English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

Vortex, the winding of a vector field in two dimensions, has its core thefield singularity and its topological charge defined by the quantized windingangle of the vector field. Vortices are one of the most fundamental topologicalexcitations in nature, widely known in hair whorls as the winding of hairstrings, in fluid dynamics as the winding of velocities, in angular-momentumbeams as the winding of phase angle and in superconductors and superfluids asthe winding of order parameters. Nevertheless, vortices have hardly beenobserved other than those in the real space. Although band degeneracies, suchas Dirac cones, can be viewed as momentum-space vortices in their mathematicalstructures, there lacks a well-defined physical observable whose winding numberis an arbitrary signed integer. Here, we experimentally observed momentum-spacevortices as the winding of far-field polarization vectors in the Brillouin zone(BZ) of periodic plasmonic structures. Using a home-made polarization-resolvedmomentum-space imaging spectroscopy, we completely map out the dispersion,lifetime and polarization of all radiative states at the visible wavelengths.The momentum space vortices were experimentally identified by their windingpatterns in the polarization-resolved iso-frequency contours and theirdiverging radiative quality factors. Such polarization vortices can existrobustly on any periodic systems of vectorial fields, while they are notcaptured by the existing topological band theory developed for scaler fields.This work opens up a promising avenue for exploring topological photonics inthe momentum space, studying bound states in continuum (BICs), as well as forrendering and steering vector beams and designing high-Q plasmonic resonances.

Observation of optical vortices in momentum space