Direct experimental measurement of the speed-stress relation for   dislocations in a plasma crystal
  The speed-stress relation for gliding edge dislocations was experimentally measured for the first time. The experimental system used, a two-dimensional plasma crystal, allowed observation of individual dislocations at the "atomistic" level and in real time. At low applied stress dislocations moved subsonically, at higher stress their speed abruptly increased to 1.9 times the speed of shear waves, then slowly grew with stress. There is evidence that immediately after nucleation dislocations can move faster than pressure waves. 
V. Nosenko, G. E. Morfill, P. Rosakis
cond-mat.soft