Abstract
Metasurfaces control light propagation at the nanoscale for applications in both free-space and surface-confined geometries. However, dynamically changing the properties of metasurfaces can be a major challenge. Here we demonstrate a reconfigurable hyperbolic metasurface comprised of a heterostructure of isotopically enriched hexagonal boron nitride (hBN) in direct contact with the phase-change material (PCM) single-crystal vanadium dioxide (VO2). Metallic and dielectric domains in VO2 provide spatially localized changes in the local dielectric environment, enabling launching, reflection, and transmission of hyperbolic phonon polaritons (HPhPs) at the PCM domain boundaries, and tuning the wavelength of HPhPs propagating in hBN over these domains by a factor of 1.6. We show that this system supports in-plane HPhP refraction, thus providing a prototype for a class of planar refractive optics. This approach offers reconfigurable control of in-plane HPhP propagation and exemplifies a generalizable framework based on combining hyperbolic media and PCMs to design optical functionality.
Highlights
Metasurfaces control light propagation at the nanoscale for applications in both free-space and surface-confined geometries
In sSNOM images, hyperbolic phonon polaritons (HPhPs) can be observed in two ways: first, polaritons launched by the light scattered from the scattering-type scanning near-field optical microscopy (s-SNOM) tip propagate to and reflect back from sample boundaries creating interference fringes with spacing λp/2, which are scattered back to free space by the tip and detected[21,32,33]
We have experimentally demonstrated that the dispersion of HPhPs can be controlled using the permittivity changes inherent in the different phases of phase-change material (PCM)
Summary
Metasurfaces control light propagation at the nanoscale for applications in both free-space and surface-confined geometries. We show this to be the case, and that the difference in the local dielectric environment between the metallic and dielectric domains results in a large change in the HPhP wavelength in the hBN over each domain, which in turn results in the refraction of the polariton when transmitting across the PCM phase-domain boundaries This means that the combination of hyperbolic media and PCMs employed here can be used to create refractive optical elements and waveguides[27], as well as components benefitting from full optical functionalities that to this point have been limited to far-field optics. By exploiting the increasingly wide range of different PCMs and hyperbolic materials and metamaterials, such as transition metal oxides[31], these effects can be realized over an extended range of frequencies
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