Electrically controlled interlayer trion fluid in electron-hole bilayers.

The combination of repulsive and attractive Coulomb interactions in a quantum electron-hole (e-h) fluid can produce correlated phases of multiparticle charge complexes, such as excitons, trions, and biexcitons. We report an experimental realization of an electrically controlled interlayer trion fluid in van der Waals heterostructures. In strongly coupled e-h bilayers, electrons and holes spontaneously form three-particle trion bound states. The interlayer trions can assume 1e-2h and 2e-1h configurations. We show that the two holes in 1e-2h trions form a spin-singlet with a spin gap of approximately one milli–electron volt. By electrostatic gating, the equilibrium state can be continuously tuned into an exciton fluid, a trion fluid, an exciton-trion mixture, or a trion-charge mixture. Our work demonstrates a platform to study correlated phases of tunable Bose-Fermi mixtures. Editor's summary: Semiconductors can host multiparticle electron-hole states, which are usually short-lived due to electron-hole recombination. A promising system for studying their equilibrium properties are double layers of transition metal dichalcogenides, in which the carrier density in each layer can be independently controlled. Qi et al. and Nguyen et al. engineered an equilibrium quantum liquid of trions consisting of, for example, two holes and an electron in Coulomb-coupled molybdenum and tungsten diselenide (MoSe2/WSe2) double layers (see the Perspective by Ouyang and Shi). To achieve this, the researchers tuned the ratio of electron density in the MoSe2 layer to the hole density in the WSe2 layer and used transport, capacitance, and optical measurements to probe the system. —Jelena Stajic [ABSTRACT FROM AUTHOR]