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.