title: Auxetic Black Phosphorus: A 2D Material with Negative Poisson's Ratio.
abstract: The Poisson's ratio of a material characterizes its response to uniaxial strain. Materials normally possess a positive Poisson's ratio - they contract laterally when stretched, and expand laterally when compressed. A negative Poisson's ratio is theoretically permissible but has not, with few exceptions of man-made bulk structures, been experimentally observed in any natural materials. Here, we show that the negative Poisson's ratio exists in the low-dimensional natural material black phosphorus and that our experimental observations are consistent with first-principles simulations. Through applying uniaxial strain along armchair direction, we have succeeded in demonstrating a cross-plane interlayer negative Poisson's ratio on black phosphorus for the first time. Meanwhile, our results support the existence of a cross-plane intralayer negative Poisson's ratio in the constituent phosphorene layers under uniaxial deformation along the zigzag axis, which is in line with a previous theoretical prediction. The phenomenon originates from the puckered structure of its in-plane lattice, together with coupled hinge-like bonding configurations.
authors.affiliation: School of Electrical and Computer Engineering, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Yuchen
authors.initials: Y
authors.lastname: Du
authors.affiliation: School of Electrical and Computer Engineering, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.|Department of Physics and Atmospheric Science, Dalhousie University , Halifax, Nova Scotia B3H 4R2, Canada.
authors.forename: Jesse
authors.initials: J
authors.lastname: Maassen
authors.affiliation: School of Electrical and Computer Engineering, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Wangran
authors.initials: W
authors.lastname: Wu
authors.affiliation: School of Mechanical Engineering, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Luo
authors.affiliation: School of Mechanical Engineering, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Xianfan
authors.initials: X
authors.lastname: Xu
authors.affiliation: School of Electrical and Computer Engineering, Purdue University , West Lafayette, Indiana 47907, United States.|Birck Nanotechnology Center, Purdue University , West Lafayette, Indiana 47907, United States.
authors.forename: Peide D
authors.initials: PD
authors.lastname: Ye
keywords: DFT calculations; Raman spectroscopy; black phosphorus; negative Poisson’s ratio; strain