Photoinduced absorptions inside the Mott gap in the two-dimensional extended Hubbard model

TL;DR

This paper theoretically studies the ultrafast optical responses in a two-dimensional extended Hubbard model, revealing photoinduced absorptions inside the Mott gap and the roles of Coulomb interactions and doping.

Contribution

It introduces a detailed analysis of photoinduced phenomena in the extended Hubbard model, highlighting biexcitonic effects and the influence of Coulomb interactions on optical responses.

Findings

Photoinduced absorptions appear inside the Mott gap upon pumping.

The spectral weight below the Mott gap increases as the on-site Coulomb interaction decreases.

Next-nearest-neighbor Coulomb interaction enhances the U dependence, indicating biexcitonic contributions.

Abstract

We theoretically investigate pump-probe optical responses in the two-dimensional extended Hubbard model describing cuprates by using a time-dependent Lanczos method. At half filling, pumping generates photoinduced absorptions inside the Mott gap. A part of low-energy absorptions is attributed to the independent propagation of photoinduced holons and doublons. The spectral weight just below the Mott gap increases with decreasing the on-site Coulomb interaction $U$. We find that the next-nearest-neighbor Coulomb interaction $V_1$ enhances this $U$ dependence, indicating the presence of biexcitonic contributions formed by two holon-doublon pairs. Photo-pumping in hole-doped systems also induces spectral weights below remnant Mott-gap excitations, being consistent with recent experiments. The induced weights are less sensitive to $V_1$ and may be related to the formation of a biexcitonic state in the presence of hole carriers.