Nanoimaging of resonating hyperbolic polaritons in linear boron nitride antennas
F.J. Alfaro-Mozaz, P. Alonso-Gonzalez, S. Velez, I. Dolado, M. Autore, S. Mastel, F. Casanova, L.E. Hueso, P. Li , A.Y. Nikitin, and R. Hillenbrand
Nature Communications 8, 15624 (2017)
Polaritons in layered materials—including van der Waals materials—exhibit hyperbolic
dispersion and strong field confinement, which makes them highly attractive for applications
including optical nanofocusing, sensing and control of spontaneous emission. Here we report
a near-field study of polaritonic Fabry–Perot resonances in linear antennas made of a
hyperbolic material. Specifically, we study hyperbolic phonon–polaritons in rectangular
waveguide antennas made of hexagonal boron nitride (h-BN, a prototypical van der Waals
crystal). Infrared nanospectroscopy and nanoimaging experiments reveal sharp resonances
with large quality factors around 100, exhibiting atypical modal near-field patterns that have
no analogue in conventional linear antennas. By performing a detailed mode analysis, we can
assign the antenna resonances to a single waveguide mode originating from the hybridization
of hyperbolic surface phonon–polaritons (Dyakonov polaritons) that propagate along the
edges of the h-BN waveguide. Our work establishes the basis for the understanding and
design of linear waveguides, resonators, sensors and metasurface elements based on
hyperbolic materials and metamaterials.