Abstract :

Optical properties of transition metal dichalcogenides monolayers are governed by the Wannier-Mott excitons forming a series of 1s, 2s, 2p, … hydrogen-like states. The excited excitonic states play important role in the nonlinear optical properties such as two-photon absorption and second harmonics generation. Here we present the theory of the excited excitonic states energy spectrum fine structure. We demonstrate that p- and s-shell excitons are mixed due to the specific D3h point symmetry of the transition metal dichalcogenides monolayers. Hence, both s- and p-shell excitons are simultaneously active in single- and two-photon processes providing an efficient mechanism of the second harmonic generation. The corresponding contribution to the nonlinear susceptibility is calculated.

Contact : denis.basko@lpmmc.cnrs.fr