Fig. 1

Photoluminescence spectroscopy of bilayer WSe₂. a Optical micrograph of a WSe₂ flake exfoliated onto Si/SiO₂ with monolayer (ML) and bilayer (BL) regions indicated by the arrows (scale bar, 15 μm). b Cryogenic raster-scan photoluminescence map of the upper corner indicated by the dashed square in a. False-color plot of the photoluminescence maxima in the spectral range of 1.43–1.59 eV. The bilayer exhibits extended and punctual regions of brightening attributed to strain at local folds. c Normalized photoluminescence spectrum (brown, magnified by a factor of 20 in the range of 1.62–1.82 eV) at a representative bilayer position away from defects with model fit shown as red solid line. The energy positions of momentum-bright (X and D) and momentum-dark BL excitons (Q_↑Γ, Q_↑K, K_↓Γ, \(K'_ \uparrow K\), K_↑Γ, and \(K'_ \downarrow K\), labeled by the capital letters of electron and empty state valleys and the electron out-of-plane spin as subscript) are indicated by dashed lines. All spectroscopy measurements were performed at 4.2 K with excitation at 1.95 eV