Crossover from random three-dimensional avalanches to correlated nano shear bands in metallic glasses.

When applying mechanical stress to a bulk metallic glass it responds with elastic and/or plastic deformations. A comprehensive microscopic theory for the plasticity of amorphous solids remains an open task. Shear transformation zones consisting of dozens of atoms have been identified as smallest units of deformation. The connexion between local formation of shear transformations zones and the creation of macroscopic shear bands can be made using statistical analysis of stress/energy drops or strain slips during mechanical loading. Numerical work has proposed a power law dependence of those energy drops. Here we present an approach to circumvent the experimental resolution problem using a waiting time analysis. We report on the power law-distributed deformation behaviour and the observation of a crossover in the waiting times statistics. This crossover indicates a transition in the plastic deformation behaviour from three-dimensional random activity to a two-dimensional nano shear band sliding.