[Paper Review] Theoretical proposal of superconductivity in hole-doped reduced bilayer nickelate La3Ni2O6: a manifestation of orbital-space bilayer model with incipient bands

Shu Kamiyama, Reo Kohno+5 more|arXiv (Cornell University)|Mar 12, 2026

Magnetic and transport properties of perovskites and related materials0 citations

TL;DR

The paper proposes that hole-doped La3Ni2O6 can realize an orbital-space bilayer model (OSBM) superconductivity, showing s±-wave pairing driven by interorbital interactions in an incipient-band regime using first-principles-derived five-orbital models and FLEX analysis.

ABSTRACT

A correspondence exists between the multi-orbital Hubbard model and the bilayer Hubbard model, in which superconductivity is optimized in an incipient-band regime in both cases. In the multi-orbital system, the orbital level offset $ΔE$ plays a role analogous to the interlayer hopping in bilayer systems, and superconductivity is enhanced for large $ΔE$. We refer to such a multi-orbital model as an orbital-space bilayer model (OSBM). In this study, we theoretically propose that a reduced bilayer nickelate La$_3$Ni$_2$O$_6$ can be a candidate for a superconductor described by OSBM when an appropriate amount of holes is doped. By constructing a tight-binding model based on first-principles calculations, a large $ΔE$ between the Ni $d_{x^2-y^2}$ and the other $d$ orbitals is obtained due to the absence of outer apical oxygens. Furthermore, our fluctuation exchange approximation calculations indicate the emergence of $s\pm$-wave superconductivity driven by interorbital interactions in an incipient-band situation, where the superconducting gap function changes its sign between the $d_{x^2-y^2}$ and other $d$ orbital bands. We also investigate the energetic and dynamical stability of the crystal structure under atomic substitution and pressure. Although La$_3$Ni$_2$O$_7$ and La$_3$Ni$_2$O$_6$ share a similar chemical formula, our study shows that an entirely different pairing mechanism can take place in the latter.

Motivation & Objective

• Motivate OSBM as a framework linking multi-orbital and bilayer Hubbard models for high-Tc superconductivity.
• Demonstrate that La3Ni2O6 under hole doping can realize an incipient-band OSBM regime.
• Construct realistic tight-binding models from first-principles and assess superconductivity with FLEX and Eliashberg analysis.
• Evaluate how interorbital interactions and ∆E (orbital level offsets) influence pairing.
• Assess structural stability under pressure and chemical substitution as it relates to OSBM viability.

Proposed method

• Construct five-orbital Ni-d tight-binding models from first-principles band structures (GGA, GGA+U with U=3 eV, and QSGW) for T and T′ structures.
• Derive Wannier functions to obtain a 2-site, 5-orbital Hubbard model.
• Compute interaction parameters via constrained RPA (cRPA).
• Apply FLEX to obtain spin-fluctuation mediated self-energies and solve the linearized Eliashberg equation to extract the eigenvalue λ as a measure of proximity to superconductivity.
• Identify superconducting gap symmetry (s±) from the leading Eliashberg eigenfunction.
• Analyze how ∆E and incipient-band conditions influence the pairing strength and structure.

Experimental results

Research questions

• RQ1 Can hole-doped La3Ni2O6 realize an OSBM superconducting state with incipient bands?
• RQ2 How does the orbital-level offset ∆E between dx2−y2 and other Ni-d orbitals affect superconductivity in La3Ni2O6?
• RQ3 What is the symmetry and origin of the superconducting gap in OSBM for La3Ni2O6 under realistic first-principles band structures?
• RQ4 To what extent do interorbital interactions (beyond dx2−y2–d3z2−r2) contribute to OSBM superconductivity?
• RQ5 How do structural type (T vs T′) and external pressure or chemical substitution influence structural stability and the OSBM pairing tendency?

Key findings

• Superconductivity in OSBM is enhanced in the incipient-band regime where one band is near the Fermi level while another touches or lies near the band edge.
• Hole doping drives La3Ni2O6 into an incipient-band regime and yields an s±-wave gap with sign change between the dx2−y2 band and the lower (other d) bands.
• The leading eigenvalue λ of the linearized Eliashberg equation increases with hole doping, with largest values around n≈8.1–8.4 depending on structure and method (GGA vs GGA+U).
• Interorbital interactions, particularly between dx2−y2 and t2g/eg sets, play a key role in enhancing OSBM superconductivity, with OSBM-dominant contributions evident in certain doping regimes.
• The T′ structure is energetically favored at ambient conditions, but hole doping and pressure can shift stability toward the T structure; dynamical stability is possible for both structures under suitable conditions.
• Phonon calculations indicate dynamical stability, and structural stability is sensitive to A-site substitutions and pressure, affecting the OSBM viability.