Two-Dimensional Valley Electrons and Excitons in Noncentrosymmetric 3R-MoS2
Two-Dimensional Valley Electrons and Excitons in Noncentrosymmetric 3R-MoS2
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DOI：
10.1103/physrevapplied.4.014002
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发表时间：
2015-07-10
影响因子：
4.6
通讯作者：
Arita, Ryotaro
中科院分区：
文献类型：
--
作者：
Akashi, Ryosuke;Ochi, Masayuki;Arita, Ryotaro
我们发现，当MoS_2层形成3R堆积时，谷电子--布里渊区K点和K‘点附近的电子态--的运动被限制在二维内，而在2H多型中，能带在所有三个维度上都有色散。根据我们的第一性原理能带结构计算，3R-MoS2中的谷态没有层间跳跃，这是Bloch函数旋转对称性的结果。通过测量反射率光谱和分析一个各向异性的氢原子模型，我们证实了3R-MoS_2中的谷激子具有二维类氢谱序列，并且波函数的扩散小于层间距。相反，2H-MoS_2中的谷激子被三维模型很好地描述，因此不局限于单层。我们的结果表明，谷面自由度的大小可以简单地通过堆积几何来控制，这可以在未来的电子技术中得到应用。
We find that the motion of the valley electrons-electronic states close to the K and K' points of the Brillouin zone-is confined into two dimensions when the layers of MoS2 form the 3R stacking, while in the 2H polytype, the bands have dispersion in all three dimensions. According to our first-principles band-structure calculations, the valley states have no interlayer hopping in 3R-MoS2, which is proven to be the consequence of the rotational symmetry of the Bloch functions. By measuring the reflectivity spectra and analyzing an anisotropic hydrogen-atom model, we confirm that the valley excitons in 3R-MoS2 have two-dimensional hydrogenlike spectral series, and the spreads of the wave function are smaller than the interlayer distance. In contrast, the valley excitons in 2H-MoS2 are well described by the three-dimensional model and, thus, not confined in a single layer. Our results indicate that the dimensionality of the valley degree of freedom can be controlled simply by the stacking geometry, which can be utilized in future valleytronics.