Two-dimensional materials with intrinsic auxeticity: progress and perspectives

Materials with a negative Poisson's ratio, termed auxetic materials, will expand (contract) in the transverse direction when they are stretched (compressed) longitudinally. They provide exciting prospects for enhancing mechanical properties and a wide range of promising applications. Driven by the current demand for nano-devices with specific functionalities, research studies on two-dimensional auxetic materials with an intrinsic negative Poisson's ratio are intensively simulated. Herein, we summarize the recent efforts and progress in material discovery and property characterization on two-dimensional auxetic materials. We categorize the rich variety of the proposed two-dimensional auxetic materials based on their structures and whether they have been synthesized experimentally. The underlying mechanisms for forming a negative Poisson's ratio as well as the modulation of negative Poisson's ratio are discussed. Finally, we close by assessing the challenges and perspectives faced by future research and development of this compelling class of materials.