  Resonant optical excitation was used to create a macroscopic non-equilibrium
ensemble of dark excitons with unprecedentedly long lifetime in a
two-dimensional (2D) electron system placed in a quantizing magnetic field.
Exotic three-particle and four-particle states, plasmarons and plasmon-exciton
molecules, coupled with the surrounding electrons through the collective plasma
oscillations are engineered. Plasmarons and plasmon-exciton molecules are
manifested as new features in the recombination spectra of non-equilibrium
systems. Magnetoplasmarons and magnetotrions in a two-dimensional Hall
insulator.
