Moiré excitons in twisted TMD heterostructures. (a) and (b) Optical microscopy image (a) and side-view illustration (b) of a representative heterostructure with a near-zero twist angle. (c) A zoomed-in image of atomic-resolution STEM of near-zero twist angle WSe₂/WS₂ bilayers showing the moiré superlattice. The two superlattice vectors are labelled. (d) Reflection contrast spectrum of near-zero twist angle WSe₂/WS₂ bilayers (top) compared to a large twist angle one (bottom). (e) Reflection contrast spectra in the range between 1.6 eV and 1.8 eV of the WSe₂. A exciton upon electron doping. The electron concentration is noted for each spectrum in units of cm⁻². Reprinted with permission from Ref. [8]. Copyright 2019, Nature Publishing Group.