Source capture
Authors Huimei Liu, Giniyat Khaliullin
arXiv / Publisher https://arxiv.org/abs/2602.23989
PDF https://arxiv.org/pdf/2602.23989
Relevance score 5.218
Primary category cond-mat.str-el
Published 2026-03-24
Research paradigm Theoretical
Sample form Unknown

Summary

This study constructs a microscopic theoretical model for the superconducting gap structure of bilayer nickel oxides, where a conduction band with dx2-y2 symmetry coexists with localized d3z2-r2 spins. Strong interlayer coupling leads to a singlet ground state of local magnetic moments, whose virtual singlet-triplet excitations (i.e., "triplons") mediate pairing interactions between conduction electrons, thereby generating interband s±-wave pairing with opposite signs of the order parameters on the two bands (α and β). The theoretical results naturally explain key experimental observations: despite the smaller density of states of the α band, its superconducting gap is larger, and the gap exhibits significant momentum-space anisotropy arising from nonlocal Kondo coupling. These findings strongly support the triplon-mediated pairing mechanism as the microscopic origin of superconductivity in bilayer nickel oxides.

Materials

Methods

Keywords

Highlights

  • Provides a microscopic mechanism for the observed gap hierarchy in bilayer nickelates.
  • Triplon-mediated pairing naturally accounts for key features seen in STM and ARPES.
  • Offers resolution to the debate on pairing mechanism in bilayer nickelates.

Conclusions

  • Strong interlayer coupling drives local moments into a singlet ground state; virtual singlet-triplet excitations (triplons) mediate pairing.
  • This yields interband s±-wave pairing with opposite signs on the α and β bands.
  • The theory explains the larger gap on the α band despite its smaller DOS, and pronounced gap anisotropy from nonlocal Kondo coupling.
  • The calculated tunneling spectra reproduce experimental two-gap features.

Main claims

  • Triplon-mediated pairing yields interband s±-wave superconductivity with larger gap on α band despite smaller density of states
    • Evidence: From abstract: 'This yields interband s± pairing, with opposite signs of the order parameter on the two (α and β) bands. Our theory naturally explains the key experimental features: a larger gap on the α band despite its smaller density of states'
  • Pronounced gap anisotropy arises from nonlocal Kondo coupling
    • Evidence: From abstract: 'pronounced gap anisotropy arising from nonlocal Kondo coupling'
  • Results support triplon-mediated pairing as microscopic origin of superconductivity in bilayer nickelates
    • Evidence: From abstract: 'The results support triplon-mediated pairing as the microscopic origin of superconductivity in bilayer nickelates'

Workflow

  • model_construction — Localized dz2 spins form interlayer singlet ground state; triplon excitations mediate pairing
    • Materials: Bilayer nickelate films
    • Methods: Tight-binding model for dx2-y2 and dz2 orbitals; Triplon theory for local spins
    • Observations: Band dispersions; Fermi surface with α and β bands
  • bcs_mean_field_analysis — Interband s±-wave pairing with larger gap on α band despite smaller DOS
    • Materials: Effective pairing Hamiltonian from triplon exchange
    • Methods: BCS mean-field theory
    • Observations: Superconducting gaps on α and β bands; Gap anisotropy
  • comparison_with_experiment — Theory reproduces experimental STM spectra
    • Materials: Calculated gaps
    • Methods: Simulation of tunneling spectra
    • Observations: Two-gap structure in spectra