A perfect crystal is pushed past its elastic limit. Dislocations nucleate massively. What follows is unexpected: the crystal's mechanical response becomes statistically indistinguishable from a glass.
Salman, Ahadi, and Truskinovsky show that after elastic instability triggers extensive dislocation nucleation, dislocation avalanches follow power-law statistics with exponents that match those of amorphous materials — both before and after yielding. The system drives itself to marginal stability, the same state that glasses reach through quenching from a liquid.
The crystal structure doesn't change. Atoms remain on lattice sites. But the collective mechanical behavior — the statistics of how the material deforms — loses all memory of crystalline order. Perfect periodicity at the atomic scale coexists with perfect disorder in the response statistics.
This is “self-induced marginality.” The system doesn't need external tuning to reach criticality. The deformation process itself is the tuning mechanism. Push a crystal hard enough, and it tunes itself to the edge without any external parameter adjustment.
The implication is that the distinction between crystalline and glassy isn't structural but statistical. Two materials can have completely different atomic arrangements yet identical mechanical response statistics. Conversely, the same atomic arrangement (FCC crystal) can produce either crystalline or glassy response statistics depending on its deformation history. The material remembers what happened to it, not what it's made of.