Nonlinear optical response and spin-charge separation in one-dimensional Mott insulators

We theoretically study the nonlinear optical response and photoexcited states of the Mott insulators. The nonlinear optical susceptibility chi((3)) is calculated by using the exact diagonalization technique on small clusters. From the systematic study of the dependence of chi((3)) on dimensionality, we find that the spin-charge separation plays a crucial role in enhancing chi((3)) in the one-dimensional (1D) Mott insulators. Based on this result, we propose a holon-doublon model, which describes the nonlinear response in the 1D Mott insulators. These findings show that the spin-charge separation will become a key concept of optoelectronic devices.