Conserving approximation for the three-band Hubbard model: flat quasiparticle dispersion

TL;DR

This paper demonstrates that a conserving approximation accurately reproduces the flat quasiparticle dispersion observed in experiments and Quantum Monte Carlo data for the three-band Hubbard model at certain doping levels.

Contribution

It introduces a conserving approximation framework that self-consistently includes interactions with charge, spin, and two-particle fluctuations to model quasiparticle dispersion.

Findings

Quasiparticle dispersion is flat near $(\pi,0)$ and $(0,\pi)$ points.

Spin-fluctuations significantly reduce quasiparticle dispersion near the Fermi energy.

The results align with angle-resolved photoemission measurements.

Abstract

It is shown that the low-energy single-particle excitation-spectrum of the three-band Hubbard model at hole-dopings away from half-filling agrees remarkably well with Quantum Monte Carlo data and spectroscopic experiments within the framework of a conserving approximation that includes self-consistently the interaction with charge, spin, and two-particle fluctuations. The dispersion of the quasiparticle-peak obtained from the spectral-weight function is flat around the $(\pi,0)$ and $(0,\pi)$ points as has been observed in recent angle-resolved photoemission measurement. The significant reduction of the quasiparticle-dispersion near the Fermi-energy is due to spin-fluctuations, rather than being induced by band effects.