金属基外延石墨烯相图非谐效应探讨

Discussion on theanharmonic effect of phase diagram of metal-based epitaxial graphene

考虑到原子的非简谐振动,建立了物理模型,应用固体物理理论和方法,研究了金属基外延石墨烯电子系统的可能状态和相图,并以钨基底上的外延石墨烯为例,探讨了原子非谐振动和电子排斥作用对相图的影响。结果表明,(1)金属基外延石墨烯电子系统有3种可能相:自旋波状态(BC)的反铁磁相、电荷密度态(BZ)的顺磁相和半金属态(PM)的半金属相;(2)外延石墨烯呈现的相,取决于石墨烯中原子内部电子关联U和原子间电子关联G的变化。对钨基外延石墨烯而言,当U=0.33284 eV和G=0.11904 eV时,会出现半金属相、反铁磁相、顺磁相三相共存;(3)原子的非简谐振动对金属基外延石墨烯的相图有重要的影响。不考虑原子非简谐振动时,外延石墨烯的相变曲线与温度无关;而考虑原子非简谐振动后,相变曲线不仅与温度有关,而且对发生相变的条件要求更高:原子内部电子关联U要更强。温度愈高,发生半金属-反铁磁-顺磁相变愈难,原子非简谐振动效应愈显著。

In this paper,considering the atomic anharmonic vibration,a physical model was established.The solid state physics theory and method were applied to study the possible states and phase diagrams of the metal-based epitaxial graphene electronic system.Taking the epitaxial graphene on the tungsten substrate as an example,the effects of atomic non-resonant motion and electron repulsion on the phase diagram were discussed.The results show that the metal-based epitaxial graphene electronic system had three possible phases:the antiferromagnetic phase of the spin wave state(BC),the paramagnetic phase of the charge density state(BZ),and the semimetal phase of the semimetal state(PM).Secondly,the phase exhibited by the epitaxial graphene depended on the change of the internal electron association U of the atom in the graphene and the electron correlation G between the atoms.For tungsten-based epitaxial graphene,when U=0.33284 eVand G=0.11904 eV,it would exhibit the three-phase coexistence of semi-metal phase,antiferromagnetic phase and paramagnetic phase.Thirdly,the anharmonic vibration of an atom had an important influence on the phase diagram of metal-based epitaxial graphene.If the atomic non-harmonic vibration was not considered,the phase transition curve of the epitaxial graphene was independent of temperature,while considering the atomic anharmonic vibration,the phase transition curve was not only related to temperature,but also required higher conditions for the phase transition,that was the stronger atomic internal electron correlation U.The higher the temperature,the more difficult the semi-metal-antiferromagnetic-paramagnetic phase transition occurred,and the atomic anharmonic vibration effect was more pronounced.