We probe the possible double-Weyl state in cubic ${\mathrm{SrSi}}_2$ using optical spectroscopy. The complex optical conductivity was measured in a frequency range from 70 to 22 000 ${\mathrm{cm}}^{-1}$ at temperatures down to 10 K at ambient pressure. The optical response of ${\mathrm{SrSi}}_2$ can be well separated into the intraband (free carriers) and interband contributions. Additionally, four infrared-active phonons are detected. As follows from the optical spectra, the free-carrier density decreases with decreasing temperature, consistent with an activation behavior. Experimental interband conductivity juxtaposed with ab initio calculations shows that conventional density-functional theory fails to describe the electronic structure of ${\mathrm{SrSi}}_2$ in the vicinity of the Fermi level. A semilocal exchange-correlation potential allows a much better agreement with the experiment, resulting in the trivial (gapped) band structure of ${\mathrm{SrSi}}_2$. The direct gap estimated from the measurements is approximately 40 meV.

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• Electronic structure
• Optical conductivity
• Narrow band gap systems
• Semimetals
• Weyl semimetal
• Density functional theory
• Fourier transform infrared spectroscopy