Strain-modulated band structure and high harmonic generations in two-dimensional MoS2

Abstract

Two-dimensional (2D) condensed matter is a material that is restricted in one direction while being periodic in the other. Since the restricted size of 2D materials is comparable to the wavelength of electrons, a quantum confinement effect may occur. Moreover, the absence of periodicity provides weak screening in 2D materials, which brings novel physical properties such as the quantum well, which is widely applied in quantum information, and the fine absorption structures in graphene. Among the 2D materials, the monolayer transition metal chalcogenides represented by MoS2 have attracted wide attention due to the direct band gap in the visible light region (1.8 eV) and valley polarizations, which are prospective for solar cells as well as photoelectric devices. High-harmonic generation (HHG) is a strong non-linear process during which a high-energy laser impulse is applied to materials and high-harmonic radiations are yielded. As a typical ultrafast dynamic, HHG has important applications in laser generation, such as EUV lithographic metrology and high-resolution coherent imaging. According to the Bloch oscillation model, HHG is highly dependent on band structure. Here, we report the strain-dependent HHG dynamics in MoS2. Further investigation reveals that the strain-dependence of HHG is caused by band modulation under different strains, which is dominant during HHG. Our research sheds light on ways to achieve effective modulations in ultrafast dynamics, implying an all-optical measurement band structure in strained materials.