We show the existence of an inherent property of evanescent electromagnetic waves: spin-momentum locking, where the direction of momentum fundamentally locks the polarization of the wave. We trace the ultimate origin of this phenomenon to complex dispersion and causality requirements on evanescent waves. We demonstrate that every case of evanescent waves in total internal reflection, surface states and optical fibers/waveguides possesses this intrinsic spin-momentum locking. We also introduce a universal right-handed triplet consisting of momentum, decay and spin for evanescent waves. We derive the Stokes parameters for evanescent waves which reveal an intriguing result - every fast decaying evanescent wave is inherently circularly polarized with its handedness tied to the direction of propagation. We also show the existence of a fundamental angle associated with total internal reflection (TIR) such that propagating waves locally inherit perfect circular polarized characteristics from the evanescent wave. This circular TIR condition occurs if and only if the ratio of permittivities of the two dielectric media exceeds the golden ratio. Our work leads to a unified understanding of this spin-momentum locking in various nanophotonic experiments and sheds light on the electromagnetic analogy with the quantum spin hall state for electrons.
Spin-momentum locking of polariton edge states in honeycomb lattices
Universidad Autónoma de Madrid（马德里自治大学）；Università di Padova（帕多瓦大学）；Indian Institute of Technology Bombay（孟买印度理工学院）；Indian Institute of Technology Dharwad（达尔瓦德印度理工学院）；Julius-Maximilians-Universität Würzburg（维尔茨堡朱利叶斯-马克西米利安大学）
Spin-Split Dispersion of Leaky Surface plasmons in Inversion- Symmetric System
Indian Institute of Science Education and Research Kolkata（印度科学教育研究所加尔各答分校）；Indian Institute of Technology Kanpur（坎普尔印度理工学院）；Swiss Federal Institute of Technology Lausanne (EPFL)（洛桑联邦理工学院（瑞士联邦理工学院））；Tata Centre for Interdisciplinary Sciences, TIFRH（塔塔跨学科科学中心，海德拉巴泰戈尔研究所）
