  Many seemingly intractable systems can be reduced to a system of interacting
spins. Here, we introduce a system of artificial acoustic spins which are
manipulated with ultrasound excitations associated with micro-cracking sources
in thin sheets of crystals. Our spin-like system shows a peculiar relaxation
mechanism after inducing an impulsive stress-ramp akin to splitting, or
rupturing, of the system. Using real-time construction of correlations between
spins states, we observe a clear emergence of the light cone effect. It has
been proposed that equilibration horizon occurs on a local scale in systems
where correlations between distant sites are established at a finite speed. The
observed equilibration horizon in our observations defines a region where
elements of the material are in elastic communication through excited
elementary excitations. These results yield important insights into dynamic
communication between failing elements in brittle materials during processes
such as brittle fragmentation and dynamic stress triggering of
earthquake-generating faults.
