Double Indirect Interlayer Exciton in a MoSe2/WSe2 van der Waals Heterostructure (1802.05310v1)

Abstract: An emerging class of semiconductor heterostructures involves stacking discrete monolayers such as the 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 MoSe2/WSe2 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, are split by spin-orbit coupling, and that including interlayer hybridization is essential in correctly describing the ILE transition. Although well separated in momentum space, we find that in real space the electron has significant weight in both the MoSe2 and WSe2 layers, contrary to the commonly assumed model. This is a significant consideration for understanding the static and dynamic properties of TMD heterostructures.

Analysis of Double Indirect Interlayer Exciton in MoSe$_2$/WSe$_2$ Heterostructures

The research paper "Double Indirect Interlayer Exciton in a MoSe$_2$/WSe$_2$ van der Waals Heterostructure" by Hanbicki et al. focuses on the development of van der Waals heterostructures formed by the stacking of transition metal dichalcogenides (TMDs). Specifically, it investigates the properties of interlayer excitons (ILEs) in the MoSe$_2$/WSe$_2$ heterostructure. These excitons are spatially indirect, forming bound electron-hole pairs where the electron resides in one monolayer while the hole is in the adjacent layer.

Key Findings

The authors present experimental evidence delineating emission characteristics of ILEs in MoSe$_2$/WSe$_2$. Two distinct emission peaks were resolved, separated by 24 meV, with nearly equal intensity but opposite circular polarizations—a finding contrary to existing models. Notably, this behavior varies non-monotonically with excitation energy, enabled through advanced material preparation techniques and ab initio calculations. These peaks are attributed to excitonic transitions that are indirect in momentum space, signifying spin-orbit coupling alongside notable interlayer hybridization. Previous models, which suggested electrons reside largely within the Mo-layer, are contested by findings indicating significant electron presence in both layers. This insight challenges and refines the understanding of static and dynamic properties of TMD heterostructures.

Implications and Applications

The implications of these discoveries are multifaceted:

1. Theoretical Implications: The nature of interlayer hybridization mandates revisiting the assumed exciton dynamics in TMD heterostructures. By illustrating that hybridized electron eigenstates are superpositions of spin states, the paper suggests recalibrating theoretical models that dictate electronic transition mechanisms in semiconductor physics.
2. Practical Applications: Given the strong polarization attributes and interlayer hybridization of ILEs, MoSe$_2$/WSe$_2$ heterostructures become promising candidates for applications in valleytronic devices—a field progressively seeking materials with robust valley polarization characteristics.

Future Directions

The findings encourage further exploration into the manipulation and control of exciton properties through phonon and defect engineering within heterostructures. Such endeavors may unveil novel electronic behaviors and enhance optoelectronic device performance. The explicit control of excitonics and spin polarization opens avenues for advanced application in quantum computing and beyond.

Conclusion

This paper provides significant contributions to the understanding of interlayer excitons in TMD heterostructures, particularly addressing how such excitonic transitions are influenced by spin-orbit effects and interlayer hybridization. Through precise experimentation and calculated modeling, the research enriches the comprehension of electronic interactions in layered materials, prompting both theoretical and practical innovations within semiconductor technology. Further work is necessitated to exploit these findings in real-world applications, aligning with evolutions in nanotechnology and materials science.