  A fascinating feature of metallic glasses is their ability to explore
different configurations under mechanical deformations. This effect is usually
observed through macroscopic observables, while little is known on the
consequence of the deformation at atomic level. Using the new generation of
synchrotrons, we probe the atomic motion and structure in a metallic glass
under hydrostatic compression, from the onset of the perturbation up to a
severely-compressed state. While the structure indicates reversible
densification under compression, the dynamic is dramatically accelerated and
exhibits a hysteresis with two regimes. At low pressures, the atomic motion is
heterogeneous with avalanche-like rearrangements suggesting rejuvenation, while
under further compression, aging leads to a super-diffusive dynamics triggered
by internal stresses inherent to the glass. These results highlight the
complexity of the atomic motion in non-ergodic systems and support a theory
recently developed to describe the surprising rejuvenation and strain hardening
of metallic glasses under compression.
