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Light fields with extraordinary structure: Plasmonic skyrmion bags

A research group at the University of Stuttgart has manipulated light through its interaction with a metal surface so that it exhibits entirely new properties. The researchers have their findings in Nature Â鶹ÒùÔºics.

"Our results add another chapter to the emerging field of skyrmion research," proclaims Prof. Harald Giessen, head of the Fourth Â鶹ÒùÔºics Institute at the University of Stuttgart, whose group achieved this breakthrough. The team demonstrated the existence of "skyrmion bags" of light on the surface of a metal layer.

A better understanding of physical phenomena

Skyrmions are a mathematical description of vortex-like structures that help researchers better understand fundamental physical relationships. In recent years, this theoretical concept has been confirmed experimentally across a wide range of areas, including magnetic solids and material surfaces.

Giessen's group has now investigated whether light impinging on the structured surface of a thin gold layer can be made to behave like skyrmion bags that follow specific symmetries. These bags consist of skyrmions contained within a larger skyrmion. For their experiment, the researchers etched fine grooves in the shape of two twisted hexagons into the gold surface with each hexagon generating a skyrmion light field.

Targeted manipulation of light fields

"We then observed a superposition of two skyrmion light fields, from which the skyrmion bags formed," explains Julian Schwab, lead author of the publication and doctoral student in Giessen's research group. Even more strikingly, the researchers were able to vary the number of skyrmions gathered within the skyrmion bags by adjusting the degree to which the light fields were twisted relative to one another.

In other words, the researchers can manipulate light fields in a targeted manner, thereby giving them shapes that usually do not occur. For the experimental verification, Giessen's team collaborated with a research group at the University of Duisburg-Essen, and for the theoretical description of the phenomenon, with a group at the Technion in Haifa.

Fundamental research with application potential

So far, this is still fundamental physics. However, these light-field skyrmions exhibit extraordinary properties, thereby sparking researchers' imagination in terms of potential technical applications. Whether the gold surface used by Giessen's team is suitable for this purpose remains to be seen.

"If someone finds a suitable material, our concept could be applied in microscopy," states Giessen. We could achieve resolutions with specialized microscopes that would otherwise be impossible because of the limits set by the wavelength of the light.