Excitonic effect on optical response in one-dimensional two-band Hubbard model

TL;DR

This paper investigates the excitonic effects on the optical response of a one-dimensional two-band Hubbard model, revealing how intersite Coulomb interactions induce excitonic states consistent with experimental spectra.

Contribution

It demonstrates that excitonic states caused by intersite Coulomb repulsion significantly influence optical responses in a one-dimensional two-band Hubbard model, aligning with experimental observations.

Findings

Low-energy peak is Lorentzian due to excitonic state

Intersite Coulomb repulsion induces excitonic states

Localization of holes leads to exciton formation

Abstract

Motivated by the gigantic nonlinear optical response in the halogen-bridged Ni-compounds, the underlying electronic states of the compounds are examined in the one-dimensional two-band Hubbard model, by studying the current-current correlation function and the charge density in the ground state. The dynamical density matrix renormalization group method is employed. We find that the low-energy peak of the correlation function consists of a single Lorentzian component for a parameter range appropriate to the compounds. This is due to an excitonic state induced by the intersite Coulomb repulsion between holes on the metal and halogen ions. This is consistent with the optical absorption spectra of the compounds. We suggest that the localization of holes on the metal ions in the ground state brings about the formation of the excitonic state.