Study On Magnetoplasmons In Graphene

In order to meet the development of science and technology,the miniaturization and integration of photonic devices are extremely required.Controlling the light behavior in the nanoscale is one of the key factor.As a light wave form that bounded to the metal surface,surface plasmon polaritons(SPPs)provides with an efficient approach to modulate the light wave.SPPs are the collective oscillation of free electrons near the metal surface,which is featured as the high confinement of light.As a consequence,the property and geometric shape of the metal has a large influence on SPPs.In recent years,lots of literatures have reported that the strong light modulation is achieved by utilizing the geometric property of nano structures,for instance,optical sensing,nonlinear enhancement by localized field,photocatalysis,metasurface,etc.However,SPPs in metals are very hard to tune actively.Graphene that is the firstly fabricated two dimensional materials,has stable mechanical property,tunable Fermi energy level,large conductivity and so on,making itself the hot research topic in the area of fundamental research and application.Such active tenability can be easily achieved in graphene plasmon.One of the methods is electric gating,for example,the property of SPPs supported by graphene can be regulated through controlling the concentration of free carries with electrostatic field.It should be noted that the magneto-optical effects also can be applied to realize active tenability.Since graphene has very strong magneto-optical effects,and in presence of a magnetic field,the carrier will undergoes a cyclotron motion.The collective excitation in such system is usually called magnetoplasmons.However,the relevant research in this direction is far to be enough.On the basis of above mentioned background,this article investigated the magneto-plasmon on graphene nano structures with different geometric and edge shapes by using theoretic and simulation methods.The content and conclusion of the thesis is as follows:(1)We investigate the excitation of magnetoplasmons in graphene nanostructures with different shapes.We show that in the presence of a static magnetic field,plasmonic dipolar modes will split and the splitting is symmetrical in regular polygons.The splitting depends not on the size but only on the number of sides of the regular polygons.Larger splitting will occur in regular polygons with more sides,where the maximum splitting is achieved in circular disks.We further introduce a simple Lorentz model that could provide an excellent description of optical excitations in regular polygons.Finally,we examine the magnetoplasmons in the shapes without rotational symmetry,such as rectangles,where the symmetry of the splitting breaks as well.(2)For the combination of different shape of inner edges and outer edges,perforated graphene presents different magnetoplasmonic properties.The energy difference of magnetoplasmonic modes varies along with the graphene ring width,and the critical width in which the energy difference equals to zero related to the cyclotron radius and cyclotron resonance frequency.Only the width of the graphene ring is larger than the critical width,the symmetrical splitting can be observed under the external magnetic field.Moreover,the symmetrical splitting can be eliminated for the studied rings by increasing the long side of rectangle edge(including the inner and the outer edges).In this instance,only one mode dominates in the extinction spectrum.For the split graphene ring,only one dipolar magnetoplasmonic mode can be excited under the external magnetic field.