Charge correlation, doublon-holon binding and screening in the doped Hubbard model

TL;DR

This paper investigates how electronic correlations, doublon-holon binding, and screening effects evolve in the doped Hubbard model, revealing new exciton complexes and implications for modeling correlated materials.

Contribution

It introduces the emergence of exciton complexes like holon-doublon-holon trions upon doping and discusses their impact on screening and modeling of correlated materials.

Findings

Emergence of holon-doublon-holon trions in doped systems

Enhanced screening due to collective excitations

Different effective U values needed for doped and parent compounds

Abstract

Electronic correlations arise from the competition between the electrons' kinetic and Coulomb interaction energy and give rise to a rich phase diagram and many emergent quasiparticles. The binding of doubly-occupied and empty sites into a doublon-holon exciton is an example of this in the Hubbard model. Unlike traditional excitons in semiconductors, in the Hubbard model it is the kinetic energy which provides the binding energy. Upon doping, we find the emergence of exciton complexes, such as a holon-doublon-holon trion. The appearance of these low-lying collective excitations make screening more effective in the doped system. As a result, Hubbard-based modelling of correlated materials should use different values of $U$ for the doped system and the insulating parent compound, which we illustrate using the cuprates as an example.