Band Properties Of Hexagonal Lattice Modulated By External Field

Hexagonal lattice materials have been extensively studied for their special structures,of which graphene is representative.However,since graphene has a zero band gap,it is difficult to apply it to a semiconductor device.Graphene nanoribbons precisely solve this problem,and their bandgap sizes vary depending on the different type of boundary.Its special nature has attracted researchers' curiosity and great interest in it.In this thesis,we start with the introduction of the structure properties of graphene and the band structure of graphene nanoribbons.Then we introduce the corresponding theoretical models and research methods.Finally,we use the above methods to systemat-ically investigate the band structure and transport properties of graphene nanoribbons.Firstly,we modulate the energy band structure of graphene nanoribbons by chang-ing a single external field,thereby changing their transport properties.It is found that the energy gap of the graphene nanoribbon increases linearly with the increase of the AB sub-lattice potential.For different types of graphene nanoribbons,the variation of energy gap is also different under a non-uniform electric field.The band gaps of armchair graphene nanoribbons will vary with the uniaxial strain,but the band gaps of the zigzag graphene nanoribbons have almost no change.Secondly,we study the energy band of armchair graphene nanoribbons under both uniaxial strain and electric field,and find that the energy gap can be closed and opened.It is worth mentioning that the nanoribbons have boundary states and interface states under a perpendicular magnetic field,which is similar to that of topological insulator and topo-logical semimetal.Finally,we study the band structure and transport properties of the armchair graphene nanoribbons under both uniaxial strain and nonuniform electric field,we can realize the band gap also can be opened and closed.And an interesting quantized evolution behaviour of two-terminal conductance is obtained by applying a perpendicular magnetic field.Finally,we study the band structure and transport properties of the armchair graphene nanoribbons under both uniaxial strain and non-uniform electric field.It is found that the opening and closing of the energy gap can be achieved by regulating both potentials.The two-terminal conductance shows an interesting quantized evolution behavior by applying a perpendicular magnetic field.In summary,we have mainly explored the changes of band structure and transport properties of graphene nanoribbons under uniaxial strain,non-uniform electric field,non-uniform electric potential,sublattice potential and magnetic field.We hope that the results of this theoretical study can play a certain role in the future semiconductor electronics.