Two-layered molybdenum disulfide is a van der Waals material, where electrons can be excited using a suitable experimental setup. These electrons later leave their position in the valence band, leaving behind a positively charged hole, and enter the conduction band.
Because electrons and holes have differing charges, they are attracted to one another and combine to form a quasiparticle. The latter can move freely within the material and is also known as an electron-hole pair or exciton.
Excitation with light results in two different kinds of electron-hole pairs in two-layered molybdenum disulfide: intralayer pairs, where the electron and hole are localized in the same layer of the material, and interlayer pairs, where the electron and hole are located in different layers and are thus spatially apart.
These two varieties of electron-hole couples exhibit various characteristics. Light and intralayer couples interact aggressively, causing them to glow intensely. On the other hand, interlayer excitons are considerably weaker but may be moved to different energies, allowing scientists to adjust the absorbed wavelength. Interlayer excitons, like intralayer excitons, have extremely potent, nonlinear interactions with one another. These interactions are crucial to many of the applications that interlayer excitons could serve.
Now, the researchers from the group led by Professor Richard Warburton of the Department of Physics and the Swiss Nanoscience Institute (SNI) of the University of Basel have coupled these two types of electron-hole pairs by bringing the two of them to similar energies.
This was possible due to adjusting interlayer excitons. The resulting coupling causes the properties of the two types of electron-hole pairs to merge, allowing scientists to tailor merged particles that are not only very bright but also interact very strongly.
Lukas Sponfeldner, a doctoral student at the SNI Ph.D. School and the first author of the paper told Phys.org, “This allows us to combine the useful properties of both types of electron-hole pairs. These merged properties could be used to produce a novel source of individual photons, which are a key element of quantum communication.”
Scientists have also shown that this complex system of electron-hole pairs can be simulated using classical models from the fields of mechanics or electronics.
Professor Richard Warburton said, “Specifically, electron-hole pairs can be very effectively described as oscillating masses or circuits. These simple and general analogies help us better understand the fundamental properties of coupled particles, not only in molybdenum disulfide but also in many other material systems and contexts.”