Raman scattering spectroscopy as a probe of magnetic Weyl semimetal.

Experimental spectroscopic probe of electronic band structure close to the Fermi energy in order to prove an existence of Weyl nodes presents a challenge due to a need for high spectral resolution. Here we propose electronic Raman scattering (χ"(ω)) as a probe of Weyl nodes. In Weyl semimetal candidate Nd₂Ir₂O₇ TRS breaking at T_N=35 K is suggested to split a quadratic node into pairs of Weyl nodes. Experimentally, we observe an abrupt decrease of  χ"(ω) below 20 meV at T_N. Our calculations of Raman scattering response of Weyl semimetals suggest two components of scattering. In semimetals, electronic scattering by quasiparticles possessing finite life is proportional to the electronic DOS. In Weyl semimetals, an additional non-zero contribution of scattering specific to the Weyl nodes originates from Berry flux, which necessarily introduces a momentum shift, resulting in a  χ"(ω)~ω²  frequency dependence. We discuss a correspondence of the low frequency  χ"(ω) in Nd₂Ir₂O₇ spectra  to the theoretical predictions for Weyl semimetal.