  Active systems are inherently out of equilibrium, as they collect energy from
their surroundings and transform it into directed motion. A recent theoretical
study suggests that binary mixtures of active particles with distinct effective
diffusion coefficients exhibit dynamical demixing above a threshold ratio of
the diffusion coefficients. Here, we show that this threshold may be reduced
drastically in the presence of external fields. We investigate the demixing as
a function of the ratio of the diffusion coefficients and discuss the
implications of the results for active systems.
