Néel-type optical skyrmions inherited from evanescent electromagnetic fields with rotational symmetry

Abstract: Optical skyrmions, the optical analogue of topological configurations formed by three-dimensional vector fields covering the whole 4{\pi} solid angle but confined in a two-dimensional (2D) domain, have recently attracted growing interest due to their potential applications in high-density data transfer, storage, and processing. While the optical skyrmions have been successfully demonstrated using different field vectors in both of free-space propagating and near-field evanescent electromagnetic fields, the study on generation and control of the optical skyrmions, and their general correlation with the electromagnetic (EM) fields, are still in infancy. Here, we theoretically propose that an evanescent transverse-magnetic-polarized (TM-polarized) EM fields with rotational symmetry are actually N\'eel-type optical skyrmions of the electric field vectors. Such optical skyrmions maintain the rotation symmetry that are independent on the operation frequency and medium. Our proposal was verified by numerical simulations and real-space nano-imaging experiments performed on a graphene monolayer. Such a discovery can therefore not only further our understanding on the formation mechanisms of EM topological textures, but also provide a guideline for facile construction of EM skyrmions that may impact future information technologies.