Supertransport of excitons in atomically thin organic semiconductors at the 2D quantum limit.

Long-range and fast transport of coherent excitons is important for the development of high-speed excitonic circuits and quantum computing applications. However, most of these coherent excitons have only been observed in some low-dimensional semiconductors when coupled with cavities, as there are large inhomogeneous broadening and dephasing effects on the transport of excitons in their native states in materials. Here, by confining coherent excitons at the 2D quantum limit, we first observed molecular aggregation-enabled ‘supertransport’ of excitons in atomically thin two-dimensional (2D) organic semiconductors between coherent states, with a measured high effective exciton diffusion coefficient of ~346.9 cm2/s at room temperature. This value is one to several orders of magnitude higher than the values reported for other organic molecular aggregates and low-dimensional inorganic materials. Without coupling to any optical cavities, the monolayer pentacene sample, a very clean 2D quantum system (~1.2 nm thick) with high crystallinity (J-type aggregation) and minimal interfacial states, showed superradiant emission from Frenkel excitons, which was experimentally confirmed by the temperature-dependent photoluminescence (PL) emission, highly enhanced radiative decay rate, significantly narrowed PL peak width and strongly directional in-plane emission. The coherence in monolayer pentacene samples was observed to be delocalised over ~135 molecules, which is significantly larger than the values (a few molecules) observed for other organic thin films. In addition, the supertransport of excitons in monolayer pentacene samples showed highly anisotropic behaviour. Our results pave the way for the development of future high-speed excitonic circuits, fast OLEDs, and other optoelectronic devices. Scientists have detected excited quasi-particles, called excitons, moving far and fast in a two-dimensional organic semiconductor, paving the way for applications in quantum computing and fast light emitting diodes. Yuerui Lu of the Australian National University and colleagues conducted tests in a 2D sample of pentacene, an organic semiconducting compound made of benzene rings fused into a chain. Light particles are absorbed by pentacene, generating excitons that can be used to develop tiny, very fast, energy-efficient optoelectronic devices. The team found that excitons move through the crystal depending on the temperature and pentacene’s molecular arrangements and order of crystallinity. The long-range and fast migration of excitons in a monolayer of pentacene was at least an order of magnitude higher than in other materials. The excitons in the pentacene monolayer also generated sharp, strong ‘superradiant’ light emissions.