title: OPTICS. Quantum spin Hall effect of light.
abstract: Maxwell's equations, formulated 150 years ago, ultimately describe properties of light, from classical electromagnetism to quantum and relativistic aspects. The latter ones result in remarkable geometric and topological phenomena related to the spin-1 massless nature of photons. By analyzing fundamental spin properties of Maxwell waves, we show that free-space light exhibits an intrinsic quantum spin Hall effect—surface modes with strong spin-momentum locking. These modes are evanescent waves that form, for example, surface plasmon-polaritons at vacuum-metal interfaces. Our findings illuminate the unusual transverse spin in evanescent waves and explain recent experiments that have demonstrated the transverse spin-direction locking in the excitation of surface optical modes. This deepens our understanding of Maxwell's theory, reveals analogies with topological insulators for electrons, and offers applications for robust spin-directional optical interfaces.
authors.affiliation: Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198, Japan. Nonlinear Physics Centre, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200, Australia. k.bliokh@gmail.com fnori@riken.jp.
authors.forename: Konstantin Y
authors.initials: KY
authors.lastname: Bliokh
authors.affiliation: Nonlinear Physics Centre, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200, Australia.
authors.forename: Daria
authors.initials: D
authors.lastname: Smirnova
authors.affiliation: Center for Emergent Matter Science, RIKEN, Wako-shi, Saitama 351-0198, Japan. Department of Physics, University of Michigan, Ann Arbor, MI 48109-1040, USA. k.bliokh@gmail.com fnori@riken.jp.
authors.forename: Franco
authors.initials: F
authors.lastname: Nori