Fig. 1: Layer index engineering of the internal structure of three-body trionic systems.
From: Correlated fermionic-bosonic insulating states in twisted hetero-trilayer semiconductors
a Internal structure of the trion evolves from an intra-layer to an inter-layer and then to a charge-layer-locked (CLL) geometry. b Symmetric type-II band alignments in the WSe2/WS2/WSe2 hetero-trilayer, with the outer two WSe2 layers arranged in an AB configuration. Solid and dashed orange arrows indicate spin-up and spin-down states, respectively. VB (CB) denotes the valence (conduction) band. c Charge distributions of the CLL trion and inter-layer excitons (IXs) in the trilayer and bilayer regions, respectively (top panel). IX-top denotes the inter-layer exciton in the top bilayer (WSe2/WS2); IX-bottom denotes the inter-layer exciton in the bottom bilayer (WS2/WSe2); CLL trion denotes the charge-layer-locked trion in the trilayer (WSe2/WS2/WSe2). The optical microscope image of a WSe2/WS2/WSe2 hetero-trilayer is displayed in the bottom panel (Sample 1), where the regions of top WSe2 monolayer (dashed blue line), middle WS2 monolayer (dashed red line) and bottom WSe2 monolayer (dashed yellow line) are marked. I, II, and III denote the bottom bilayer, top bilayer and trilayer regions, respectively. The top bilayer of this hetero-trilayer structure is in an R-type stacking while the bottom bilayer in an H-type stacking. Scale bar is 20 μm. d Photoluminescence (PL) spectra of the top bilayer (Top BL: WSe2/WS2), bottom bilayer (Bottom BL: WS2/WSe2) and trilayer (WSe2/WS2/WS2) regions measured at 10 K from Sample 1. The PL intensity of inter-layer excitons in the top bilayer is multiplied by a factor of 0.2 for clarity. Excitation power is 5.64 μW.
