Studies of spatial- and momentum-indirect excitons in two-dimensional semiconductors and relevance to exciton condensation

Bose-Einstein condensate of excitons has been an intense interest in solid-state materials, especially upon the discovery of two-dimensional semiconducting materials. This PhD thesis is an experimental study of spatial- and momentum-indirect excitons using WSe2 and InSe, which is twofold. The study of spatial-indirect excitons achieves desirable electrical contacts to the two-dimensional semiconductor transistors, which paves the way to explore exciton condensate in electrical transport measurements. In addition, the study of momentum-indirect excitons brings the serendipitous finding of efficient upconversion photoluminescence, which provides important implications for exciton condensation.