Stacking atomically thin films enables artificial construction of van der Waals heterostructures with exotic functionalities such as superconductivity,the quantum Hall effect,and engineered light-matter interactions.In particular,heterobilayers composed of monolayer transition metal dichalcogenides have attracted significant interest due to their controllable interlayer coupling and trapped valley excitons in moiré superlattices.However,the identification of twist-angle-modulated optical transitions in heterobilayers is sometimes controversial since both momentum-direct(K-K)and-indirect excitons reside on the low energy side of the bright exciton in the monolayer constituents.Here,we attribute the optical transition at～1.35 eV in the WS2/WSe2 heterobilayer to an indirect Γ-K transition based on a systematic analysis and comparison of experimental photoluminescence spectra with theoretical calculations.The exciton wavefunction obtained by the state-of-the-art GW-Bethe-Salpeter equation approach indicates that both the electron and hole of the excitons are contributed by the WS2 layer.Polarization-resolved k-space imaging further confirms that the transition dipole moment of this optical transition is dominantly in-plane and is independent of the twist angle.The calculated absorption spectrum predicts that the so-called interlayer exciton peak coming from the K-K transition is located at 1.06 eV,but with a much weaker amplitude.Our work provides new insight into the steady-state and dynamic properties of twist-angle-dependent excitons in van der Waals heterostructures.

Ke Wu;Hongxia Zhong;Quanbing Guo;Jibo Tang;Jing Zhang;Lihua Qian;Zhifeng Shi;Chendong Zhang;Shengjun Yuan;Shunping Zhang;Hongxing Xu

School of Physics and Technology and Key Laboratory of Artificial Micro-and Nano-Structures of Ministry of Education,Wuhan University,Wuhan 430072,China;School of Physics,Huazhong University of Science and Technology,Wuhan 430074,China;The Institute for Advanced Studies,Wuhan University,Wuhan 430072,China;Key Laboratory of Materials Physics of Ministry of Education,School of Physics and Microelectronics,Zhengzhou University,Zhengzhou 450052,China

国家科学评论（英文版）

[1]Ke Wu;Hongxia Zhong;Quanbing Guo;Jibo Tang;Jing Zhang;Lihua Qian;Zhifeng Shi;Chendong Zhang;Shengjun Yuan;Shunping Zhang;Hongxing Xu-.Identification of twist-angle-dependent excitons in WS2/WSe2 heterobilayers)[J].国家科学评论（英文版）,2022(06):51-58

heterobilayers,heterobilayer,Salpeter

Identification,twist,angle,excitons,WS2,WSe2,Stacking,atomically,thin,films,enables,artificial,construction,van,der,Waals,heterostructures,exotic,functionalities,such,superconductivity,quantum,Hall,effect,engineered,light,matter,interactions,In,particular,composed,monolayer,metal,dichalcogenides,have,attracted,significant,interest,due,their,controllable,interlayer,coupling,trapped,valley,moir,superlattices,However,identification,modulated,optical,transitions,sometimes,controversial,since,both,momentum,indirect,reside,low,energy,bright,constituents,Here,attribute,eV,systematic,analysis,comparison,experimental,photoluminescence,spectra,theoretical,calculations,wavefunction,obtained,by,state,GW,Bethe,equation,approach,indicates,that,electron,hole,are,contributed,Polarization,resolved,space,imaging,further,confirms,dipole,this,dominantly,plane,independent,calculated,absorption,spectrum,predicts,called,peak,coming,from,located,much,weaker,amplitude,Our,work,provides,new,insight,into,steady,dynamic,properties

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