摘要:
考虑到原子的非简谐振动和电子-声子相互作用,建立了金属基外延石墨烯的物理模型,用固体物理理论和方法,得到金属基外延石墨烯的电导率和费米速度随温度变化的解析式.以碱金属基底为例,探讨了基底材料和非简谐振动对外延石墨烯电导率和费米速度的影响.结果表明:1)零温情况下,碱金属基外延石墨烯的电导率和费米速度均随基底元素原子序数的增大而增大;2)外延石墨烯的电导率随温度升高而减小,其中,温度较低时时变化较快,而温度较高时则变化很慢,费米速度随温度升高而增大,其变化率随基底材料原子序数的增大而增大;3)原子非简谐振动对外延石墨烯的电导率和费米速度有重要的影响,简谐近似下,费米速度为常数,电导率的温度变化率较大;考虑到原子非简谐项后,费米速度随温度升高而增大,电导率的温度变化率减小;温度愈高,原子振动的非简谐效应愈明显.
Abstract:
The atomic anharmonic vibration and the electron-phonon interaction are considered,and then a physical model about the metal-based epitaxial graphene is built.Variations of the electrical conductivity and the Fermi velocity with temperature for the metal-based epitaxial graphene are given based on the solid state physics theory or method.The alkali-metal epitaxial graphene is selected as the substrate,and then the influences of substrate material,electronphonon interaction and the anharmonic vibration on the electrical conductivity and the Fermi velocity of epitaxial graphene are discussed.Some results are shown as follows.Firstly,at zero temperature,the electrical conductivity and the Fermi velocity of the alkali-metal-base epitaxial graphene increase with the number of the atoms in substrate material increasing.Secondly,the electrical conductivity of epitaxial graphene decreases with temperature rising.Furthermore,the variation rate also decreases with temperature rising.Generally,the electrical conductivity originates mainly from electrons and phones.The electronic contribution to the electrical conductivity varies with temperature slowly,but the phone contribution to electrical conductivity varies with temperature evidently.Therefore,the contribution of phonons to electrical conductivity is much larger than that of electrons.Furthermore,the contribution increases with the number of atoms in basal elements.The phonon contribution to conductivity decreases with temperature rising,but it is unrelated to the basal elements.Thirdly,the Fermi velocity of the epitaxial graphene increases with temperature slowly.The variation of the Fermi velocity with temperature decreases with the increase of interaction between the graphene and the basal atoms.However,it increases with the number of atoms of the basal materials.The anharmonic effect causes important influences on the electrical conductivity and the Fermi velocity.Under the harmonic approximation the velocity is constant.However,the conductance increases rapidly with temperature.With considering the atomic anharmonic terms,the Fermi velocity increases with temperature.The variation of the electrical conductivity with temperature increasing becomes slower.If the temperature is higher,the anharmonic effects become more evident.
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