Interlayer coupling effect in van der Waals heterostructures of transition metal dichalcogenides
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Front. Phys. 16(1), 13501 (2021)
Research article Interlayer coupling effect in van der Waals heterostructures of transition metal dichalcogenides Yuan-Yuan Wang, Feng-Ping Li, Wei Wei† , Bai-Biao Huang, Ying Dai‡ School of Physics, State Key Laboratory of Crystal Materials, Shandong University, Jinan 250100, China Corresponding authors. E-mail: † [email protected], ‡ [email protected] Received July 10, 2020; accepted August 24, 2020
Van der Waals (vdW) heterobilayers formed by two-dimensional (2D) transition metal dichalcogenides (TMDCs) created a promising platform for various electronic and optical properties. ab initio band results indicate that the band offset of type-II band alignment in TMDCs vdW heterobilayer could be tuned by introducing Janus WSSe monolayer, instead of an external electric field. On the basis of symmetry analysis, the allowed interlayer hopping channels of TMDCs vdW heterobilayer were determined, and a four-level k·p model was developed to obtain the interlayer hopping. Results indicate that the interlayer coupling strength could be tuned by interlayer electric polarization featured by various band offsets. Moreover, the difference in the formation mechanism of interlayer valley excitons in different TMDCs vdW heterobilayers with various interlayer hopping strength was also clarified. Keywords van der Waals heterostructures, transition metal dichalcogenides, interlayer coupling effects, k·p model, interlayer exciton
1 Introduction In recent years, two-dimensional (2D) transition metal dichalcogenides (TMDCs) have attracted enormous attention as promising candidates for photonics, optoelectronics, and valleytronics [1, 2]. In regard to 2D TMDCs, the optical properties are characterized by tightly bound excitons, assigned to which the large exciton binding energy. In the light of inversion symmetry breaking, monolayer TMDCs present coupled spin–valley properties, which can be addressed by circularly polarized light excited excitons [3, 4]. It is inevitable in 2D monolayers that, however, sizeable electron–hole wave function overlap results in short (intralayer) exciton lifetimes and exchange interactions causes short valley polarization lifetimes due to the rapid valley mixing, being the major obstacles for the application of monolayer TMDCs in optoelectronics and valleytronics [5–8]. It is conclusive that the spin and valley degrees of freedom of charge carriers are associated with magnetic moments, while the layer degree of freedom in layered structures is relate to electric polarization. Therefore, combining two monolayer TMDCs into van der Waals (vdW) bilayer structures provides an unprecedented opportunity to realize the strong coupling between spin, valley as well ∗ Special
Topic: Heterojunction and Its Applications (Ed. Chenghua Sun). arXiv: 2009.01394.
as the layer pseudospin [9, 10]. It should be pointed out that the electronegativity difference between atomic layers may introduce an interlayer potential energy gradient in the TMDCs heterobilayers, which can cause appropriate en
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