# Doublon-holon origin of the subpeaks at the Hubbard band edges

## TL;DR

This paper explains the origin of subpeaks at the Hubbard band edges in the spectral function of the SU(2) Fermi-Hubbard model near the Mott transition, attributing them to doublon-holon pair interactions, supported by DMFT and mean-field analysis.

## Contribution

It identifies the doublon-holon pairs as the origin of subpeaks and demonstrates this through combined DMFT and mean-field approaches, extending understanding to SU(3) and SU(4) models.

## Key findings

- Subpeaks originate from doublon-holon pair interactions.
- Mean-field results agree with DMFT calculations.
- Subpeaks are more pronounced in SU(3) and SU(4) models.

## Abstract

Dynamical mean-field theory (DMFT) studies frequently observe a fine structure in the local spectral function of the SU(2) Fermi-Hubbard model at half filling: In the metallic phase close to the Mott transition, subpeaks emerge at the inner edges of the Hubbard bands. Here we demonstrate that these subpeaks originate from the low-energy effective interaction of doublon-holon pairs, by investigating how the correlation functions of doublon and holon operators contribute to the subpeaks. A mean-field analysis of the low-energy effective Hamiltonian provides results consistent with our DMFT calculation using the numerical renormalization group as an impurity solver. In the SU(3) and SU(4) Hubbard models, the subpeaks become more pronounced due to the increased degeneracy of doublon-holon pair excitations.