Dirac nodal lines in the optical conductivity of Ba(Co,Ni)S₂

The solid solution between BaCoS₂ and BaNiS₂ shows anarray of quantum properties. The Co material is a semi-metal dominated by strong correlations. At 28% Ni doping it undergoes an electronic metal-insulator phase transition to a Drude metal. The metallic states persists all the way to the pure Ni compound, where bands with a linear dispersion producing dispersive Dirac nodal lines compete with the bulk Drude carriers. We combined ab-initio calculations with mesurements of the optical conductivity of these materials to reverse engineer the contribution of each band in the optical response of these materials. We explained uncommon features in their optical response such as a linear dispersion of the optical conductivity [1] and the existence of an isosbestic line separating a spectral-weight transfer across Dirac nodal states [2].