Department of Physics, The Chinese University of Hong Kong, Hong Kong, China.
Chem Soc Rev. 2015 May 7;44(9):2629-42. doi: 10.1039/c4cs00265b. Epub 2015 Apr 21.
The ultimate goal of making atomically thin electronic devices stimulates intensive research on layered materials, in particular the group-VI transition metal dichalcogenides (TMDs). Atomically thin group-VI TMD crystals with a 2H stacking order emerging as a family of intrinsic 2-dimensional (2D) semiconductors with a sizeable bandgap in the visible and near infrared range satisfy numerous requirements for ultimate electronics and optoelectronics. In addition, the characteristic inversion symmetry breaking presented in monolayer TMDs leads to non-zero but contrasting Berry curvatures and orbit magnetic moments at K/K' valleys located at the corners of the first Brillouin zone. These features provide an opportunity to manipulate electrons' additional internal degrees of freedom, namely the valley degree of freedom, making monolayer TMDs a promising candidate for the conceptual valleytronics. Besides, the strong spin-orbit interactions and the subsequent spin-valley coupling demonstrated in atomically thin group-VI TMDs open up potential routes towards quantum manipulation. In this tutorial review, we highlight recent advances in the optical study on electronic structures, vibrational properties, excitonic effects, valley dependent optical selection rules, and the interplay of valley, spin, and layer degrees of freedoms in this class of atomic 2D semiconductors including MoS2, MoSe2, WS2, and WSe2.
将原子层薄的电子器件付诸实践这一终极目标激发了人们对层状材料，尤其是 VI 族过渡金属二卤化物（TMDs）的深入研究。具有 2H 堆叠顺序的原子层薄 VI 族 TMD 晶体是一类本征二维（2D）半导体，在可见光和近红外范围内具有相当大的带隙，满足了终极电子学和光电子学的诸多要求。此外，在单层 TMDs 中表现出的特征反转对称性破缺导致在第一布里渊区角处的 K/K' 谷中出现非零但相反的 Berry 曲率和轨道磁矩。这些特性为操纵电子的附加内部自由度（即谷自由度）提供了机会，使单层 TMDs 成为概念 valleytronics 的有前途的候选者。此外，在原子层薄的 VI 族 TMDs 中表现出的强自旋轨道相互作用和随后的自旋谷耦合为量子操纵开辟了潜在途径。在本教程综述中，我们强调了在电子结构、振动特性、激子效应、谷依赖光选择定则以及谷、自旋和层自由度相互作用的光学研究方面的最新进展，包括 MoS2、MoSe2、WS2 和 WSe2 等这类原子二维半导体。
