  The common notion suggests that metallic glasses (MGs) are a homogeneous
solid at the macroscopic scale; however, recent experiments and simulations
indicate that MGs contain nano-scale elastic heterogeneities. Despite the
fundamental importance of these findings, a quantitative understanding is still
lacking for the local elastic heterogeneities intrinsic to MGs. On the basis of
Eshelby's theory, here we develop a micromechanical model that correlates the
properties of the local elastic heterogeneities, being very difficult to
measure experimentally, to the measurable overall elastic properties of MGs,
such as shear/bulk modulus and Poisson's ratio. Our theoretical modeling is
verified by the experimental data obtained from various MGs annealed to
different degrees. Particularly, we revealed that the decrease of Poisson's
ratio upon annealing of MGs is associated with a much large shear softening
over hydrostatic-pressure softening, and $vice$ $versa$ in local elastic
inhomogeneities. The relative extent of the bulk versus shear modulus softens
is extracted for different MGs, and is found to closely depend on the specific
composition and their ductility. The implication of our results on the
Poisson's ratio criterion on the ductility as well as the aging dynamics in MGs
is discussed.
