Glasses behave as solids on experimental time scales due to their slow relaxation. Growing dynamic length scales due to cooperative motion of particles are believed to be central to this slow response. For quiescent glasses, however, the size of the cooperatively rearranging regions has never been observed to exceed a few particle diameters, and the observation of long-range correlations has remained elusive. We have provided direct experimental evidence of long-range correlations during the deformation of a dense colloidal glass. 

 

 

When an external stress is imposed, colloidal glasses deform via plastic rearrangement of particles. The investigation of spatial correlations of local strain reveals that plastic rearrangements generate a long-range quadrupolar strain field, which is similar to strain field around an Eshelby's inclusion. When the applied shear exceeds a critical shear rate, it induces a transition from homogeneous to inhomogeneous flow. Our results demonstrate that long-range strain correlations play a central role in determining the macroscopic deformation of glasses.