Double Indirect Interlayer Exciton in a MoSe₂/WSe₂ van der Waals Heterostructure

Abstract

An emerging class of semiconductor heterostructures involves stacking discrete monolayers such as transition metal dichalcogenides (TMDs) to form van der Waals heterostructures. In these structures, it is possible to create interlayer excitons (ILEs), spatially indirect, bound electron-hole pairs with the electron in one TMD layer and the hole in an adjacent layer. We are able to clearly resolve two distinct emission peaks separated by 24 meV from an ILE in a MoSe/WSe heterostructure fabricated using state-of-the-art preparation techniques. These peaks have nearly equal intensity, indicating they are of common character, and have opposite circular polarizations when excited with circularly polarized light. Ab initio calculations successfully account for these observations: they show that both emission features originate from excitonic transitions that are indirect in momentum space and are split by spin-orbit coupling. Also, the electron is strongly hybridized between both the MoSe and WSe layers, with significant weight in both layers, contrary to the commonly assumed model. Thus, the transitions are not purely interlayer in character. This work represents a significant advance in our understanding of the static and dynamic properties of TMD heterostructures.

Exciton physics and device application of two-dimensional transition metal dichalcogenide semiconductors

“…Here, the strong Coulomb interaction gives rise to the formation of interlayer excitons, where the involved electrons and holes are located in different TMD layers ( Fig. 2b) [22,23,71,[86][87][88][89][90]. After optical excitation of regular intralayer excitons, holes or electrons can tunnel to the other layer forming interlayer excitons.…”

Indirect Excitons and Trions in MoSe2/WSe2 van der Waals Heterostructures

“…A splitting of IX or DX emission to two luminescence lines is a general phenomenon in two coupled TMD layers. Various interpretations based on the assignment of the lines to different states of neutral excitons were offered to explain this splitting: The interpretations in terms of (i) excitonic states split due to the CB K-valley spin splitting, 29 (ii) excitonic states indirect in momentum space and split due to the valley energy difference 32,38 or spin-orbit coupling, 39 and (iii) excitonic states in moiré superlattice [43][44][45][46][47][48] following the theory of moiré IXs and DXs. [50][51][52] However, interpretations based on different states of neutral excitons do not offer a good agreement with the experimental data in Fig.…”

Giant Valley-Zeeman Splitting from Spin-Singlet and Spin-Triplet Interlayer Excitons in WSe2/MoSe2 Heterostructure

“…This high valley polarization arises from the long valley lifetime of the hole [51][52][53] . The optically excited electron-hole pairs can quickly dissociate and separate into two layers [66][67][68][69] , but the intervalley scattering of the hole is strongly inhibited 34,50,51 , especially for resonance excitation [35][36][37][38][39][40] . This sensitive temperature dependence of the valley polarization for both interlayer exciton can be easily illustrated in Fig.…”