Optical investigation of tungsten diphosphide (WP2), a weyl semimetal.
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Date
2025
Authors
Nyirongo, Racheal
Journal Title
Journal ISSN
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Publisher
The University of Zambia
Abstract
The optical investigation of tungsten diphosphide (WP2), a type-II Weyl semimetal, reveals its exceptional topological and anisotropic electronic properties. Through resistivity and Fourier-transform infrared spectroscopy measurements, WP2 exhibit high conductivity and anisotropic transport behavior. Key findings include a high residual resistivity ratio (RRR) of 47,000, indicative of exceptional crystal purity and long electron mean free paths. At low temperatures, WP2 exhibits quadratic temperature-dependent resistivity, aligning with Fermi liquid theory and underscoring the minimal impurity scattering in clean samples. The optical reflectivity and conductivity of WP2 were obtained using Fourier-transform infrared spectroscopy, followed by Kramers-Kronig analysis respectively. WP2 shows strong anisotropy between its a-axis and c-axis orientations, as evidenced by differences in plasma edges i.e. 3750 cm−1 for E//c axis plane and 3600 cm−1 for E// a plane axis and in the scattering rate. Anisotropy occurs when the refractive index of a material varies with polarization or propagation direction, enabling controlled modulation of light, which can be applicable in optical switching. The study also identified distinct interband transitions and directional variations in optical responses, with enhanced carrier mobility along the a-axis compared to the c-axis. Spectral weight analysis highlights a redistribution across the midinfrared and near-infrared regions, consistent with WP2’s robust electronic structure. These results establish WP2 as a benchmark material for topological physics and a promising candidate for electronic and optoelectronic applications e.g optical switch.
Description
Thesis of Master of Science in Physics.