The Low Energy Second Harmonic Generation Spectrum of the Chiral Multifold Fermion System RhSi

Lacking any mirror symmetries, the Weyl nodes of the multifold fermion system RhSi are offset in energy, permitting a spectroscopic study of the optical properties of a single node. The lack of any mirror symmetry also implies that RhSi lacks an inversion center and thus can support second order nonlinear optical processes in its bulk. Here, we present a spectroscopic study of one of these processes, the bulk second harmonic generation response as a function of incidence photon energy and measure the single SHG susceptibility tensor element χ_xyz over the 275 - 900 meV range. We describe how our results directly probe the nonlinear optical response of the isolated Weyl at the Γ point in the Brillouin zone and discuss our findings in the context of the linear optical response of the material.