Investigation of possible quantized circular photogalvanic effect in chiral multifold semimetals RhSi and CoSi*

One of the most exciting phenomena from a single Weyl/multifold node in response to the electromagnetic wave is the quantized circular photogalvanic effect (CPGE), where a universal photo-current generation rate is expected regardless of the light frequency. By doing the terahertz emission measurement with widely tunable excitation energy from 0.2 to 1.1 eV, we exam two candidates for the quantized CPGE, RhSi and CoSi. We find both materials show giant but non-quantized CPGE. Combining the experimental results with density functional theory calculations, we explain the origins for the absence of the quantization and further propose to reach quantized CPGE in these two compounds by altering the Fermi level and increasing the hot-carrier lifetime. References: Ni, et al. arXiv. arXiv:2006.09612; Ni, et al. arXiv:2005.13473; Xu, et al. PNAS 10.1073/pnas.2010752117 (2020).