Launching and Manipulation of Higher-Order In-Plane Hyperbolic Phonon Polaritons in Low-Dimensional Heterostructures

G. Lu, Z. Pan, C. R. Gubbin, R. A. Kowalski, S. De Liberato, D. Li and J. D. Caldwell

Advanced Materials 2300301 (2023)
Hyperbolic phonon polaritons (HPhPs) are stimulated by coupling infrared (IR) photons with the polar lattice vibrations. Such HPhPs offer low-loss, highly confined light propagation at subwavelength scales with out-of-plane or in-plane hyperbolic wavefronts. For HPhPs, while a hyperbolic dispersion implies multiple propagating modes with a distribution of wavevectors at a given frequency, so far it has been challenging to experimentally launch and probe the higher-order modes that offer stronger wavelength compression, especially for in-plane HPhPs. In this work, we report the experimental observation of higher-order in-plane HPhP modes stimulated on a 3C-SiC nanowire (NW)/α-MoO3 heterostructure where leveraging both the low-dimensionality and low-loss nature of the polar NWs, higher-order HPhPs modes within two-dimensional α-MoO3 crystal are launched by the one-dimensional 3C-SiC NW. We further study the launching mechanism and determine the requirements for efficiently launching of such higher-order modes. In addition, by altering the geometric orientation between the 3C-SiC NW and α-MoO3 crystal, we demonstrate the manipulation of higher-order HPhP dispersions as a method of tuning. This work illustrates an extremely anisotropic low dimensional heterostructure platform to confine and configure electromagnetic waves at the deep-subwavelength scales for a range of infrared applications including sensing, nano-imaging, and on-chip photonics.