Abstract
Abstract Photonic skyrmions have applications in many areas, including the vectorial and chiral optics, optical manipulation, deep-subwavelength imaging and nanometrology. Much effort has been focused on the experimental characterization of photonic skyrmions. Here, we give an insight into the spin and orbital features of photonic skyrmions constructed by the p-polarized and s-polarized surface waves at an interface with various electric and magnetic properties by analyzing the continuity of chirality, energy flow and momentum densities through the electric and magnetic interface. The continuity of chirality density indicates that the photonic skyrmion has a property of the optical transverse spin. Most importantly, the continuity of energy flow and momentum densities results in four spin–orbit interaction quantities, which indicate the gradient of electric polarizability or permeability governs the spin–orbit interaction of photonic skyrmions and leads to the discontinuity and even the reversal of spin orientation through the optical interface. Our investigations on the spin–orbit properties of photonic skyrmions, which can give rise to the spin-dependent force and topological unidirectional transportation, is thorough and can be extended to other classical wave, such as acoustic and fluid waves. The findings help in understanding the spin–orbit feature of photonic topological texture and in constructing further optical manipulation, sensing, quantum and topological techniques.
Highlights
Light carries spin angular momentum (SAM) and orbital angular momentum (OAM) [1,2,3,4,5,6]
For the photonic skyrmion constructed by the p-polarized surface wave, the directions of energy flow density (EFD) and spin vector would be reversal due to the inverse of permittivity through the interface, whereas the momentum density (MD) reverse owing to the opposite magnetic permeability in the two sides of interface
By considering the chirality feature of photonic skyrmion, we find that the time-averaging chirality density of photonic skyrmion vanishes, which means that this spin texture is constituted by the optical transverse spin
Summary
Light carries spin angular momentum (SAM) and orbital angular momentum (OAM) [1,2,3,4,5,6]. For photonic skyrmions constructed by the p-polarized surface waves, the electric polarizability related term governs the spin–orbit interaction of surface waves and results in the EFD reversal and an inverted outof-plane orientation of spin texture through the optical interface. If a variation of permeability is introduced into the material in lower half-space, the magnetic susceptibility related term would lead to the MD reverse and the accompanied in-plane orientation of spin texture through the optical interface. This theoretical analysis, which is thorough and can be extended to the other classical waves, helps in understanding the spin–orbit features of photonic skyrmions and in constructing further optical manipulation, sensing, quantum and topological techniques
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