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Negative Valley Polarization of the Intralayer Exciton via One-Step Growth of H-Type Heterobilayer WS2/MoS2

Authors
Le, Chinh TamLee, Je-HoKim, DonggyuJang, MyeongjinYoon, Jun-YeongKim, KwanpyoJang, Joon I.Seong, Maeng-JeKim, Yong Soo
Issue Date
Feb-2023
Publisher
American Chemical Society
Keywords
2D materials; H-type WS2/MoS2; intralayer excitons; valley switching; valleytronics
Citation
ACS Nano, v.17, no.3, pp 2629 - 2638
Pages
10
Journal Title
ACS Nano
Volume
17
Number
3
Start Page
2629
End Page
2638
URI
https://scholarworks.bwise.kr/cau/handle/2019.sw.cau/66321
DOI
10.1021/acsnano.2c10581
ISSN
1936-0851
1936-086X
Abstract
Vertical type II van der Waals heterobilayers of transition metal dichalcogenides (TMDs) have attracted wide attention due to their distinctive features mostly arising from the emergence of intriguing electronic structures that include moiré-related phenomena. Owing to strong spin-orbit coupling under a noncentrosymmetric environment, TMD heterobilayers host nonequivalent +K and -K valleys of contrasting Berry curvatures, which can be optically controlled by the helicity of optical excitation. The corresponding valley selection rules are well established by not only intralayer excitons but also interlayer excitons. Quite intriguingly, here, we experimentally demonstrate that unusual valley switching can be achieved using the lowest-lying intralayer excitons in H-type heterobilayer WS2/MoS2 prepared by one-step growth. This TMD combination provides an ideal case for interlayer coupling with an almost perfect lattice match, thereby also in the momentum space between +K and -K valleys in the H-type heterostructure. The underlying valley-switching mechanism can be understood by bright-to-dark conversion of initially created electrons in the valley of WS2, followed by interlayer charge transfer to the opposite valley in MoS2. Our suggested model is also confirmed by the absence of valley switching when the lowest-lying excitons in MoS2 are directly generated in the heterobilayer. In contrast to the H-type case, we show that no valley switching is observed from R-type heterobilayers prepared by the same method, where interlayer charge transfer does not occur between the opposite valleys. We compare the case with the series of valley polarization data from other heterobilayer combinations obtained under different excitation energies and temperatures. Our valley switching mechanism can be utilized for valley manipulation by controlling the excitation photon energy together with the photon helicity in valleytronic devices derived from H-type TMD heterobilayers. © 2023 American Chemical Society.
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