Discontinuous Evolution of the Structure of Stretching Polycrystalline Graphene.

Polycrystalline graphene has an inherent tendency to buckle, i.e. develop out-of-plane, three-dimensional structure, yielding a rich landscape of configurations. A force applied to stretch a piece of polycrystalline graphene influences the out-of-plane structure. In this talk, we show that if the graphene sheet is well-relaxed, as long as is not completely crystalline, this happens in non-linear fashion: occasionally, a tiny increase in stretching force induces a significant displacement, an avalanche-like event in which ridges and vertices are created and annihilated around the defects, which in turn can create vibrations in the surrounding medium [1]. We establish this effect in computer simulations: by continuously changing the strain, we follow the non-affine displacements of the atoms that turn out to exhibit a discontinuous evolution. Furthermore, the displacements exhibit a hysteretic behavior upon the change from low to high stress and back. Our results motivate further studies of dynamical elasticity of polycrystalline quasi-two-dimensional systems, and in particular the implications on their mechanical and thermal properties.

[1] F. D'Ambrosio, V. Juričić and G. T. Barkema, Phys. Rev. B 100, 161402 (2019).