Giant optical anisotropy and visible-frequency epsilon-near-zero in hyperbolic van der Waals MoOCl2
Authors
Georgy Ermolaev, Adilet Toksumakov, Aleksandr Slavich, Anton Minnekhanov, Gleb Tselikov, Arslan Mazitov, Ivan Kruglov, Gleb Tikhonowski, Mikhail Mironov, Ilya Radko, Dmitriy Grudinin, Andrey Vyshnevyy, Zdeněk Sofer, Aleksey Arsenin, Kostya S. Novoselov, Valentyn Volkov
Categories
Abstract
The realization of extreme optical anisotropy is foundational to nanoscale light manipulation. Van der Waals (vdW) crystal MoOCl2 has emerged as a promising candidate for this quest, hosting hyperbolic plasmon polaritons in the visible and near-infrared wavelengths. However, the fundamental anisotropic dielectric tensor governing this behavior has remained elusive. Here, we resolve this problem by providing the first experimental determination of the full dielectric tensor of hyperbolic vdW MoOCl2. Via spectroscopic ellipsometry, Mueller matrix, and reflectance measurements, we quantify the material's optical duality: a metallic optical response (ε_1 < 0) along the crystallographic a-axis and a dielectric response (ε_1 > 0) along the orthogonal directions. This dichotomy drives an epsilon-near-zero (ENZ) condition at \approx 512 nm and results in giant in-plane birefringence of δn \approx 2.2 for MoOCl2. As a result, our work provides the critical missing experimental parameters for MoOCl2, establishing it as a benchmark hyperbolic and ENZ material.
Giant optical anisotropy and visible-frequency epsilon-near-zero in hyperbolic van der Waals MoOCl2
Categories
Abstract
The realization of extreme optical anisotropy is foundational to nanoscale light manipulation. Van der Waals (vdW) crystal MoOCl2 has emerged as a promising candidate for this quest, hosting hyperbolic plasmon polaritons in the visible and near-infrared wavelengths. However, the fundamental anisotropic dielectric tensor governing this behavior has remained elusive. Here, we resolve this problem by providing the first experimental determination of the full dielectric tensor of hyperbolic vdW MoOCl2. Via spectroscopic ellipsometry, Mueller matrix, and reflectance measurements, we quantify the material's optical duality: a metallic optical response (ε_1 < 0) along the crystallographic a-axis and a dielectric response (ε_1 > 0) along the orthogonal directions. This dichotomy drives an epsilon-near-zero (ENZ) condition at \approx 512 nm and results in giant in-plane birefringence of δn \approx 2.2 for MoOCl2. As a result, our work provides the critical missing experimental parameters for MoOCl2, establishing it as a benchmark hyperbolic and ENZ material.
Authors
Georgy Ermolaev, Adilet Toksumakov, Aleksandr Slavich et al. (+13 more)
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