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Title: Quantized circular photogalvanic effect in chiral multifold semimetals
Plain: In chiral crystals such as RhSi and CoSi, circularly polarized light should drive a current whose growth rate equals a whole number (a topological charge) times fundamental constants, and this quantization has not been confirmed.
Precise: For chiral multifold semimetals (RhSi, CoSi, PdGa), the trace of the circular photogalvanic injection tensor is predicted to be quantized, $\operatorname{tr}\beta = i \pi e^3 C / h^2$ with $C$ the Chern number of the Fermi surface around the multifold node, within the frequency window where only transitions near that node are allowed. Determine whether such a plateau exists experimentally and to what accuracy. An answer is the measured $\operatorname{tr}\beta$ in units of $\pi e^3/h^2$ with error over the predicted window.
Settled by: Broadband, absolutely calibrated terahertz-emission or photocurrent measurements showing a frequency-independent plateau at the quantized value.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: RhSi data (Rees et al. 2020) agree with the predicted magnitude in a window below 0.65 eV, but a plateau at the quantized value with stated accuracy is not established, and interaction corrections are predicted, as of 2026.
Posed since: 2017