Tuning exciton complexes in twisted bilayer WSe2 at intermediate misorientation

Twist angle modifies the band alignment, screening and interlayer coupling in twisted bilayers of transition metal dichalcogenides. Intermediate misorientation (twist angles θ > 15 ◦ ) bilayers offer a unique opportunity to tune excitonic behaviour within these concurrent physical mechanisms but are seldom studied. In this work, we measure many-body excitonic complexes in monolayer (ML), natural bilayer (BL) and twisted bilayer (tBL) WSe 2 . Neutral biexciton (XX) is observed in tBL for the first time, while being undetected in non-encapsulated ML and BL, demonstrating unique effects of disorder screening in twisted bilayers. The XX as well as charged biexciton (XX − ), are robust to thermal dissociation, and are controllable by electrostatic doping. Vanishing of momentum indirect interlayer excitons with increasing electron doping is demonstrated in tBL, resulting from near-alignment of Q − K and K − K valleys. Intermediate misorientation samples offer a high degree of control of excitonic complexes, while offering possibilities of studying exciton-phonon coupling, band-alignment, and screening.

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