3 years ago

Stress-controlled Poisson ratio of a crystalline membrane: Application to graphene.

I.S. Burmistrov, M.I. Katsnelson, A. D. Mirlin, I.V. Gornyi V.Yu. Kachorovskii, J.H. Los

We demonstrate that a key elastic parameter of a suspended crystalline membrane---the Poisson ratio (PR) $\nu$---is a non-trivial function of the applied stress $\sigma$ and of the system size $L$, i.e., $\nu=\nu_L(\sigma)$. We consider a generic 2D membrane embedded into space of dimensionality $2+d_c$. (The physical situation corresponds to $d_c=1$.) A particularly important application of our results is free-standing graphene. We find that at very low stress, where the membrane exhibits a linear response, the PR $\nu_L(0)$ decreases with increasing system size $L$ and saturates for $L\to \infty$ at a value which depends on the boundary conditions and is essentially different from the value $\nu=-1/3$ previously predicted by the membrane theory within a self-consisted scaling analysis. By increasing $\sigma$, one drives a membrane into a non-linear regime characterized by a universal value of PR that depends solely on $d_c.$ This universal non-linear PR acquires its minimum value $\nu_{\rm min}=-1$ in the limit $d_c\to \infty.$ With the further increase of $\sigma$, the PR changes sign and finally saturates at a positive non-universal value prescribed by the conventional elasticity theory. We also show that one should distinguish between the absolute and differential PR ($\nu$ and $\nu^{\rm diff}$, respectively). While coinciding in the limits of very low and very high stresses, they differ in general, $\nu \neq \nu^{\rm diff}$. In particular, in the non-linear universal regime, $\nu^{\rm diff}$ takes a universal value which, similarly to absolute PR, is a function solely of $d_c$ but is different from the universal value of $\nu$. In the limit $d_c\to \infty$, the universal value of $\nu^{\rm diff}$ tends to $-1/3$, at variance with the limiting value $-1$ of $\nu$. Finally, we briefly discuss generalization of these results to a disordered membrane.

Publisher URL: http://arxiv.org/abs/1801.05476

DOI: arXiv:1801.05476v1

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