Nonlinear optical response in two-dimensional Mott insulators

We theoretically examine the nonlinear optical responses in two-dimensional Mott insulators. The photoexcited states of the Mott insulators are described by an effective model in the strong-coupling limit of a half-filled Hubbard model. By comparing the linear optical absorption, nonlinear optical two-photon absorption and third harmonic generation (THG), we clarify the nature of photoexcited states such as the distribution of odd-parity and even-parity states. In the THG spectrum, main contribution is found to come from the process of three-photon resonance associated with the odd-parity states. As a result, the two-photon resonance process is less pronounced in the THG spectrum. The calculated THG spectrum is qualitatively consistent with recent experimental data