Interlayer Exciton in atomically reconstructed MoSe2/WSe2

H.J. Chuang
Naval Research Labortory,
United States

Keywords: Interlayer exciton, Moire, Reconstruction

Summary:

Van der Waals layered materials, such as transition metal dichalcogenides (TMDs), are an exciting class of layered materials with weak interlayer bonding which enables one to create so-called van der Waals heterostructures (vdWH). One promising attribute of vdWH is control over the twist angle between layers, which leads to the formation of Interlayer exciton (ILE) when forming a type II band alignment heterostructure, WSe2/MoSe2 heterostructure in this study. With hBN encapsulation and a relative rotational angle close to 60 degrees, well pronounced ILE emission is observed at room temperature and further splits into two distinct peaks (ILE1 and ILE2) at low temperature. Furthermore, we demonstrate that the ILE emission peaks have opposite circular polarizations when excited by circularly polarized light. Ab initio calculations provide an explanation of this unique and potentially useful property and indicate that it is a result of the indirect character of both transitions. We further investigate the atomic structure arrangement of MoSe2/WSe2 by TEM and reveal that the heterostructure reconstructs under a small twist angle between the TMDs. While a rigid moiré structure is observed by TEM when a larger twist angle (≥ 3°) is applied, with a small twist angle (≤1°), periodic domains form with commensurate stacking within each domain. This finding provides evidence that a significant departure from current rigid-lattice moiré theory, which only considers the constituent layers as rigid lattices and does not allow for atomic-level reconstruction, is needed to describe small twist angle systems. These results may also provide fundamental insights into the mechanical and optical behavior of this exciting class of semiconductor heterostructure