Figure 1: Effect of stress level on dislocation loop expansion at 20 K from MD simulations.

(a) The loop developed into a track-field-like geometry when the external applied shear stress was fixed at 1.5 GPa, consistent with the traditional understanding that screw dislocations move much slower than edge dislocations. (b) When the externally applied shear stress was increased to 4 GPa, the dislocation loop kept a roughly round shape during its expanding process. This means that the mobility of the screw and edge segments now becomes similar under such high stresses.