Source capture
Authors Evgeny A. Stepanov, Steffen Bötzel, Ilya M. Eremin, Frank Lechermann
arXiv / Publisher http://arxiv.org/abs/2604.08221v1
PDF https://arxiv.org/pdf/2604.08221v1
Relevance score 5.034
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Research paradigm Theoretical
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Summary

Based on the effective three-orbital model, this study systematically analyzes the interplay between multiorbital and nonlocal self-energy effects in the normal state of the high-pressure superconducting bilayer nickelate La3Ni2O7 using the D-TRILEX many-body framework beyond dynamical mean-field theory. The results reveal that the low-energy physics is highly dependent on the interorbital interaction strength: when the interaction is weak, the renowned γ quasiparticle flat band lies below the Fermi level; as the interaction strengthens, this flat band crosses the Fermi level, causing electrons to scatter with ferromagnetic paramagnon excitations, thereby forming spin-polaron bound states. These bound states manifest as incoherent spectral weight shadow bands below the Fermi level. The findings unveil the existence of additional competing electronic states in bilayer nickelates, providing a theoretical basis for resolving recent controversies in angle-resolved photoemission spectroscopy experiments regarding spectral structures near the Fermi surface.

Materials

Methods

Keywords

Highlights

  • The low-energy physics is highly dependent on the interorbital interaction strength.
  • The findings provide a theoretical basis for resolving ARPES controversies regarding spectral structures near the Fermi surface.

Conclusions

  • When the interorbital interaction is strong, the flat γ band crosses the Fermi level, and electrons scatter with ferromagnetic paramagnon excitations, forming spin-polaron bound states.
  • These bound states manifest as incoherent spectral weight shadow bands below the Fermi level.

Main claims

  • In La3Ni2O7, the position of the flat γ band relative to the Fermi level is controlled by interorbital interaction strength
    • Evidence: D-TRILEX calculations show that increasing U2 reduces occupation of the γ band, shifting its flat part upward; at U2=4.6 eV the flat band is exactly at Fermi level
  • When the flat band crosses the Fermi level, electrons scatter with ferromagnetic spin fluctuations, forming spin-polaron bound states that appear as incoherent shadow bands
    • Evidence: The self-energy becomes strongly momentum-dependent near M point; spin susceptibility shows FM-like character; a shadow band appears below Fermi level

Workflow

  • Model and method setup — Low-energy physics depends on U2
    • Materials: Effective three-orbital model for La3Ni2O7
    • Methods: D-TRILEX method incorporating nonlocal correlations beyond DMFT
    • Observations: Spectral function, self-energy, susceptibilities
  • Analysis of results — Spin-polaron bound states form from scattering with ferromagnetic paramagnon excitations
    • Methods: Analytic continuation; Bethe-Salpeter eigenvalues
    • Observations: For smaller U2, flat dz2 band below Fermi level; for larger U2, flat band crosses Fermi level leading to spin-polaron formation