Abstract
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.
Highlights
The transmission electron microscopy (TEM) images of the synthesized WS2 monolayer quantum disks (MQDs) with carrier density (p) of 0.6(±0.2) × 1012 cm−2, 3.0(±0.2) × 1012 cm−2, and 8.3(±0.2) × 1012 cm−2 are shown in Supplementary Fig. S1, which exhibit monodispersed distribution with an average size of ~5.0 ± 1.0 nm
1234567890():,; microscopy (AFM) of the WS2 MQDs was performed to characterize the height profile of the synthesized WS2 MQDs and the result is displayed in Supplementary Fig. S3
Two peaks at around 3.21 ± 0.02 and 3.73 ± 0.02 eV were observed in the absorption spectrum, and their energies are in agreement with those of the previously reported WS2 MQDs (3.15 and 3.72 eV).[11]
Summary
Due to the reduced dielectric screening and relatively heavy particle band masses, few-layered transition-metal dichalcogenide (TMDs) form tightly bound electron–hole pairs (excitons) with binding energies up to hundreds of meV, which is much larger than that in conventional bulk semiconductors.[1,2,3] The strongly bound excitons produce a variety of interesting multiparticle excitations such as charged excitons (trions), biexcitons, and exciton–trion complexes.[3,4,5] Because of efficient Coulomb interactions, few-layered TMDs are strongly interacting systems even in high carrier densities, they provide an ideal vehicle to study fundamental many-body physics, such as band-gap renormalization and the Mott transition.[2,6,7,8]. On the basis of carrier screening, we discuss the mechanism that causes the carrier-induced band-gap renormalization and the reduced exciton binding energies
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