Coherent Terahertz Wave Generation from Mono- and Multilayer MoS 2 through Quantum Interference

Quantum interference (QI) has been widely studied in advanced materials and can be exploited to control the nonlinear response by varying the relative phase between the incident optical pulses. However, the contribution of the coherent injected photocurrent by QI from the indirect gap materials is still unclear because of the much weaker phonon-assisted absorption compared with that from the direct gap materials. Here, we investigate the coherent injected photocurrent in mono- and multilayer MoS 2 with thickness at the nanometer scale under 2-color light excitation by detecting the generated coherent terahertz (THz) wave. We observe that the THz radiation can be controlled by the relative phase. Besides, we obtain similar experimental results of the THz wave generation from mono- and multilayer MoS 2 when we change the relative polarization angle between 𝜔 and 2𝜔 pulses, in comparison to the case of direct gap materials. Thus, these experimental results further verify that, in multilayer MoS 2 with an indirect gap, QI in the direct gap region is the dominant process for the THz wave generation. Furthermore, we demonstrate that QI can be a more effective mechanism to induce THz radiation than optical rectification under single-color light excitation. This study enhances the understanding of QI in indirect gap materials and highlights the potential of 2-color light excitation for investigating third-order nonlinear processes in advanced materials.