Study On The Properties Of Plasmons Of Black Phosphorus And Graphene

Surface plasmons(SPs)generally refer to the special electromagnetic waves that propagate along the surface of metal and dielectric.Surface plasmons have unique physical properties,such as breaking the diffraction limit of photonic devices and enhancing the interaction between light and matter.In the early research on surface plasmons,noble metal was mainly used as the main materials,but the inherent loss of traditional noble metal was large,and its loss was difficult to tune,which caused great inconvenience to the application of plasmons.In addition,the working frequency band of plasmons generated in metal was mainly concentrated in the spectrum range from visible light to near infrared,and the working frequency band was very limited.Therefore,it is necessary to search for other materials that can support surface plasmons.Compared to traditional noble metals such as gold and silver,surface plasmons excited by two-dimensional materials such as graphene and black phosphorus(BP)support even stronger field localization;Secondly,it has the characteristics of low loss.Two-dimensional materials have extremely higher carrier mobility,lower loss and longer propagation life;Finally,dynamic tunability,the chemical potential of twodimensional materials can be modulated by applying voltage and doping,changing the band gap,changing the position of Fermi energy level,and thus changing the resonance frequency.Therefore,compared to noble metals,two-dimensional materials have better photoelectric tunability.In this thesis,we mainly study the influence of structural symmetry and material anisotropy on the excitation of plasmons through two-dimensional materials graphene and black phosphorus.We use COMSOL MULTIPHYSICS to carry out full wave simulations,and then use empirical formula to understand physical mechanism.The conclusions are as follows:(1)In ribbon,graphene and BP in armchair(AC)and zigzag(ZZ)directions show very similar plasmonic behavior,which can be well described by an empirical formula with the effective wavelength given by the width of ribbon.The difference between them exist mostly at the wavelength,since they have different Drude weight.(2)The effects of structural symmetry and material anisotropy on plasmon excitation are studied.In square,BP in ZZ direction shows a similar spectrum as graphene,namely,an extinction peak caused by dipole resonance;but BP in AC direction is completely different,two comparable peaks arising with none of them being dipole mode.The similar effect can also be designed in isotropic graphene,by means of breaking structural symmetry.(3)Studying the evolution of plasmonic resonances in BP rectangles,where both material anisotropy and structural symmetry are involved.As BP in AC direction,the extinction can be dominated by dipole resonance,if AC direction is the longer side,namely,the competing between structural symmetry and material anisotropy.(4)The plasmonic coupling effect in these two direction are also investigated through square rings.As reducing thickness of ring width,the dipole resonance of BP in ZZ direction shows a similar redshift as that of graphene ring.However,those of BP in AC direction are strongly modified,e.g.two modes following different behavior of variation.Our work reveals the influence of structural symmetry and material anisotropy on two-dimensional material plasmon resonance,which may promote the understanding of two-dimensional plasmon resonance.This thesis also investigates the generation of dual bound states in the continuum(BICs).By breaking the symmetry in both directions,we propose a dielectric metasurface that supports symmetry-protected BICs at terahertz(THz)frequency,achieving dual BICs and providing an alternative path for the implementation of dual BICs.The article has 25 pictures and 140 references.