Symmetry‐Protected Photonic Chiral Spin Textures by Spin–Orbit Coupling

Abstract

Chiral spin textures are widely researched in condensed matter systems and have shown potential for use in spintronics and storage applications. Photonic counterparts of these textures are observed in various optical systems with broken inversion symmetry. Unfortunately, the resemblances are only phenomenological. This work proposes a theoretical framework based on the variational theorem to show that the photonic chiral spin textures in an optical interface originate from the system's symmetry and relativity. Analysis of the rotational symmetry in optical systems indicates that the conservation of the total angular momentum is preserved from the local variations of spin vectors. Specifically, although the integral spin momentum does not carry net energy, the local spin momentum distribution, which determines the local subluminal energy transport and minimization variation of the square of the total angular momentum, results in the chiral twisting of the local spin vectors. The findings of this study deepen the understanding of the symmetries, conservative laws, and energy transport in optical systems, reveal the similarities in the formation mechanisms and the geometries of photonic and condensed-matter chiral spin textures, and have potential applications in chiral and spin photonics.

Single-shot characterization of vector beams by generalized measurements

“…due to differential aberrations, acquired Gouy phases or effects of optical elements, leave the overall topology intact, effectively redistributing the polarization structure across the beam profile. It would be interesting to test this in a full investigation of retrieving the vector quality factor [66] and optical skyrmion number [9,67], to affirm the invariance of vectorial structured light due to dephasing and aberrations.…”

Topological quasiparticles of light: Optical skyrmions and beyond

“…Recently, an electric analogue of the DMI was demonstrated [90,91], which inspires exploration of the optical DMI. For isolated spin-skyrmions, optical analog of the exchange energy and the DMI terms were related to conservation of the total angular momentum and the spin texture stability is protected by the symmetry of the optical system [92]. This would be important for development of new optical excitations with skyrmionic dipoles or multipoles.…”

Symmetry‐Protected Spoof Localized Surface Plasmonic Skyrmion

“…Optical skyrmions were first generated by interfering multiple surface plasmon polariton waves. [11] Subsequently, many approaches have been proposed to construct optical skyrmions using different field vectors, such as the electric or magnetic field vectors of freespace or confined waves, [12][13][14][15][16] spin vectors of the evanescent EM waves, [17][18][19][20][21][22][23] synthesized Stokes vectors of paraxial vector beams, [24][25][26] and synthesized pseudospin vectors in photonic crystals, [27] etc. These optical skyrmions exhibit great topologically protected stability and deep-subwavelength features, enable new degrees of freedom to engineer structured light and light-matter interactions, and promise many applications in nanometer-and femtosecond-scale metrology, [24,28] deepsubwavelength microscopy, [18] ultrafast vector imaging, [15] and topological Hall devices.…”