High-energy pseudogap in degenerate Hubbard model induced via Hund coupling

TL;DR

This paper demonstrates that Hund coupling in a five-band Hubbard model induces a stable pseudogap above the Fermi level, linked to spin fluctuations, with implications for iron pnictide optical spectra.

Contribution

It reveals a novel Hund coupling-induced pseudogap mechanism in a multiband Hubbard model using dynamical mean field theory.

Findings

Pseudogap appears due to a collective mode in the self-energy.

Pseudogap is stable across a wide parameter range.

Disappears with weak Hund coupling.

Abstract

Hund coupling in the degenerate five-band Hubbard model near n=6 occupancy is shown to give rise to a significant depletion of spectral weight above the Fermi level. Calculations within dynamical mean field theory combined with exact diagonalization reveal that this pseudogap is associated with a collective mode in the self-energy caused by spin fluctuations. The pseudogap is remarkably stable over a wide range of Coulomb and exchange energies, but disappears for weak Hund coupling. The implications of this phenomenon for optical spectra of iron pnictides are discussed.