Two-dimensional (2D) material is the thinnest material humans have ever made. It has only one or a few atoms in thickness, which is one million times thinner than a piece of paper. The successful isolation and manipulation of atomically thin 2D materials have ushered in a new era of fundamental scientific research and technological innovation. Since the discovery of graphene, an ever-growing class of 2D materials has been identified to exhibit extraordinary properties distinctive from their bulk counterparts. For example, monolayers of materials such as those in the transition metal dichalcogenide (TMDC) family exhibit direct band gaps, strong light-matter interactions, access to the valley degree of freedom, and largely reduced Coulomb screening, which has triggered a lot of interest in electronic and optoelectronic applications.
So far, optical spectroscopy has been an indispensable tool for characterizing 2D materials. For example, we have utilized ultrafast nonlinear optical spectroscopies to reveal the crystal and electronic structure of TMDCs. In the future, we are interested in developing novel scanning near-field optical microscopy techniques to interrogate the material's intrinsic many-body response with subdiffractional resolution. Moreover, we plan to leverage the extreme thickness of 2D materials and the ultra-strong field within the laser light to coherently control the material's physical properties, such as the valley and topological degrees of freedom in the electronic bandstructure.