Nature of Moiré Excitons in Rotationally Aligned and Misaligned MoSe2/WS2 Heterobilayers

APS  ·  2024

Mit Naik; Woochang Kim; Steven Louie;

HIGHLIGHT

Our parameter-free calculations reproduce the splitting of excitonic peaks observed in reflection contrast spectroscopy, and we find excitonic states with diverse spatial characteristics.

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ABSTRACT

Recent reflection contrast measurements on rotationally aligned and misaligned MoSe 2/WS 2 show the MoSe 2 ’A’ exciton peak split into two peaks for large twist-angles, and three to four peaks for small twist-angles. The current understanding suggests that the splitting of the peaks occurs as a result of hybridization of the electronic bands at the K-point conduction band minima of the two layers. Using first principles GW-Bethe Salpeter equation (GW-BSE) calculations, we investigate the origin and nature of the moiré exciton peaks. Our parameter-free calculations reproduce the splitting of excitonic peaks observed in reflection contrast spectroscopy, and we find excitonic states with diverse spatial characteristics. In contrast to the prevailing understanding, we find limited interlayer hybridization between the K-point states, with the exciton splitting in rotationally aligned MoSe 2/WS 2 primarily driven by structural reconstructions. The large-scale GW-BSE calculations in these moiré superlattice with ~4000 atoms in the moiré unit-cell is facilitated by the newly developed pristine unit-cell matrix projection (PUMP) approach 1. [1] M. H. Naik, E. C. Regan, Z. Zhang, …, F. H. Jornada, F. Wang, S. G. Louie, Nature 609, 52–57 (2022)

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