Chiral topological semimetals are materials that break both inversion and mirror symmetries. They host interesting phenomena such as the quantized circular photogalvanic effect (CPGE) and the chiral magnetic effect. In this work, we report a comprehensive theoretical and experimental analysis of the linear and nonlinear optical responses of the chiral topological semimetal RhSi, which is known to host multifold fermions. We show that the characteristic features of the optical conductivity, which display two distinct quasi-linear regimes above and below 0.4 eV, can be linked to excitations of different kinds of multifold fermions. The characteristic features of the CPGE, which displays a sign change at 0.4 eV and a large non-quantized response peak of around 160 μA/V² at 0.7 eV, are explained by assuming that the chemical potential crosses a flat hole band at the Brillouin zone center. Our theory predicts that, in order to observe a quantized CPGE in RhSi, it is necessary to increase the chemical potential as well as the quasiparticle lifetime. More broadly, our methodology, especially the development of the broadband terahertz emission spectroscopy, could be widely applied to study photogalvanic effects in noncentrosymmetric materials and in topological insulators in a contact-less way and accelerate the technological development of efficient infrared detectors based on topological semimetals.

手性拓扑半金属是破坏反型和镜像对称性的材料。它们具有有趣的现象，例如定量圆形光电动效应（CPGE）和手性磁效应。在这项工作中，我们报告了手性拓扑半金属RhSi的线性和非线性光学响应的​​全面理论和实验分析，RhSi已知可以容纳多重费米子。我们表明，显示出0.4 eV上下两个不同的准线性态的光导率的特征可以与不同种类的多重费米子的激发相关。CPGE的特征，在0.4 eV处显示出符号变化，并在160μA/ V ²左右具有较大的未量化响应峰通过假设化学势穿过布里渊区中心的平坦空穴带来解释0.7 eV处的峰。我们的理论预测，为了观察RhSi中的定量CPGE，有必要增加化学势以及准粒子寿命。更广泛地说，我们的方法，尤其是宽带太赫兹发射光谱学的发展，可以广泛地用于以非接触方式研究非中心对称材料和拓扑绝缘体中的光电效应，并加速基于拓扑半金属的高效红外探测器的技术发展。 。