Strongly correlated excitons in atomic double layers

Excitonic insulators (EIs) occur in a small-gap semiconductor when the electron-hole binding energy exceeds the charge bandgap. They can also occur in small band overlap semimetals. The ground state exciton population is determined by balancing the negative exciton formation energy against the mean exciton-exciton repulsion energy. EIs provide a solid-state platform for quantum many-boson physics. Although the concept has been understood for decades, establishing distinct experimental signatures of the realization of EIs has remained challenging. In this talk, I discuss a recent experiment in which we establish electrical control of the chemical potential of interlayer excitons in atomic double layers of semiconducting transition metal dichalcogenide and probe the thermodynamic properties of exciton fluids by capacitance measurements. I will also discuss the possibility of creating exciton fluids in a lattice to realize the Bose-Hubbard model.