Fig. 3. Room tempreture CPGE spectrum, optical conductivity and band structure for CoSi.

a Measured second-order CPGE photo-conductivity (β_xxτ) as a function of incident photon energy, and ab-intio calculations of the CPGE current with and without spin-orbit coupling at room temperature. b The band structure of CoSi without spin-orbit coupling. We define zero energy at the threefold node at the Γ point. The double Weyl node at the R point is at −185 meV. The dashed horizontal line indicates the chemical potential E_f = −37 meV in our sample, moderately lower from that obtained by DFT (E_f = −20 meV). The band structure of the k ⋅ p model is shown in green (band 1), blue (band 2), and orange (band 3) obtained by fitting the ab-intio band structure (black) up to quadratic corrections. For the Γ−X direction we define ${\omega }_1^X$, ${\omega }_2^X$, and ${\omega }_3^X$ as the minimum energy that allows transitions from band 1 to band 2, the maximum energy that allows transition from band 1 to band 2 and the minimum energy that allows transitions from band 2 to band 3, respectively. We define in the same way ${\omega }_1^R$ in the R direction (${\omega }_{2,3}^R$ fall outside the applicability of the quadratic model). c Total (gold) and interband (blue) optical conductivity of CoSi at 300 K. d Momentum resolved contributions to the CPGE peak at 0.4 eV in the red curve in a.