The normal-auxeticity mechanical phase transition in graphene

Abstract

When a solid object is stretched, in general, it shrinks transversely. However, the abnormal ones are
\nauxetic, which exhibit lateral expansion, or negative Poisson ratio. While graphene is a paradigm
\n2D material, surprisingly, graphene converts from normal to auxetic at certain strains. Here, we
\nshow via molecular dynamics simulations that the normal-auxeticity mechanical phase transition
\nonly occurs in uniaxial tension along the armchair direction or the nearest neighbor direction. Such
\na characteristic persists at temperatures up to 2400 K. Besides monolayer, bilayer and multi-layer
\ngraphene also possess such a normal-auxeticity transition. This unique property could extend the
\napplications of graphene to new horizons.