Resonant THz spectroscopy of Weyl semimetals

CeCoGe₃ is a material that has it all: It is a Weyl semimetal and a heavy-Fermion material, with three low-temperature antiferromagnetic transitions and pressure-induced superconductivity. What makes it specifically interesting in the THz range is that the strong correlations that lead to the hybridized Kondo state, actually push the Weyl nodal lines extremely close to the Fermi level. This brings the Weyl nodal lines within reach of resonant THz excitation. In this work, this is exploited to probe the anomalous electronic features associated with Weyl nodal lines with THz time-domain spectroscopy. Remarkably it is found that these features persist all the way up to room temperature and are not washed out by thermal broadening of electronic density of states. This is likely due to the extreme low-energy THz excitation towards these nodal lines. Within this energy range, no new electronic transitions appear even at room temperature, and the anomalous Weyl conductivity therefore remains protected.