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

We theoretically investigate pump-probe optical responses in a 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 holon and doublon. 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 V₁ 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 experiment. The induced weights are less sensitive to V₁ and may be related to formation of a biexcitonic state in the presence of hole carriers.