Spontaneous surface plasmon polariton decay of band-edge excitons in quantum dots near a metal surface

Surface plasmon polaritons (SPPs) due to their subwavelength nature could significantly modify electronic transition behaviors in various optoelectronic systems. Here, using a model system with a spherical quantum dot (QD) close to a flat metal surface, we show that the conventional forbidden optical transitions in a QD could be largely enabled by the spontaneous SPP decay. The electronic states of the QD are approximated by a Bloch state combined with wave functions in a spherical potential well, which provides multiple hole states with mixed electronic multipoles. Moreover, the SPP is quantized by using a canonical quantization scheme followed by a Green's function approach to introduce its dissipation. In particular, we find that when the SPP dissipation is included, the spontaneous decay of the corresponding QD exciton is dominant by the transition into the off-resonance mode of SPPs with large momenta. Also, we have studied the dependence of spontaneous decay rates on the size and crystal orientation of a QD, the distance between the QD and metal surface, and the linewidth of SPPs. Some useful scaling relations have been revealed, and the multipole transitions are found to be comparable with the dipole transition under specific system parameters. These findings have important implications for our understanding of the electronic transition at a metal near field and might prove instrumental for the future design of plasmonic and QD devices.