Engineering exciton many-body interaction in atomically thin MoS2

Abstract

Atomically thin transition metal dichalcogenides (TMDCs) have emerged as a leading semiconductor over the past decades due to their exceptional electronic, optoelectronic and quantum properties. Here, we have studied tuning of optical and electronic properties in CVD grown single- and few-layer MoS2 by employing spectrally and temporarily resolved ultrafast transient absorption (TA) spectroscopy. By doing pump-fluence dependent measurement, we observed different optical response in two extreme fluence regimes. In the high pump-fluence regime above some critical carrier density, the system undergoes a transition from an excitonic bound state to the electron-hole plasma state, which is termed as Mott-transition. Our experimental findings show a drastic change in optical response in the very high pump fluence, which demonstrate a large bandgap renormalization of around 300 meV. Further, we have fitted TA for A and B exciton and found that both exciton energies red shifting with increasing pump fluence. These results indicate that atomically thin MoS2 can be a promising material for phototransistors, quantum information processing, sensors, and light-harvesting devices.