Local shear dominance in equation of state of metallic glass under hydrostatic pressure

Amorphous solids are generally believed to best obey the equation of state derived for homogeneous and isotropic solids under hydrostatic pressure. However, departure from some of the widely accepted theories is observed recently in metallic glasses and no mechanistic explanation is given. Here, we reveal that the underlying cause is the presence of the local internal shear induced by hydrostatic pressure. This subtle phenomenon is difficult to acquire experimentally and is generally ignored in formulating the equation of state. We show that the applied hydrostatic pressure can indeed induce and simultaneously couple to the internal local shear stress that leads to local shear deformation. The internal shear deformation results in a topological transition characterized by a gradual change of the nearest coordination numbers manifested in the deviation in the equation of state. We argue that the reported pressure-shear interaction is a general feature for the class of disordered materials.