket is present,full_text: 'the enhancement mechanism of spin-fluctuation-induced pairing driven by Fermi surface nesting'
  • This nesting-driven enhancement mechanism may provide a viable route to raising Tc in nickelate thin films.
    • Evidence: abstract: 'this nesting-driven enhancement of spin-fluctuation-induced pairing may provide a viable mechanism for enhancing superconductivity',full_text: 'presence of the δ pocket and its enhancement mechanism could lead to a higher Tc'

Workflow

  • model_construction — The minimal model captures essential physics of ambient-pressure films.
    • Materials: two-site two-orbital Hubbard model for La3Ni2O7 thin film
    • Methods: tight-binding parametrization from DFT; Hubbard-Kanamori interaction
    • Observations: Band structure agrees with DFT
  • FLEX_calculations — FLEX captures renormalized Fermi surface and spin fluctuations.
    • Materials: self-consistent Green's functions and susceptibilities
    • Methods: fluctuation exchange (FLEX) approximation; 48×48×48 k-grid; T = 0.01 eV
    • Observations: Fermi surface with α, β, γ, δ pockets; spin susceptibility peaks at nesting vectors
  • Eliashberg_analysis — Fermi surface nesting between δ and γ pockets enhances s±-wave pairing.
    • Materials: converged FLEX quantities
    • Methods: linearized Eliashberg equation; power method for largest eigenvalue λ
    • Observations: s±-wave eigenvalue enhanced near optimal doping; d-wave competitive in overdoped region