Engineering Phonon Polaritons in van der Waals Heterostructures to Enhance In-Plane Optical Anisotropy

Abstract

Van der Waals heterostructures assembled from layers of 2D materials have attracted considerable interest due to their novel optical and electrical properties. Here we report a scattering-type scanning near field optical microscopy study of hexagonal boron nitride on black phosphorous (h-BN/BP) heterostructures, demonstrating the first direct observation of in-plane anisotropic phonon polariton modes in vdW heterostructures. Strikingly, the measured in-plane optical anisotropy along armchair and zigzag crystal axes exceeds the ratio of refractive indices of BP in the x-y plane. We explain that this enhancement is due to the high confinement of the phonon polaritons in h-BN. We observe a maximum in-plane optical anisotropy of α_max=1.25 in the 1405-1440 cm-1 frequency spectrum. These results provide new insights on the behavior of polaritons in vdW heterostructures, and the observed anisotropy enhancement paves the way to novel nanophotonic devices and to a new way to characterize optical anisotropy in thin films.

References in corpus (10)

• Rediscovering Black Phosphorus: A Unique Anisotropic 2D Material for Optoelectronics and Electronics
• Two-Dimensional Material Nanophotonics
• Gate-tuning of graphene plasmons revealed by infrared nano-imaging
• Optical nano-imaging of gate-tuneable graphene plasmons
• The Renaissance of Black Phosphorus
• Sub-diffractional, volume-confined polaritons in a natural hyperbolic material: hexagonal boron nitride
• Hyperbolic phonon-polaritons in boron nitride for near-field optical imaging
• Infrared hyperbolic metasurface based on nanostructured van der Waals materials
• Ultra-low-loss Polaritons in Isotopically Pure Materials: A New Approach
• Tunable light-matter interaction and the role of hyperbolicity in graphene-hBN system