Effect of heavy impurities on the plasticity of amorphous solids

We investigate the effect of heavy impurities on the mechanical properties and plasticity of a modeled amorphous solid by introducing a small fraction of these impurities into the material which resembles real experimental systems. The impurities being mobile, the total degrees of freedom and the potential energy landscape of the pure system are preserved in our model. The mechanical failure and the shear band formation in the amorphous solid in the presence of impurities are studied at the microscopic level by employing the finite shear deformation protocol at nonzero temperature. A significant enhancement in the yield stress is observed as a function of the heaviness of the impurity particles. Via the analysis of the nonaffine displacement field and the microscopic strain fluctuations and the nature of their spatial correlations we find that the shear band formation in the plastic regime is gradually suppressed with increasing impurity mass. Eventually, a crossover mass of the impurity particles is identified above which the plastic events become completely localized. This is marked by a transition from a power law to an exponential decay in the spatial correlations nonaffine displacement field. Likewise, a similar change is observed in the strain correlation function, transitioning from a slower 1/r decay to a more rapid 1/r^{3} decay. Finally, the effect shear rate on the plastic events in the presence of impurities is explored.