Fig. 1.

Multi-particle bound states in 1L-WSe_2. a Conduction and valence band configurations at the K and K’ valleys. The color for the bands reflects the spin of the electron states. b The schematics of valley-spin configurations of bound states. We use blue (red) to denote spin up (down) and closed (open) symbols to represent K (K’) valley. Illustrated are the bright exciton (X), the dark exciton (D) and the negatively charged trions (T₁/T₂). Only states with holes in the K valley upper valence band are shown here. c A typical luminescence spectrum of high-quality 1L-WSe₂ excited by 2.33 eV laser at 4 K. Inset: The OM image of the sandwiched hBN/1L-WSe₂/hBN heterostructure. The scale bar is 10 μm. d The power-dependent intensity of X, XD, and TD emissions. The dashed (dot) lines in the figure are drawn for $P\propto I$ $\left(P\propto I^2\right)$