Optical conductivity and band gap in the double-Weyl candidate <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>SrSi</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math> at ambient pressure

The authors study here the possible double-Weyl state in cubic SrSi${}_{2}$ using optical spectroscopy and $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations. The free-carrier density, found from optics, decreases with decreasing temperature, consistent with an activation behavior. Experimental interband conductivity juxtaposed with $a\phantom{\rule{0}{0ex}}b$ $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}o$ calculations shows that conventional density functional theory fails to describe the electronic structure of SrSi${}_{2}$ near the Fermi level. A semilocal exchange-correlation potential allows a much better agreement with the experiment, resulting a gapped band structure of SrSi${}_{2}$ with the direct gap of 35--40 meV.