Tuning exciton complexes in twisted bilayer WSe2 at intermediate misorientation

TL;DR

This study investigates how intermediate twist angles in bilayer WSe2 influence excitonic complexes, revealing unique phenomena like neutral biexciton formation and tunable excitonic behavior through electrostatic doping.

Contribution

It provides the first detailed analysis of excitonic complexes in intermediate misorientation twisted bilayer WSe2, highlighting their controllability and unique physical effects.

Findings

Neutral biexciton observed only in twisted bilayers

Charged biexcitons are stable against thermal dissociation

Doping controls excitonic complexes and suppresses indirect IL excitons

Abstract

Twist angle modifies the band alignment, screening, and interlayer (IL) coupling in twisted bilayers (tBLs) of transition metal dichalcogenides. Intermediate misorientation (twist angles > 15 degrees) bilayers (BLs) offer a unique opportunity to tune excitonic behavior within these concurrent physical mechanisms but are seldom studied. In this paper, we measure many-body excitonic complexes in monolayer (ML), natural BL, and tBL WSe2. Neutral biexciton (XX) is observed in tBL, while being undetected in nonencapsulated ML and BL, demonstrating unique effects of disorder screening in tBLs. The XX as well as charged biexciton are robust to thermal dissociation and are controllable by electrostatic doping. Vanishing of momentum-indirect IL excitons with increasing electron doping is demonstrated in tBL, resulting from the near alignment of Q-K and K-K valleys. Intermediate misorientation samples offer a high degree of control of excitonic complexes while offering possibilities for studying exciton-phonon coupling, band alignment, and screening.