Theoretical Investigation of Fermion Pairings in Three-band Extended Hubbard Model

TL;DR

This paper provides a theoretical analysis of fermion pairing in a three-band extended Hubbard model, revealing d-wave symmetry pairing, two-gap phenomena, and non-Fermi liquid behavior, aligning qualitatively with experimental observations.

Contribution

It introduces a separable inter-site interaction in the extended Hubbard model and explores its effects on fermion pairing and spectral gaps, emphasizing d-wave symmetry.

Findings

Fermion pairing occurs only for pure d-wave symmetry.

Two gaps appear in the normal state spectrum, related to spin and charge orderings.

Non-Fermi liquid behavior is predominant in the model.

Abstract

The two-dimensional d-p model (or extended Hubbard model) on a square lattice is investigated for fermion pairing by a slave boson method. The inter-site d-fermion interaction is introduced additionally. The momentum space counterpart of this interaction is taken to be separable and expanded in terms of basis functions corresponding to mixed symmetry states. The investigation leads to anomalous pairing of fermion fields only for pure d-wave symmetry. The charge and spin ordering gaps appear in the single- particle spectrum when d(x,y) state is taken into account.The non-Fermi liquid behavior is found to be the prevalent one generally. The study yields a good qualitative account of the nodal-antinodal dichotomy. Two gaps appear in the normal state spectrum; the larger one corresponds to the sum and the smaller to the difference of spin and charge ordering gaps. This two-gap scenario is in qualitative agreement with recent experimental finding.