Nonlinear optics in the electron-hole continuum in 2D semiconductors:two-photon transition, second harmonic generation and valley current injection

• 来源期刊: 科学通报（英文版）
• 年，卷（期）: 2019,（15）
• 页码范围: 1036-1043
• 页数: 8页
• 语种: 英文

摘要

We investigate two-photon transitions to the electron-hole scattering continuum in monolayer transition-metal dichalcogenides,and identify two contributions to this nonlinear optical process with opposite circularly polarized valley selection rules.In the non-interacting limit,the competition between the two contributions leads to a crossover of the selection rule with the increase of the two-photon energy.With the strong Coulomb interaction between the electron and hole,the two contributions excite electron-hole scattering states in orthogonal angular momentum channels,while the strength of the transition can be substantially enhanced by the interaction.Based on this picture of the two-photon transition,the second harmonic generation (SHG) in the electron-hole continuum is analyzed,where the Coulomb interaction is shown to greatly alter the relative strength of different cross-circular polarized SHG processes.Valley current injection by the quantum interference of one-photon and two-photon transition is also investigated in the presence of the strong Coulomb interaction,which significantly enhances the injection rate.