In a joint study with the Polytechnic University of Milan, we have measured how fast it takes for exciton states to form after high-energy optical excitation in the 2D semiconductor single-layer MoS2. In semiconductors, excitons consist of negatively-charged electrons that are coulombically bound to positively-charged holes and form excited states that have quantum properties that mirror those of a hydrogen atom. But how long does it take for an unbound electron and unbound hole to bind to form an exciton? In this study, we investigate that question in collaboration with the team from Italy using ultrafast laser spectroscopy. From these studies we find that the exceptionally strong coulomb interactions in 2D materials leads to ultrafast exciton formations times of 40 femtoseconds, which is 40 one millionths of one billionth of a second! This formation time is substantially shorter than bulk semi
More information is available from Nature Communications:
"The ultrafast onset of exciton formation in 2D semiconductors"
Trovatello, C. et al.
Nature Communications doi:10.1038/s41467-020-18835-5 (2020).
http://www.nature.com/articles/s41467-020-18835-5