Optical response of graphene under intense terahertz fields
Optical response of graphene under intense terahertz fields
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DOI：
10.1103/physrevb.83.245436
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发表时间：
2011-06-28
影响因子：
3.7
通讯作者：
Wu, M. W.
中科院分区：
文献类型：
--
作者：
Zhou, Y.;Wu, M. W.
基于Floquet理论研究了石墨烯在强圆偏振和线偏振太赫兹场存在下的光学响应。我们检查能级谱和态密度。发现由于单光子和多光子共振，准能谱中出现了间隙。准能隙在小动量时较为明显，但随着动量的增大而急剧减小，当动量足够大时，准能隙趋于闭合。由于大动量状态的贡献，与Oka和Aoki [Phys]先前工作的预测相反，状态密度的差距被有效地关闭了。Rev. B 79, 081406(R)(2009)]。我们还研究了不同场强和费米能量下石墨烯的光学导电性，并展示了石墨烯中动态Franz-Keldysh效应的主要特征。研究发现，由于边带调制的光学跃迁，光学电导率呈多阶梯状结构。还表明，在低费米能量的情况下，由于小动量下的准能隙，在应用太赫兹场频率的整数频率上出现了下降。此外，在圆极化太赫兹场下，我们预测了“阶跃”中间的峰值和由光学电导率中零动量周围状态的贡献引起的峰值。
Optical responses of graphene in the presence of intense circularly and linearly polarized terahertz fields are investigated based on the Floquet theory. We examine the energy spectrum and density of states. It is found that gaps open in the quasienergy spectrum due to the single-photon and multiphoton resonances. These quasienergy gaps are pronounced at small momentum, but decrease dramatically with the increase of momentum, and finally tend to be closed when the momentum is large enough. Due to the contribution from the states at large momentum, the gaps in the density of states are effectively closed, in contrast to the prediction in the previous work by Oka and Aoki [Phys. Rev. B 79, 081406(R) (2009)]. We also investigate the optical conductivity for different field strengths and Fermi energies, and show the main features of the dynamical Franz-Keldysh effect in graphene. It is discovered that the optical conductivity exhibits a multi-steplike structure due to the sideband-modulated optical transition. It is also shown that dips appear at frequencies being the integer numbers of the applied terahertz field frequency in the case of low Fermi energy, originating from the quasienergy gaps at small momentums. Moreover, under a circularly polarized terahertz field, we predict peaks in the middle of the "steps" and peaks induced by the contribution from the states around zero momentum in the optical conductivity.