  Hard sphere colloidal particles are a basic model system for general research
into phase behavior, ordering and out-equilibrium glass transitions.
Experimentally it has been shown that oscillatory shearing of a monodisperse
hard sphere glass, produces two different crystal orientations; a Face Centered
Cubic (FCC) crystal with the close packed direction parallel to shear at high
strains and an FCC crystal with the close packed direction perpendicular to
shear at low strains. Here, using Brownian dynamics simulations of hard sphere
particles, we have examined high volume fraction shear-induced crystals under
oscillatory shear as well as the same volume fraction glass counterparts. We
find that, while the displacements under shear of the glass are isotropic, the
sheared FCC crystal structures oriented parallel to shear, are anisotropic due
to the cooperative motion of velocity-vorticity layers of particles sliding
over each other. These sliding layers generally result in lower stresses and
less overall particle displacements. Additionally, from the two crystal types,
the perpendicular crystal exhibits less stresses and displacements at smaller
strains, however at larger strains, the sliding layers of the parallel crystal
are found to be more efficient in minimizing stresses and displacements, while
the perpendicular crystal becomes unstable. The findings of this work suggest
that the process of shear-induced ordering for a colloidal glass is facilitated
by large out of cage displacements, which allow the system to explore the
energy landscape and find the minima in energy, stresses and displacements by
configuring particles into a crystal oriented parallel to shear.
