The emergence of two-dimensional transition metal dichalcogenide (TMDC) materials, in combination with their twist structures, has revolutionized the field of materials science by offering a remarkable degree of flexibility in fabricating heterostructures and twist homo-bilayers using a tear-stack process. These novel structures exhibit a moiré superlattice configuration, which introduces intriguing characteristics and opens new avenues for exploring fundamental physical phenomena.

In this chapter, we provide an overview of the structure of TMDC material and twist bilayer system. We firstly introduce the intricate details of the band structure, exciton in TMDC materials and significant experimental characterization of excitonic states. Moreover, we focus on the observed optical properties of twist bilayer system including the formation of interlayer excitons and the influence of the moiré superlattice. Finally, we present experimental outcomes related to the twist WSe2 system, shedding light on the fascinating phenomena observed in this particular twist bilayer system. This comprehensive exploration aims to enhance our knowledge of the distinct characteristics of TMDC material and provide assistance and guidance for analyzing the twist bilayer WSe2 system.