  A crystal of pure nickel grows from its melt at a rate that reaches 70 meters
per second. This extraordinary growth rate has led to the suggestion that
metallic crystals might provide the next generation of phase change materials.
The huge crystal growth rates of metals are a consequence of kinetics without
activated control, in sharp contrast to the prediction of the classic theory of
crystal growth. While the existence of growth kinetics without barriers is now
well established in atomic melts, no physical explanation for the absence of an
activation barrier to ordering has been established. It is something of a
paradox that diffusion in the liquid metal is governed by thermal activation
while the movement of the same atoms as they organize into a crystal is not. In
this paper we use computer simulations of crystallization in pure metals to
explicitly resolve the origin of the growth kinetics without barriers.
