Probing the Response of Two-Dimensional Crystals by Optical Spectroscopy

This thesis focuses on the study of the optical response of new atomically thin two-dimensional crystals, principally the family of transition metal dichalcogenides like MoS 2 . One central theme of the thesis is the precise treatment of the linear and second-order nonlinear optical susceptibilities of atomically thin transition metal dichalcogenides. In addition to their significant scientific interest as fundamental material responses, these studies provide essential knowledge and convenient characterization tools for the application of these 2D materials in opto-electronic devices. Another important theme of the thesis is the valley physics of atomically thin transition metal dichalcogenides. It is shown that the degeneracy in the valley degree of freedom can be lifted and a valley polarization can be created using a magnetic field, which breaks time reversal symmetry in these materials. These findings enhance our basic understanding of the valley electronic states and open up new opportunities for valleytronic applications using two-dimensional materials.

Nominated by Columbia University as an outstanding PhD Thesis Provides convenient characterization tools for atomically thin transition metal dichalcogenides and their application in opto-electronic devices Enhances our understanding of valley electronic states and opens up new opportunities for valleytronic applications using 2D materials Includes supplementary material: sn.pub/extras

Inhalt

Introduction and Background.- Intrinsic Doping Dependence of Raman 2D Mode in Graphene: Signatures of Electron-Electron Interaction.- Coupling of Strongly Localized Graphene Plasmons to Molecular Vibrations.- Dielectric Response of a Thin Sheet.- Measurement of the Optical Dielectric Function of Monolayer Transition Metal Dichalcogenides: MoS 2 , MoSe 2 , WS 2 , and WSe 2 .- Measurement of the Second-Order Nonlinear Susceptibility and Probing Symmetry Properties of Few-Layer MoS 2 and h-BN by Optical Second-Harmonic Generation.- Valley Splitting and Polarization by Zeeman Effect in Monolayer MoSe 2.- Conclusion and Prospect.