Signatures of van Hove singularities in the anisotropic in-plane optical conductivity of the topological semimetal Nb3SiTe6

We present a temperature-dependent infrared spectroscopy study on the layered topological semimetal ${\mathrm{Nb}}_{3}{\mathrm{SiTe}}_{6}$ combined with density-functional theory calculations of the electronic band structure and optical conductivity. Our results reveal an anisotropic behavior of the in-plane ($ac$-plane) optical conductivity, with three pronounced excitations located at around 0.15, 0.28, and 0.41 eV for the polarization of the incident radiation along the $c$ axis. These excitations are well reproduced in the theoretical spectra. Based on the ab initio results, the excitations around 0.15 and 0.28 eV are interpreted as fingerprints of van Hove singularities in the electronic band structure and compared to the findings for other topological semimetals.