  During devitrification, pre-existing crystallites grow by adding particles to
their surface via a process that is either thermally activated (diffusive mode)
or happens without kinetic barriers (fast crystal growth mode). It is yet
unclear what factors determine the crystal growth mode and how to predict it.
With simulations of repulsive hard-sphere-like (Weeks-Chandler-Andersen)
glasses, we show for the first time that the same system at the same volume
fraction and temperature can devitrify via both modes depending on the
preparation protocol of the glass. We prepare two types of glass, a
conventional glass (CG) via fast quenching and a uniform glass (UG) via density
homogenization. Firstly, we bring either glass into contact with a crystal (X)
and find the inherent structure (CGX/UGX). During energy minimization, the
crystal front grows deep into the CG interface, while the growth is minimal for
UG. When thermal noise is added, this behavior is reflected in different
crystallization dynamics. CGX exhibits a density drop at the crystal growth
front which correlates with enhanced dynamics at the interface and a fast
growth mode. This mechanism may explain the faster crystal growth observed
below the glass transition experimentally. In contrast, UGX grows via
intermittent avalanche-like dynamics localized at the interface, a combination
of localized mechanical defects and the exceptional mechanical stability
imposed by the UG glass phase.
