It was generally assumed that dislocations could not exceed the speed of sound in shear-wave velocity because the energy expended in radiation exhibited a singularity at that point. Atomistic simulations showed here that dislocations could move faster than the speed of sound if they were created as supersonic dislocations at a high stress concentration and were subjected to high shear stresses. This behavior was obviously analogous to the concept of the tachyon in relativity theory, but might also have practical importance in understanding low-temperature deformation processes such as twinning.

Dislocations Faster than the Speed of Sound. P.Gumbsch, H.Gao: Science, 1999, 283[5404], 965-8