Impacts of moiré potential on interlayer exciton transports in van der Waals heterostructures

Chien-Ju Lee^1*, Yan-Qi Huang¹, Fu-Hsien Chu¹, Bo-Han Lin¹, Li-Syuan Lu², Wen-Hao Chang^1,2

¹Department of Electrophysics, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
²Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan

* Presenter:Chien-Ju Lee, email:chienju1016@gmail.com

Recently, design and fabrication of van der Waals heterostructures have emerged as a new approach for engineering exciton properties in the two-dimensional limit. Heterobilayers (HBLs) of transition metal dichalcogenides (TMDs) generally possess a type-II band alignment, which facilitates the formation of spatially indirect interlayer excitons (IXs). Due to the separation of electrons and holes in different constituent monolayers, such IXs can interact with each other through repulsive Coulomb interactions among the aligned dipoles. Combined with their long radiative lifetime, IXs in TMD heterostructures hold great promises in realizing exciton based devices, which can efficiently connect optical communication and electrical processing systems. However, periodic potentials introduced by the moiré superlattice in stacked HBLs of TMDs can modulate the transport properties of IXs. Here we study the IX dynamics and transports in MoS₂/MoSe₂ HBLs under the influence of moiré potential using time-resolved photoluminescence imaging. Instead of pure diffusion like excitons in monolayer TMDs, the Coulomb repulsion of the aligned dipoles causes an exciton density-dependent drift of IXs immediately after the optical excitation. The moiré potential further imposes a twist angle-dependent spatial modulation of the IX transport. We have fabricated a series of HBLs with small twist angles by just one transfer process. Through excitation power, temperature, twist angle dependent measurements, we found that the transport property of IXs is affected by the interplay between moiré potentials and dipole-dipole interactions. Our results provide insights on understanding the transports of IXs in the moiré superlattice and facilitate the development of future optoelectronic applications.

Keywords: 2D materials, van der Waals heterostructure, exciton transport, moiré potentials