We have studied the charge dynamics for the layered polar Dirac semimetal ${\mathrm{BaMnSb}}_2$ by means of optical spectroscopy and ab initio calculation. A large anisotropy in the optical conductivity spectra is observed for two orthogonal light polarizations $E^{\omega }$, both of which are perpendicular to the stacking direction of monoatomic layers; a clear peak emerges at the absorption edge of the Dirac band for $E^{\omega }$ parallel to the zigzag chain in the distorted Sb square net, but a tiny kink is observed for $E^{\omega }$ perpendicular to the chain. We also found that the effective electron mass is about an order of magnitude larger in the direction perpendicular to the chain than parallel to it. The theoretical calculation suggests that the dispersion of the Dirac band perpendicular to the chain is suppressed due to the reduced orbital hybridization, leading to the large in-plane electronic anisotropy.

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• Topological materials
• Semimetals
• Infrared spectroscopy