Investigation on the Fano-Type Asymmetry in Atomic Semiconductor Coupled to the Plasmonic Lattice

The investigation on the coherent coupling in the plasmon-TMDCs hybrid system is attracting great attention for its high tunability of the systematic components as well as for the potential applications on the nanophotonic devices. Abundant investigations of the plasmon-exciton hybrid system focused on the internal Rabi-type coupling from week coupling regime to strong coupling regime. Here, we demonstrate the Fano-type asymmetry in the open plasmon-exciton system both theoretically and experimentally. The theoretical framework based on the cavity electrodynamics (CQED) is first proposed to distinguish the Fano-type asymmetry from Rabi-type asymmetry. The former is due to the interference process, while the latter is due to the detuning of the plasmonic and excitonic resonances. The Fano-type interference process is found to enhance the lower energy branch (LEB) and reduce the higher energy branch (HEB), resulting in the Fano-type asymmetry in the output spectra, even at zero detuning. The theoretical predictions are confirmed through the layer-dependent and temperature-dependent measurements on the mono- and multilayer WSe2-plasmonic lattice system. We found that distinct from the Rabi-type process, where the internal plasmon-exciton coupling dominates, the Fano-type process is also highly dependent on the external excitations on the exciton and plasmon components. Our work sheds light on the Fano interference process in the plasmon-exciton coupled system and would boost the applications of novel two-dimensional plasmonic polaritonic devices in the field of ultrasensing or detection.