Charged Bosons Made of Fermions in Bilayer Structures with Strong Metallic Screening
Zheng Sun, Jonathan Beaumariage, Qiaochu Wan, Hassan Alnatah, Nicholas Hougland, Jessica Chisholm, Qingrui Cao, Kenji Watanabe, Takashi Taniguchi, Benjamin Hunt, Igor V. Bondarev, David W. Snoke
Abstract
Two-dimensional monolayer structures of transition metal dichalogenides (TMDs) have been shown to allow many higher-order excitonic bound states, including trions (charged excitons), biexcitons (excitonic molecules), and charged biexcitons. We report here experimental evidence and the theoretical basis for a new bound excitonic complex, consisting two free carriers bound to an exciton in a bilayer structure. Our experimental measurements on structures made using two different materials show a new spectral line at the predicted energy with two different TMD materials (MoSe2 and WSe2) with both n- and p-doping if and only if all the required theoretical conditions for this complex are fulfilled, in particular, only in the presence of a parallel metal layer that significantly screens the repulsive interaction between the like-charge carriers. Because these four-carrier bound states are charged bosons, they could eventually be the basis for a new path to superconductivity without Cooper pairing.