Study And Real-time Tuning Of Strong Coupling Interaction Between Plasmonic Nanocavity And Tungsten Disulfide

Study of strong coupling interaction between surface plasmons and excition has important application prospect in nanoscale nonlinear optics,quantum information calculation,polarization laser and other fields.Metal nanocavity and transition metal disulfide produced strong coupling phenomenon was studied by transmission,reflection and dark field scattering spectra.In recent years,the strong coupling characteristics based on nanocavity have been characterized mainly by dark field scattering spectroscopy.However,this method is difficult to accurately distinguish the strong coupling from the weak coupling such as enhanced absorption or Fano resonance.Photoluminescence spectra can directly reveal the level splitting under strong coupling,so the mode splitting of fluorescence spectra is a strong evidence to accurately judge the strong coupling.In this paper,dark field scattering and photoluminescence are used to study the coupling and tuning between excitons and plasma excitons.Firstly,we demonstrate a continuously tuning of strong coupling in the Ag/WS₂nanocavity by doping the photoluminescent material Spiropyran.Secondly,the coupling strength of the composite cavity was adjusted by changing the size of the silver cube particles.It was confirmed by both scattering and fluorescence spectra.Finally,the strong coupling strength between excitons and plasmon was improved by changing the dielectric environment around the plasma composite nanocavity.This conclusion has been proved experimentally by fluorescence spectrum.The main contents of this paper are as follows:(1)We designed an isopexciton composite nanocavity formed by the combination of monolayer WS₂and NPo M structure.We detected the Rabi splitting by a self-constructed dark field scattering light path and a laser confocal microscopy test system.Unlike scattering,PL does not display Fano interference.Splitting in the PL spectrum occurs only in the strong-coupling regime,and has therefore been recognized as the definitive signature of Rabi splitting.This tuning process was characterized by dark field scattering and fluorescence detection.(2)The dielectric layer of the composite structure is doped with photosensitive material SPI.By modulating the refractive index of dielectric layer with ultraviolet light and changing the resonant peak of plasmon,the Rabi splitting can be adjusted.We can accurately measure the coupling strength of composite cavities of different sizes under zero detuning condition,and obtain the dispersion diagram of the composite structure from a single particle.(3)We experimentally adjust the number of excitons involved in the coupling by changing the size of the silver cube particles in the plasma composite nanocavity.Then the coupling strength of the composite structure can be controlled in real time.The coupling strength can be improved from 65 me V to 170 me V by changing the silver cube particle size.At the same time,fluorescence can only detect Rabi splitting in the strong coupling region.When the size is less than 74 nm,the system is not in the strong coupling interval,the fluorescence spectrum does not appear splitting,and the double peak structure measured by dark field scattering is not Rabi splitting.(4)Tuning the electronegativity value of dielectric environment around the system,the density of neutral exciton in monolayer WS₂can be changed.Therefore,the WS₂-Ag nanocavity is immersed in the solution of ethanol or DCM.The accuracy of this experiment was confirmed by the use of fluorescence characterization.In the aethnol environment,the strong coupling strength increased from 140 me V to 180 me V,and the DCM solution increased the strong coupling strength to 270 me V.