University of Minnesota
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Ke Wang

Guided Modes of Anisotropic van der Waals Materials Investigated by Near-Field Scanning Optical Microscopy
D. Wintz*, K. Chaudhary*, K. Wang, L. Jauregui, A. Ambrosio, A. Y. Zhu, R. C. Devlin, M. Tamagnone, J. D. Crossno, K. Watanabe, T. Taniguchi, P. Kim, F. Capasso, ACS Photonics (2018)

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Guided modes in anisotropic two-dimensional van der Waals materials are experimentally investigated and their refractive indices in visible wavelengths are extracted. Our method involves near-field scanning optical microscopy of waveguide (transverse electric) and surface plasmon polariton (transverse magnetic) modes in h-BN/SiO2/Si and Ag/h-BN stacks, respectively. We determine the dispersion of these modes and use this relationship to extract anisotropic refractive indices of h-BN flakes. In the wavelength interval 550-700 nm, the in-plane and out-of-plane refractive indices are in the range 1.98-2.12 and 1.45-2.12, respectively. Our approach of using near-field scanning optical microscopy allows for direct study of interaction between light and two-dimensional van der Waals materials and heterostructures.