Structural change, plasticity and avalanches in cyclically sheared silica*

Strong glasses are often characterized by strong directional interactions and  present a completely different behaviour with respect to their fragile counterpart. Under cyclical deformation they are known to display a sharply defined yielding transition with a discontinuous jump from an absorbing to a diffusive state similar to fragile glasses. In this work, we show that silica as a prototypical strong glass former under athermal quasi static cyclic deformation exhibits nontrivial plastic rearrangements. In contrast to mean-field predictions, the statistics of avalanches reveals significant qualitative change in their scaling behaviour. Across the yielding transition system exhibits a qualitative structural change which can be attributed to the crucial role of 5-fold coordination defects of silicon atoms. Such defects facilitate the strain localization in a densified shear-banded region above the yield strain.