Dynamical conductivity in multiply-degenerate point-nodal semimetal CoSi

We investigate the dynamical conductivity in multiply-degenerate point-nodal semimetal CoSi by using first-principles band calculation and linear response theory. The semimetal holds point nodes in the electronic band structure. Around the nodes, electronic states are represented as multi-fold chiral fermions. We find some characteristic structures associated with the electronic structure in the spectrum of dynamical conductivity as a function of the photon frequency. Especially in the low-frequency region, a dip structure and a flat-top peak are ascribable to the electronic property of the chiral fermion and the effect of spin-orbit coupling, respectively. The numerical result can provides the relation between the profile of dynamical conductivity and electronic states in the point-nodal semimetal.