Free-carrier dynamics in Au₂Pb probed by optical conductivity measurements

We measured the optical reflectivity of the Dirac material Au₂Pb in a broad frequency range (30-48 000 cm^-1) for temperatures between 9 and 300 K. The optical conductivity, computed from the reflectivity, is dominated by free-carrier contributions from topologically trivial bulk bands at all temperatures. The temperature-independent total plasma frequency of these carriers is eV. Overall, optical response of Au₂Pb is typically metallic with no signs of localization and bad-metal behavior.