Harvesting Excitons through Plasmonic Strong Coupling

Light-generated excitons play a key role in many relevant processes. A large research effort is directed towards controlling the properties of exciton transport inside different materials, both for fundamental reasons and for device improvement purposes. A recent work [1] has shown that the exciton conductance along a linear chain of organic molecules inside a cavity can be boosted by several orders of magnitude when the so-called Strong Coupling (SC) regime is achieved. Among different proposals, surface plasmons have been considered as good candidates for achieving this regime due to their great field enhancement [2]. Motivated by these promising results, we study the exciton conductance in a system of quantum emitters located near a plasmonic NS. The conductance is shown to increase largely when the SC regime is achieved between the emitters and the NS localized surface plasmons (LSP). Moreover, we demonstrate that the transport efficiency is position-dependent, being very high for pole-to pole transport and very low for pole-to-equator transport. This directionality is due to the inhomogeneous field profile of the LSP, which directs the excitation towards the zones of higher electric field intensity. In a second part, we try to exploit this result for enhancing the pole-to-pole transport efficiency. In order to achieve this, we place two extra spheres very close to the north and south pole of the original NS, so that the field in the gap region is largely enhanced. We show how, by pumping an emitter in one of the gaps, the excitation is transferred very efficiently to the second gap. Thus, this simple nanostructure not only allows a strongly enhanced exciton conductance, but also to route the exciton to a targeted and very narow region of space. This is a very suggestive result for potential applications such as photovoltaics, in which the localization of excitons in a small region could largely increase the efficiency of devices.

References

[1] Johannes Feist and F.J. Garcia-Vidal, Phys. Rev. Lett (Accepted, 3 November 2014).

[2] J. Bellessa, C. Bonnand, J.C. Plenet, and J. Mugnier, Phys. Rev. Lett. 93, 036404 (2004).

carlos.ballestero@uam.es