Anomalous Dipole–Dipole Interaction in an Ensemble of Quantum Emitters and Metallic Nanoparticle Hybrids

Abstract

We have developed a theory for the photoluminescence (PL) and scattering cross section of a core–shell hybrid, where the core is the metallic nanoparticle and the shell is made of an ensemble of quantum emitters. A probe field is applied to calculate the scattering cross section of the core–shell hybrid. The surface plasmon polariton field in the metallic nanoparticle is calculated by solving the Maxwell equations in the quasi-static approximation. Dipoles are induced in the ensemble of quantum emitters because of the probe field and surface plasmon polariton field. Therefore, the dipole of one quantum emitter interacts with dipoles of other quantum emitters in the ensemble, and hence, there is the dipole–dipole interaction (DDI) between quantum emitters. We discovered an anomalous DDI, which is induced by the surface plasmon polaritons. It is shown that the strength of the DDI can be controlled by the surface plasmon polariton frequency, and it plays a dominant role in the phenomenon of the PL and scattering cross section. The surface plasmon polariton field can also interact with excitons of the quantum emitters via the exciton-surface plasmon polariton interaction. Using the density matrix method, the PL and scattering cross section are evaluated. It is found that the spectrum of the PL and the scattering cross section splits from one peak into two peaks mainly because of the strong coupling between the excitons and anomalous DDIs. It means that the PL and scattering spectrums can be switched ON (one peak) and OFF (two-peaks). This finding is consistent with the experimental data of the PL and scattering cross section of the J-aggregate and silver core–shell hybrid. We have found that the splitting and height of the two peaks can be increased or decreased by controlling mainly the strength of the anomalous DDI. The anomalous DDIs can be controlled by applying an external pulse pressure and pulse control laser. Hence, the present findings can be used for fabricating nanosensors and nanoswitches for applications in nanotechnology and nanomedicines.