Source capture
Authors Shu Kamiyama, Reo Kohno, Yuto Hoshi, Kensei Ushio, Daiki Nakaoka, Hirofumi Sakakibara, Kazuhiko Kuroki
arXiv / Publisher https://arxiv.org/abs/2603.11771
PDF https://arxiv.org/pdf/2603.11771
Relevance score 5.541
Primary category cond-mat.supr-con
Published 2026-03-13
Research paradigm Theoretical
Sample form Unknown

Summary

This study establishes a correspondence between the multi-orbital Hubbard model and the bilayer Hubbard model, proposing an orbital-space bilayer model (OSBM) in which the orbital energy level difference ΔE plays a role analogous to interlayer hopping in a real-space bilayer model, and superconductivity is enhanced in the incipient-band regime. Based on this, the theory predicts that the reduced bilayer nickelate La3Ni2O6, under appropriate hole doping, can serve as a candidate OSBM superconductor. A tight-binding model constructed from first principles reveals a large ΔE between the Ni dx2-y2 orbital and other d orbitals due to the absence of apical oxygen atoms. Using the fluctuation-exchange approximation, calculations show that in the incipient-band scenario, intersite interactions can drive s±-wave superconductivity, where the superconducting gap function changes sign between the dx2-y2 band and other d-orbital bands. The study also examines the energetic and dynamic stability of the crystal structure under atomic substitution and pressure. Although La3Ni2O7 and La3Ni2O6 share similar chemical formulas, this work suggests that the latter may realize a completely different pairing mechanism.

Materials

Methods

Keywords

Highlights

  • The study establishes a correspondence between the multi-orbital Hubbard model and the bilayer Hubbard model, proposing an orbital-space bilayer model (OSBM).
  • Large ΔE between Ni dx2-y2 and other d orbitals is obtained due to the absence of outer apical oxygens.
  • The energy difference between T and T′ structures varies under external hydrostatic pressure or internal pressure effects arising from differences in ionic radii.

Conclusions

  • s±-wave superconductivity can be enhanced by hole doping due to interorbital interactions in both T and T′ structures.
  • This enhancement originates from the OSBM mechanism, where the Fermi level approaches the lower bands and the incipient-band situation is realized.
  • Superconductivity is not significantly enhanced by interorbital interaction between dx2-y2 and d3z2-r2 alone; rather, it is enhanced by interorbital interactions involving all four orbitals in the lower bands.

Main claims

  • Hole-doped La3Ni2O6 exhibits s±-wave superconductivity driven by interorbital interactions in the incipient-band regime.
    • Evidence: Abstract,Full text: FLEX calculations indicate emergence of s±-wave superconductivity driven by interorbital interactions in an incipient-band situation.
  • The large orbital level offset ΔE between dx2-y2 and other d orbitals due to absence of apical oxygen is crucial for OSBM superconductivity.
    • Evidence: Abstract,Full text: A large ΔE between the Ni dx2-y2 and the other d orbitals is obtained due to the absence of outer apical oxygens.
  • Hole doping can induce a structural transition from T' to T structure even at ambient pressure.
    • Evidence: Full text,Section III E: Enthalpy difference calculations show T structure becomes more stable upon Sr/Ba doping.

Workflow

  • band_structure_calculation
    • Materials: La3Ni2O6
    • Methods: DFT (PBEsol); GGA+U; QSGW
    • Observations: large orbital level offset ΔE between dx2-y2 and other d orbitals
  • model_construction
    • Methods: tight-binding model from Wannier functions; cRPA for interaction parameters
  • superconductivity_analysis
    • Methods: FLEX approximation; linearized Eliashberg equation
    • Observations: s±-wave superconductivity driven by interorbital interactions in incipient-band regime
  • structural_stability_analysis
    • Methods: phonon dispersion calculations; enthalpy comparison
    • Observations: T and T' structures can be stabilized by doping and pressure