石墨烯超快动态光学性质  

Ultrafast dynamic optical properties of graphene

作　　者：金芹 董海明[1] 韩奎[1] 王雪峰[2] 

机构地区：[1]中国矿业大学理学院物理系,徐州221116 [2]苏州大学物理科学与技术学院,苏州215006

出　　处：《物理学报》2015年第23期317-323,共7页Acta Physica Sinica

基　　金：中央高校基本科研业务费专项基金(批准号:2013QNA29);国家自然科学基金(批准号:11247002)资助的课题~~

摘　　要：通过建立石墨烯的光学布洛赫方程,研究了弱光场下的单层石墨烯超快动态光学性质.理论研究表明在太赫兹辐射光场下由于泡利不相容和能量守恒原理使得石墨烯系统建立动态非平衡载流子并达到饱和的时间是20—200fs,能够在1ps之内迅速产生光电流.研究发现2^(1/2)ev_FE_0t?ω是石墨烯线性光学响应区;否则是石墨烯系统非线性光学响应区,E_0和ω分别对应入射光的强度和频率,t为时间,v_F是石墨烯狄拉克点附近电子的费米速度.研究发现光子能量ω越大,电极化强度以及光电流越强.我们的理论研究结果与已有的众多实验结果一致,表明石墨烯在超快动态光学领域尤其是太赫兹领域拥有重要的研究和应用价值.Graphene exhibits excellent ultrafast optical properties due to its unique electronic structure.In this paper we investigate theoretically the ultrafast dynamic optical properties of graphene based on the Bloch-equations,and introduce the theoretical model of graphene.First,we give the energy which has a linear relationship with the wave vector k.The behavior of electrons in the vicinity of the two Dirac points can be described by the massless Dirac-equation,thus we have the Dirac equation of graphene.Second,we discuss the interaction between graphene and light field.The Bloch-equations of graphene are obtained through the Heisenberg equation and then we discuss the photon carriers,electric polarization and optical current change over time by analyzing the Bloch-equations.It is found that the nonequilibrium carriers in graphene induced by a terahertz field can be built in 20–200 fs due to the Pauli blocking and the conservation of energy principle.The photon carrier density will increase with the frequency of enhanced light field.Thus an optical current can be created rapidly within 1 ps.A graphene system responds linearly to the external optical field for 21/2evFE0t？ω,while the graphene systems respond nonlinearly to the external optical field,where E0 and ω are respectively the intensity and the frequency of the light,t is the time and vF the Dirac velocity in graphene.The electric polarization and optical current increase with increasing photon energies.These theoretical results are in agreement with recent experimental findings and indicate that graphene exhibits important features and has practical applications in the ultrafast optic filed,especially in terahertz field.

关 键 词：石墨烯 超快动态 光学性质 布洛赫方程 

分 类 号：O613.71[理学—无机化学]