State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences , P.O. Box 912, Beijing 100083, China.
College of Materials Science and Engineering, Jilin University , Changchun 130012, China.
ACS Nano. 2016 Jan 26;10(1):1619-24. doi: 10.1021/acsnano.5b07273. Epub 2016 Jan 13.
In two-dimensional transition-metal dichalcogenides, both spin-orbit coupling and interlayer coupling play critical roles in the electronic band structure and are desirable for the potential applications in spin electronics. Here, we demonstrate the pressure characteristics of the exciton absorption peaks (so-called excitons A, B and C) in monolayer, bilayer, and trilayer molybdenum disulfide (MoS2) by studying the reflectance spectra under hydrostatic pressure and performing the electronic band structure calculations based on density functional theory to account for the experimental observations. We find that the valence band maximum splitting at the K point in monolayer MoS2, induced by spin-orbit coupling, remains almost unchanged with increasing pressure applied up to 3.98 GPa, indicating that the spin-orbit coupling is insensitive to the pressure. For bilayer and trilayer MoS2, however, the splitting shows an increase with increasing pressure due to the pressure-induced strengthening of the interlayer coupling. The experimental results are in good agreement with the theoretical calculations. Moreover, the exciton C is identified to be the interband transition related to the van Hove singularity located at a special point which is approximately 1/4 of the total length of Γ-K away from the Γ point in the Brillouin zone.
在二维过渡金属二硫属化物中，自旋轨道耦合和层间耦合在电子能带结构中都起着关键作用，对于自旋电子学的潜在应用是可取的。在这里，我们通过研究静压下的反射光谱并基于密度泛函理论进行能带结构计算来解释实验观察结果，展示了单层、双层和三层二硫化钼（MoS2）中激子吸收峰（所谓的激子 A、B 和 C）的压力特性。我们发现，单层 MoS2 中由自旋轨道耦合引起的 K 点价带顶分裂在高达 3.98 GPa 的压力下几乎保持不变，表明自旋轨道耦合对压力不敏感。然而，对于双层和三层 MoS2，由于层间耦合的压力诱导增强，分裂随压力的增加而增加。实验结果与理论计算吻合较好。此外，激子 C 被确定为与位于布里渊区 Γ-K 方向上约 1/4 总长度处的特殊点的范霍夫奇点相关的带间跃迁。
