Absorption Reduction of Large Purcell Enhancement Enabled by Topological State-Led Mode Coupling

We propose the mechanism of edge state-led mode coupling under topological protection; i.e., localized surface plasmons almost do not have any influence on the edge state, while the edge state greatly changes the local field distribution of surface plasmons. Based on this mechanism, in the well-designed topological photonic structure containing a resonant plasmon nanoantenna, an obvious absorption reduction in the spontaneous emission spectra appears due to the near-field deformation around the antenna induced by the edge state. Because a plasmon antenna with ultrasmall mode volume provides large Purcell enhancement and simultaneously the photonic crystal guides almost all scattering light into its edge state, the rate of nonscattering single photons reaches more than 10^{4}γ_{0}. This topological state-led mode coupling mechanism and induced absorption reduction, which are based on topological protection, will have a profound effect on the study of composite topological photonic structures and related micro- and nanoscale cavity quantum electrodynamics. Also, nonscattering large Purcell enhancement will provide practical use for on-chip quantum light sources, such as single-photon sources and nanolasers.