Nonlinear optical response in Mott insulators

We theoretically study nonlinear optical response and photoexcited states of the Mott insulators in one dimension (1D). We find that the spin-charge separation and large on-site Coulomb interaction play a crucial role in obtaining degenerate dipole-allowed and dipole-forbidden states in the photoexcited states. Based on this result, we propose a holon–doublon model. The calculated nonlinear optical susceptibilities reproduce experimental data very well for 1D insulating cuprates.