Plasmons And Some Related Elementary Excitations In Semimetallic 2D Materials

With the development of optoelectronic devices based on two-dimensional materials,people have witnessed a growing academic interest in plasmon in semimetallic 2D materials.In this thesis,we theoretically derives the analytical expression of polarization function in graphene and 8-Pmmn borophene by the way of Lehmann representation of polarization function under the random phase approximation.The plasmon dispersion in semimetallic 2D materials is given by making the dielectric function zero.In longwavelength limit,The plasmon dispersion in graphene is no longer the classical dispersion as ω_q～q^1/2,but the linear dispersion.The 8-Pmmn borophene has an anisotropy and tilted Dirac cone which is different from graphene.This results the plasmon modes possess kinks at the boundary of the interband single particle continuum,and the obvious anisotropic behavior.In the short-wavelength limit,all the plasmon modes approach to the same dispersion at a suffciently large interlayer spacing.This thesis is mainly divided into the following parts to explain the research content:Chapter 1 introduces the development of common semimetallic 2D materials,the theory and experiment of plasmon and current status in this field,and the significance of this thesis.Chapter 2 introduces the derivation of dielectric function based on random phase approximation and linear response theory.Meanwhile,this chapter also established the basic theory of plasmon on conventional metals.Chapter 3 derives the polarization function in graphene,receives the analytical expression of the polarization function and gives the plasmon dispersion according to the zero point of the dielectric function.We also consider the plasmon-phonon coupling in graphene.The ω-q relation is received by derving the polarization function at the long-wavelength limit and the plasmon-phonon coupled mode dispersion diagram is plotted under different layers of graphene.Chapter 4 derives the polarization function in 8-Pmmn borophene.As a result,we receive the analytical expression of the polarization function and the plasmon dispersion.In addition,we also study the plasmon dispersion in multilayer 8-Pmmn borophene and explains the influence of anisotropic and tilted Dirac cone to plasmon.Chapter 5 gives a summary and looks forward to the future work and development prospects in the plasmon field.In this thesis,we study the plasmon in semimetallic 2D materials,receive the dispersion of plasmon and plasmon-phonon coupled mode according to the analytical derivation of polarization function and establish a solid theoretical foundation for the development of optoelectronic devices.