Citation: 
QingHai Tan, Xin Zhang, XiangDong Luo, Jun Zhang, PingHeng Tan. Layernumber dependent highfrequency vibration modes in fewlayer transition metal dichalcogenides induced by interlayer couplings[J]. Journal of Semiconductors, 2017, 38(3): 031006. doi: 10.1088/16744926/38/3/031006
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Q H Tan, X Zhang, X D Luo, J Zhang, P H Tan. Layernumber dependent highfrequency vibration modes in fewlayer transition metal dichalcogenides induced by interlayer couplings[J]. J. Semicond., 2017, 38(3): 031006. doi: 10.1088/16744926/38/3/031006.

Layernumber dependent highfrequency vibration modes in fewlayer transition metal dichalcogenides induced by interlayer couplings
doi: 10.1088/16744926/38/3/031006
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Abstract
Twodimensional transition metal dichalcogenides (TMDs) have attracted extensive attention due to their many novel properties. The atoms within each layer in twodimensional TMDs are joined together by covalent bonds, while van der Waals interactions combine the layers together. This makes its lattice dynamics layernumber dependent. The evolutions of ultralow frequency (<50 cm^{1}) modes, such as shear and layerbreathing modes have been wellestablished. Here, we review the layernumber dependent highfrequency (>50 cm^{1}) vibration modes in fewlayer TMDs and demonstrate how the interlayer coupling leads to the splitting of highfrequency vibration modes, known as Davydov splitting. Such Davydov splitting can be well described by a van der Waals model, which directly links the splitting with the interlayer coupling. Our review expands the understanding on the effect of interlayer coupling on the highfrequency vibration modes in TMDs and other twodimensional materials. 
References
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