  When exposed to strong shearing, the particles in a crystal will rearrange
and ultimately, the crystal will break by forming large nonaffine defects. Even
for the initial stage of this process, only little effort has been devoted to
the understanding of the breaking process on the scale of the individual
particle size for thermalized mixed crystals. Here, we explore the
shear-induced breaking for an equimolar two-dimensional binary model crystal
with a high interaction asymmetry between the two different species such that
the initial crystal has an intersecting square sublattice of the two
constituents. Using Brownian dynamics computer simulations, we show that the
combination of shear and thermal fluctuations leads to a characteristic
hierarchical breaking scenario where initially, the more strongly coupled
particles are thermally distorted, paving the way for the weakly coupled
particles to escape from their cage. This in turn leads to mobile defects which
may finally merge, proliferating a cascade of defects, which triggers the final
breakage of the crystal. This scenario is in marked contrast to the breakage of
one-component crystals close to melting. Moreover, we explore the orientational
dependence of the initial shear direction relative to the crystal orientation
and compare this to the usual melting scenario without shear. Our results are
verifiable in real-space experiments of superparamagnetic colloidal mixtures at
a pending air-water interface in an external magnetic field where the shear can
be induced by an external laser field.
