Definitive Evidence of Excitonic Charged Bosons in a bilayer system

Van der Waals (vdW) heterostructures have emerged as a promising platform for discovering novel excitonic bound states, including trions, biexcitons and charged biexciton complexes [1]. In previous experiments, we reported evidence for a new bound excitonic state in a bilayer transition metal dichalcogenide (TMD) structure: an intralayer trion bound to a like charge in an adjacent layer, forming a doubly charged "quaternion." This asymmetric state is stable due to metallic screening in the system in our specially designed structure, which mitigates the repulsion between like charges [2].

Our recent electrostatic measurements provide definitive confirmation of this charged boson complex. By continuously varying the doping density with both positive and negative carriers, we observed the expected dependence on free carrier density and asymmetry in the doping of two different layers, aligning with theoretical predictions.

These findings are significant because they suggest that the quaternion state could potentially undergo Bose-Einstein condensation (BEC), offering the possibility of a new type of superconductor with net charge. Our results open the door to further exploration of BEC and superconductivity in vdW heterostructures, positioning this system as a strong candidate for future research in quantum materials.