Surface plasmons play a key role in nanophotonics as they enable light manipulation at subwavelength scales. Active control of surface plasmon properties of a device is, however, more difficult to achieve. One of the mechanisms studied to achieve this control are structural phase changes of the active material, such as solid to liquid transitions. S. R. C. Vivekchand and colleagues have now demonstrated an advantage of this strategy by observing that light can couple to surface plasmons better for a liquid metal than for a solid. The metal studied, gallium, has a relatively low melting point of just below 303 K. This makes it easy to compare the optical properties of grating structures for liquid and solidified structures. The liquid phase showed a much stronger light absorption at plasmon resonances. This is because of a broadening of the electronic band structure in the liquid phase that reduces losses for the surface plasmons. The reflective properties can therefore be efficiently controlled simply by heating and cooling the device.
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Heber, J. Plasmonics making waves. Nature Mater 11, 745 (2012). https://doi.org/10.1038/nmat3418