Nanoseminar 8 October - dr. Jorik van de Groep
Speaker: dr. Jorik van de Groep (UvA - Van der Waals-Zeeman Instituut)
Title: Exciton resonance tuning in atomically-thin metasurfaces
Abstract: Optical metasurfaces comprised of judiciously designed nanostructures facilitate the control of light in ultra-thin layers to perform similar functions as conventional bulky optical elements. The highly engineerable scattering properties of resonant optical antennas underpin the operation of such metasurface-based flat optics. Thus far, the choice of antenna has been limited to shaped metallic and high-index semiconductor nanostructures that support geometrical plasmonic or Mie resonances. Whereas these resonant elements offer strong light–matter interaction and excellent control over the scattering phase and amplitude, their electrical tunability has proven to be quite limited. Here, we demonstrate how excitonic resonances in atomically thin semiconductors can be harnessed as a different, third type of resonance to create mutable, flat optics. These strong materials-based resonances are unmatched in their tunability with various external stimuli. To illustrate the concept, we first demonstrate how excitons can enhance the focusing efficiency of a millimeter-scale, patterned WS2 zone plate lens. We also show how electrical gating can completely turn on and off the exciton resonance and thereby modulate the focusing efficiency by 33%.
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