Anisotropic Optical Conductivity of Weyl Semimetals PrAlSi and PrAlGe

PrAlSi and PrAlGe are magnetic Weyl semimetal with ferromagnetic ordering below 20 K. Questions such as the origins of magnetic interactions, the role of Berry curvature or the coupling of Weyl fermions to magnetic moments are still debated. Here, we address some of these outstanding issues through polarization dependent optical conductivity on single crystals of PrAlSi and PrAlGe. We measured reflectance at various directions of the electric field with respect to the crystallographic axes, in the spectral range from 80 cm^-1 to 24,000 cm^-1, both in the paramagnetic and ferromagnetic phases. We observed common features between PrAlSi and PrAlGe, both in terms of anisotropy and spectral weight redistribution across the magnetic transition. Our results indicate weak coupling of Weyl fermions to magnetic moments of Pr³⁺ ions, similar to some of earlier reports.