We investigate the near-field optical coupling between a single semiconductor nanocrystal (quantum dot) and a nanometer-scale plasmonic metal resonator using rigorous electrodynamic simulations. Our calculations show that the quantum dot produces a dip in both the extinction and scattering spectra of the surface-plasmon resonator, with a particularly strong change for the scattering spectrum. A phenomenological coupledoscillator model is used to fit the calculation results and provide physical insight, revealing the roles of Fano interference and hybridization. The results indicate that it is possible to achieve nearly complete transparency as well as enter the strong-coupling regime for a single quantum dot in the near field of a metal nanostructure.
In summary, we used rigorous electromagnetic simulations to calculate extinction and scattering spectra for a hybrid nanostructure consisting of a single semiconductor nanocrystal quantum dot and a metal-nanoparticle dimer. Because of the strong local field from the localized surface plasmon and the narrow transition linewidth of the QD at low temperature, a dramatic transparency dip appears in the broad plasmon resonance. This nearly complete transparency arises even though both structures are absorptive and even though the optical cross-section of the QD is five orders of magnitude lower than that of the metal nanostructure. This is possible because the excitation of plasmon resonances in the metal nanostructure strongly localizes electromagnetic fields at the position of the quantum dot, enhancing the coupling to the QD transition; this, in turn, leads to Fano interference and hybridization between the plasmon resonance and the QD transition. The transparency effect could be used in several applications, including the measurement of single-QD absorption spectra and the production of nanoscale plasmonic modulators.