Periodic Reporting for period 1 - SGPCM (Switching graphene-plasmon with phase-change materials)
Reporting period: 2017-01-01 to 2018-12-31
The project “SGPCM” aimed to image, control and switch the propagation of graphene plasmon polaritons with the help of controlling the structural phase of a phase change material (PCM), particularly chalcogenide the GeSbTe (GST) alloy, which could provide the basic understanding for developing non-volatile switchable, ultracompact plasmonic devices. Moreover, the project aimed on exploring polaritons and their potential applications in other two dimensional (2D) materials and nanostructures made out of them, such as phonon polaritons in hexagonal boron nitride (hBN).
Within the project, the researcher developed the very first hyperbolic mid-infrared metasurface by nanostructuring a thin layer of hBN that supports deep subwavelength-scale phonon polaritons that propagate with in-plane hyperbolic dispersion. He designed the metasurface and used s-SNOM to visualize the concave (anomalous) wavefronts of a diverging polariton beam, which represent a landmark feature of hyperbolic polaritons. The results of this work illustrate how near-field microscopy can be applied to reveal the exotic wavefronts of polaritons in anisotropic materials and demonstrate that nanostructured van der Waals materials can form a highly variable and compact platform for hyperbolic infrared metasurface devices and circuits. (Science 359, 892 (2018))
Furthermore, the researcher has also contributed to three other high-impact publications that are related to polariton manipulation (although not via PCM). First, he has participated a work that leads to the discovery of anisotropic phonon polariton propagation along the surface of α-MoO3, a natural van der Waals material. This work verified phonon polaritons with elliptic and hyperbolic in-plane dispersion, as well as with ultra-low losses, which could enable directional and strong light–matter interactions, nanoscale directional energy transfer and integrated flat optics in applications ranging from bio-sensing to quantum nanophotonics. (Nature, 562, 557–562 (2018))
Second, the researcher has participated in a study on resonating surface phonon polaritons in linear hBN antennas. He contributed to the understanding that the antenna resonances are based on waveguide modes originating from the hybridization of hyperbolic surface phonon polaritons that propagate along the edges of the hBN waveguide. This work establishes the basis for the understanding and design of linear waveguides, resonators, sensors and metasurface elements based on hyperbolic 2D materials and metamaterials. (Nature Communications, 8, 15624 (2017))
Third, the researcher also contributed in the first demonstration of surface-enhanced infrared absorption (SEIRA) spectroscopy exploiting well-defined, grating of hBN nanoribbon supporting phonon polaritons. He performed numerical simulations to interpret the measured data and understand the underlying physics. The realization of “phononic SEIRA” could become a highly interesting platform for molecular sensing, and even more exciting, for fundamental studies of vibrational strong coupling at the nanoscale. The results open the door for many infrared photonic applications, such as ultra-small high-quality infrared resonators, for example, for field-enhanced infrared spectroscopy. (Light-Science & Applications, 7, 17172 (2018))