  It is well known that jammed soft materials will flow if sheared above their
yield stress - think mayonnaise spread on bread - but a complete microscopic
description of this seemingly sim- ple process has yet to emerge. What remains
elusive is a microscopic framework that explains the macroscopic flow, derived
from a 3-D spatially resolved analysis of the dynamics of the droplets or
particles that compose the soft material. By combining confocal-rheology
experiments on compressed emulsions and numerical simulations, we unravel that
the primary microscopic mechanisms for flow are strongly influenced by the rate
of the imposed deformation. When shearing fast, small coordinated clusters of
droplets move collectively as in a conga line, while at low rates the flow
emerges from bursts of droplet rearrangements, correlated over large domains.
These regions exhibit complex spatio-temporal correlation patterns that reflect
the long range elasticity embedded in the jammed material. These results
identify the three-dimensional structure of microscopic rearrangements within
sheared soft solids, revealing that the characteristic shape and dynamics of
these structures are strongly determined by the rate of the external shear.
