  Hexagonal boron nitride (hBN) is a natural hyperbolic material that supports
both volume-confined hyperbolic polaritons (HPs) and sidewall-confined
hyperbolic surface polaritons (HSPs). In this work, we demonstrate effective
excitation, control and steering of HSPs in hBN through engineering the
geometry and orientation of hBN sidewalls. By combining infrared (IR)
nano-imaging and numerical simulations, we investigate the reflection,
transmission and scattering of HSPs at the hBN corners with various apex
angles. We show that the sidewall-confined nature of HSPs enables a high degree
of control over their propagation by designing the geometry of hBN
nanostructures.
