Anisotropic Circular Photogalvanic Response in Chiral Weyl Semimetal RhSi

Weyl semimetals have been a hot topic in the condensed matter physics community due to their unconventional linear band crossing from the bulk characters. Breaking of time-reversal or inversion symmetry allows Dirac fermions to split into a pair of Weyl fermions with an opposite chirality at a non-high symmetry point in momentum space. The circular photogalvanic effect in which the incident helicity determines the generated current vector is direct evidence from the topology and band structure of the chiral Weyl semimetals. Notably, in optical transition near a Weyl node, it has recently been predicted that the magnitude of the CPGE is associated with its monopole charge. Since the nodes with opposite charges are nondegenerate, it also hints at the CPGE response stemming from the Berry monopole charge. Here, we explore the helicity-dependent optoelectronic response of the topological/Weyl semimetal RhSi via time-domain terahertz emission spectroscopy. The remarkable CPGE behavior in in-plane mode was experimentally demonstrated, whereas it did not exhibit notable signatures in out-of-plane mode. We further perform the photoemission measurement, together with optical simulation, to investigate the physical properties of chiral Weyl semimetal RhSi.