Excitonic Inherited Characteristics Of Polaritons And Polariton Devices In TMDs Microcavity

Presently atomically thin semiconducting materials known as transition metal dichalcogenides(TMDs)belonging to group-? have gained enormous interest from optoelectronics and physics researchers because of their outstanding and appealing properties.Among all of their distinctive properties,the most important are their direct band gaps,strong excitonic binding energies and stable cavity polaritons at room temperature.These unique properties pave a way for next generation optoelectronic devices,valleytronics,spintronics and excitons polaritons coupled applications.In 2D group-VI TMDs,electrons and holes are bound together with high binding energy ranging0.5-1 me V.These tightly bound excitons can be potentials candid for the strong light and matter coupling and providing a way to rise to the stable polaritons inside the microcavity at room temperature when they are coupled together with the photons.The polaritons are light matter quasi particles,which are lighter in mass and faster in speed(equal to speed of light).The polaritons are helpful to study the characteristics of excitons-polaritons inside the cavity.Exciton-polaritons offer an excellent platform for future photoelectronic devices and quantum information applications,and could be manipulated in multiple ways to design the optoelectronics devices based on light matter strong coupling.In this thesis,strong light-matter properties of 2D group-? TMDs have been investigated and have been manipulated in various ways to design and analyse the optoelectronics devices based on strongly coupled excitons and cavity photons,the so-called polaritons.First,we have investigated the formation of polaritons through strong coupling between WS₂ excitons and cavity photons,especially;the control of Optical Stark Effect(OSE)on polaritons is studied.A polarization dependent model is proposed to study the change of strongly coupled excitons and photons in WS₂ microcavity.It is exposed through both steady and dynamical states analysis that an outside optical Stark pulse can efficiently change the polariton characteristics such as dispersion,exciton and photon fractions through blue shifting of excitonic resonance.Therefore,the analysis and control of excitons-polaritons in a WS₂ microcavity by means of spin-selective optical pump could be achievable.Then,we analysed theoretically that valley-spin selective OSE could generate ultrafast and relative high valley pseudo-magnetic field in exciton-polariton regime.The novelty of this part is that our analysis revel the excitonic-inherent dispersion characteristic and OSE of polaritons in TMD microcavity.Based on the above model and analysis,our work proposed an approach to design polaritonic Multimode Interferometer in a WS₂ microcavity by an all-optical control method.The interference phenomenon of cavity polaritons is controlled by the OSE.The optical Stark beam changes dispersion(e.g.,effective refractive index)of the illuminated region,and makes a waveguide region therein.In this way,it is supporting various guided modes of polaritons.Multimode interference of polaritons is then guided by changing the beam pattern or intensity of the optical Stark light.This proposed method is then theoretically analysed and proved by way of effective refractive index calculation and eigenmode analysis of plane waveguide.This is the first idea of using OSE to form waveguide structure of polaritons,which provide an efficient way in control and manipulation of polaritons flows.Finally,we proposed a device,which takes advantage of the spin sensitive properties of OSE of polaritons inside the WS₂ microcavity,to guide different modes and modulate polarization of polaritons.It is shown that polaritonic wavepacket of different mode profiles can be generated by changing intensity of the optical Stark beam,and the polarization of polaritons can be modulated periodically along the formed waveguide by introducing birefringence that is sensitive to polarization degree of the optical Stark beam.This work extends our idea of OSE-induced polaritonic waveguide into polarization sensitive devices taking advantage of spin-valley sensitive characteristics of polaritons,providing additional degree of freedom for light and matter control.