Optical investigation of topological semimetal SrMnSb₂

We investigate the temperature-dependent infrared spectroscopy of SrMnSb₂, which is a semimetal with multiple Fermi surfaces. A notable blue shift of the plasma minimum in reflectivity upon cooling indicates that the carrier density varies with temperature. In the real part of the optical conductivity σ₁(ω), a linearly-increased component which extrapolates to zero conductivity at finite frequency has been identified, which suggests dispersion of gapped Dirac band structures near the Fermi level. A two-Drude model, representing two different types of carriers, is introduced to describe the real part of optical conductivity. We separate the contributions of two-Drude model in dc conductivity, and demonstrate that the transport properties of SrMnSb₂ are mainly affected by the narrow-Drude quasiparticles. Compared with the similar phenomena observed in CaMnSb₂ and SrMnBi₂, we can infer that the two-Drude model is an appropriate approach to investigate the multiband materials in AMnSb₂ and AMnBi₂ families.