Many-body effects in doped WS 2 monolayer quantum disks at room temperature

Due to strong Coulomb interactions, reduced screening effects, and quantum confinement, transition-metal dichalcogenide (TMD) monolayer quantum disks (MQDs) are expected to exhibit large exciton binding energy, which is beneficial for the investigation of many-body physics at room temperature. Here, we report the first observations of room-temperature many-body effects in tungsten disulfide (WS2) MQDs by both optical measurements and theoretical studies. The band-gap renormalization in WS2 MQDs was about 250 ± 15 meV as the carrier density was increased from 0.6(±0.2) × 1012 to 8.3(±0.2) × 1012 cm−2. We observed a striking exciton binding energy as large as 990 ± 30 meV at the lowest carrier density, which is larger than that in WS2 monolayers. The huge exciton binding energy in WS2 MQDs is attributed to the extra quantum confinement in the lateral dimension. The band-gap renormalization and exciton binding energies are explained using efficient reduced screening. On the basis of the Debye screening formula, the Mott density in WS2 MQDs was estimated to be ~3.95 × 1013 cm−2. Understanding and manipulation of the many-body effects in two-dimensional materials may open up new possibilities for developing exciton-based optoelectronic devices.