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Discovery of intralayer charge transfer moiré excitons

We studied the excitonic spectrum of a rotationally aligned WS2/WSe2 moiré superlattice using parameter-free first principles GW-BSE calculations. These calculations unveiled a remarkably diverse array of moiré excitons, surpassing the predictive capacity of prevailing continuum models. We uncovered a unique category of intralayer charge-transfer excitons. While charge-transfer excitons are commonly found in molecular solids or at material interfaces due to a type-II band alignment, this study marked the first observation of charge-transfer exciton within a single layer of a two-dimensional material. Experimental investigations into the behavior of intralayer moiré excitons under the influence of charge doping and magnetic fields, as observed through reflection contrast spectroscopy, provided empirical support for these theoretical predictions. This pioneering work was published in Nature, contributing significantly to our understanding of moiré exciton states in transition metal dichalcogenide heterostructures. The calculations on the moiré unit-cell housing ~2000 atoms was made possible by developing a novel computational method, called pristine unit-cell matrix projection (PUMP) approach.

Nature 609, 52–57 (2022).

Nature Materials (accepted).

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