title: Electromagnetic stress at the boundary: Photon pressure or tension?
abstract: It is well known that incident photons carrying momentum ℏk exert a positive photon pressure. But if light is impinging from a negative refractive medium in which ℏk is directed toward the source of radiation, should light exert a photon "tension" instead of a photon pressure? Using an ab initio method that takes the underlying microstructure of a material into account, we find that when an electromagnetic wave propagates from one material into another, the electromagnetic stress at the boundary is, in fact, indeterminate if only the macroscopic parameters are specified. Light can either pull or push the boundary, depending not only on the macroscopic parameters but also on the microscopic lattice structure of the polarizable units that constitute the medium. Within the context of an effective-medium approach, the lattice effect is attributed to electrostriction and magnetostriction, which can be accounted for by the Helmholtz stress tensor if we use the macroscopic fields to calculate the boundary optical stress.
authors.affiliation: Department of Physics and Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: Shubo
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Physics and Institute of Computational and Theoretical Studies, Hong Kong Baptist University, Hong Kong, China.
authors.forename: Jack
authors.initials: J
authors.lastname: Ng
authors.affiliation: Department of Physics and Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: Meng
authors.identifier: 0000-0002-2087-3007
authors.initials: M
authors.lastname: Xiao
authors.affiliation: Department of Physics and Institute for Advanced Study, The Hong Kong University of Science and Technology, Hong Kong, China.
authors.forename: Che Ting
authors.initials: CT
authors.lastname: Chan
mesh_terms: D000465:Algorithms; D055590:Electromagnetic Phenomena; D008962:Models, Theoretical; D017785:Photons
keywords: Photon pressure; effective medium; electromagnetic stress; metamaterial; negative-refractive-index material; optical pulling force