  Electric deflections of niobium clusters in molecular beams show that they
have permanent electric dipole moments at cryogenic temperatures but not higher
temperatures, indicating that they are ferroelectric. Detailed analysis shows
that the deflections cannot be explained in terms of a rotating classical
dipole, as claimed by Anderson et al. The shapes of the deflected beam profiles
and their field and temperature dependences indicates that the clusters can
exist in two states, one with a dipole and the other without. Cluster with
dipoles occupy lower energy states. Excitations from the lower states to the
higher states can be induced by low fluence laser excitation. This causes the
dipole to vanish.
