  We discuss a possible principle for detecting dark matter axions in galactic
halos. If axions constitute a condensate in the Milky Way, stimulated emissions
of the axions from a type of excitation in condensed matter can be detectable.
We provide general mechanism for the dark matter emission, and, as a concrete
example, an emission of dark matter axions from magnetic vortex strings in a
type II superconductor are investigated along with possible experimental
signatures.
