What is it about?
The skyrmion (aka half-vortex) and spin vortex resonantly imprinted on a 2D polariton fluid undergo a continuous transformation in time. The transformation consists in a rotation in the Poincaré sphere of polarization and it is ascribed to the xy anisotropy of the device plane. This effect leads to generalized vortex states, and even to a full-reversal of the initial topology, e.g., of a lemon-skyrmion into a star-skyrmion, or of a hedgehog (radial) polarization texture into an hyperbolic texture. The effect is analogue to a waveplate device, but instead than a fixed quantity rotation, it exerts a continouos Poincaré rotation on the ultrafast time scale of tens of picosecond.
Photo by Andrew Teoh on Unsplash
Why is it important?
The skyrmion is also known as half-vortex or full-Poincaré beam. This latter word is to indicate the presence of all the states of polarization in the space texture. The continouos twist of the full-Poincaré texture extends the polarization shaping concept to structured beams, and moves the field towards the concept of full-polarization textures in both space and time.
Read the Original
This page is a summary of: Twist of generalized skyrmions and spin vortices in a polariton superfluid, Proceedings of the National Academy of Sciences, December 2016, Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1610123114.
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Skyrmion rotation from polaritonics group
We imprint a space structured vector beam comprising all polarization states, known either as full "Poincaré beam" or "skyrmion". The mapping of the polarization pattern onto the Poincaré sphere highlights how real-space circles and radii are conformally mapped to the parallels and meridians of the sphere, respectively. The ultrafast imaging of such an initial state reveals its evolution due to the xy-anisotropy splitting along preferential crystallographic or stress/strain directions. The evolution is reproduced by a numerical model (in the figure), where we report the association of a real-space circular corona to a "topological belt". The fundamental effect of the xy-anisotropy consists in the dynamical twist of the "topological belt".
Numerical star skyrmion twist from PNAS December 27, 2016 113 (52) 14926-14931
Supporting information from the PNAS December 27, 2016 113 (52) 14926-14931 Numerical star skyrmion twist for a value of the anisotropy χ04. The S1,2,3 Stokes degree of polarizations are plotted in the left panels over a 60×60μm2 area. Several concentric circles in real space (each represented with a different color) are conformally mapped onto the Poincaré sphere on the right panel (the l-line corresponds to the green color curve). The dynamical twist is similar for each circle, highlighting the generalized skyrmion features. At around 65ps the twist angle has reached 90∘ and the S2 and S3 distributions in real space have roughly swapped with respect to initial time. Upon longer time the twist leads to a complete reversal of the initial star skyrmion into its conjugate state, the lemon skyrmion.
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