Observation of a Topological Transition Point During Dynamic Failure of Brittle Solids

We observed a topologic phase transition in the course of dynamic failure of brittle films of several minerals under indentation loads. Spatiotemporal distribution of the stress field was monitored with a nano-second resolution using multi-array piezo-electric transducers. From this data , we construct a dynamic acoustic crystal and observe a topological transition point in the acoustic band structure where the band inverts. We recognized three main features in the transition from pre-failure to post-failure regimes: existence of a solitonic state where multiple solitons –some of them with supersonic velocity- nucleate, propagate and collide; onset of nucleation of solitons- moving domain walls between distinct topological mechanical phases- is manifested in Van Hove singularities and the kinetic energy of the acoustic crystal shows an inverse symmetric form. We show that the inversion of symmetry occurs due to interactions of two types of solitons having opposite group velocities; one raises the energy while the other one lowers the kinetic energy of the acoustic crystal. The annihilation points of these two types of solitons are neutral points (i.e., Dirac-points of the crystal).