  The relaxations of conductivity have been studied in a strongly disordered
two-dimensional (2D) electron system in Si after excitation far from
equilibrium by a rapid change of carrier density n_s at low temperatures T. The
dramatic and precise dependence of the relaxations on n_s and T strongly
suggests (a) the transition to a glassy phase as T->0, and (b) the Coulomb
interactions between 2D electrons play a dominant role in the observed
out-of-equilibrium dynamics.
