High-order harmonic spectroscopy of two-dimensional quantum materials

Abstract

High-order harmonics (HH) are generated by a non-linear optical process with the interaction of a target and intense laser pulse. HH generation is a powerful tool to generate ultrafast light source from ultraviolet (UV) to extreme ultraviolet (XUV) region. In addition, HH can be used as a probe of material properties like band structure, Berry curvature, or topological class. In this thesis, we study the light-matter interaction in two-dimensional materials, mainly with HH. Especially, we focus on special quantum materials such as Chern insulators and topological insulators. For the first part of the thesis, we study the light-matter interaction in topological materials. We check and validate whether HH can be used as a probe of the topological class of the material. In addition, the light-matter interaction in topological materials is studied with the anomalous Hall conductivity (AHC). The counter-rotating bicircular laser field is used to excite the valley of the trivial and topological insulators, and the reaction of the system is studied using AHC. Semiclassical analysis, using the stationary phase approximation, is applied to understand the dynamics of the HH generation in topological materials. We also study the semiconductor Bloch equations (SBEs) in the velocity gauge and show that the velocity gauge can be used to avoid the wavefunction gauge problem in topological materials. For the second part of the thesis, we focus on the HH in real materials. HH in monolyaer and bilyaer 2D materials, such as MoS2 and hBN, is studied. The effect of the interlayer coupling on the HHG is studied for the two materials.