Anisotropic electrodynamics of type-II Weyl semimetal candidate WTe2

We investigated the ab-plane optical properties of single crystals of WTe2 for light polarized parallel and perpendicular to the W-chain axis over a broad range of frequency and temperature. At far-infrared frequencies, we observed a striking dependence of the reflectance edge on light polarization, corresponding to anisotropy of the carrier effective masses. We quantitatively studied the temperature dependence of the plasma frequency, revealing a modest increase of the effective mass anisotropy in the ab plane upon cooling. We also found strongly anisotropic interband transitions persisting to high photon energies. These results were analyzed by comparison with ab initio calculations. The calculated and measured plasma frequencies agree to within 10% for both polarizations, while the calculated interband conductivity shows excellent agreement with experiment.