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arXiv 1302.5218cond-mat.mes-hall
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扭曲双层石墨烯的光吸收

Optical Absorption in Twisted Bilayer Graphene

Pilkyung Moon, Mikito Koshino

摘要:

我们从理论上研究了具有不同堆叠几何形状的扭曲双层石墨烯的光吸收特性,并证明了光谱特性可以作为指纹来识别两层之间的旋转角度。我们发现,吸收光谱几乎连续演变的旋转角度的变化,无论晶格的可折叠性。该谱的特征在于与van Hove奇异性相关的一系列峰,并且峰能量随旋转角系统地移动。我们在紧束缚模型和基于狄拉克方程的有效连续模型两种不同的框架下计算了光吸收。对于小于$10^\circ$的小旋转角,有效模型很好地再现了紧束缚模型的低能能带结构和光学电导率,并且还根据有效哈密顿量的对称性解析地解释了光学选择规则。

英文摘要:

We theoretically study the optical absorption property of twisted bilayer graphenes with various stacking geometries, and demonstrate that the spectroscopic characteristics serve as a fingerprint to identify the rotation angle between two layers. We find that the absorption spectrum almost continuously evolves in changing the rotation angle, regardless of the lattice commensurability. The spectrum is characterized by series of peaks associated with the van Hove singularity, and the peak energies systematically shift with the rotation angle. We calculate the optical absorption in two different frameworks; the tight-binding model and the effective continuum model based on the Dirac equation. For small rotation angles less than $10^\circ$, the effective model well reproduces the low-energy band structure and the optical conductivity of the tight-binding model, and also explains the optical selection rule analytically in terms of the symmetry of the effective Hamiltonian.

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