Deep-subwavelength features of photonic skyrmions in a confined electromagnetic field with orbital angular momentum

In magnetic materials, skyrmions are nanoscale regions where the orientation of the electron spin changes in a vortex-type manner(1-4). Electromagnetic waves carry both spin and orbital angular momenta(5,6). Here we show that spin-orbit coupling(7-12) in a focused vector beam results in a skyrmion-like structure of local photonic spin. While diffraction limits the spatial size of intensity variations, the direction of the electromagnetic field, which defines the polarization and local photonic spin state, is not subject to this limitation. We demonstrate that the local spin direction in the skyrmion-like structure varies on the deep-subwavelength scale down to 1/60 of the light wavelength, which corresponds to a length scale of about 10 nm. The application of photonic skyrmions may range from high-resolution imaging and precision metrology to quantum technologies and data storage where the local spin state of the field, not its intensity, can be applied to achieve deep-subwavelength optical patterns.