@article {Chaudharyeaau7171,
	title = {Engineering phonon polaritons in van der Waals heterostructures to enhance in-plane optical anisotropy},
	journal = {Science Advances},
	volume = {5},
	number = {4},
	year = {2019},
	publisher = {American Association for the Advancement of Science},
	abstract = {Van der Waals (vdW) heterostructures assembled from layers of two-dimensional 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 phosphorus (h-BN/BP) heterostructures, demonstrating the first direct observation of in-plane anisotropic phonon polariton modes in vdW heterostructures. Notably, the measured in-plane optical anisotropy along the 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 αmax = 1.25 in the frequency spectrum at 1405 to 1440 cm-1. These results provide new insights into 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.},
	doi = {10.1126/sciadv.aau7171},
	url = {https://advances.sciencemag.org/content/5/4/eaau7171},
	author = {Kundan Chaudhary and Tamagnone, Michele and Rezaee, Mehdi and Bediako, D. Kwabena and Ambrosio, Antonio and Philip Kim and Capasso, Federico}
}
