  Novel fermions with relativistic linear dispersion can emerge as low-energy
excitations in topological semimetal materials. Here, we show that the orbital
moment contribution in the circular photomagnetic effect for these topological
semimetals exhibit an unconventional $\omega^{-1}$ frequency scaling, leading
to significantly enhanced response in the low frequency window, which can be
orders of magnitude larger than previous observations on conventional
materials. Furthermore, the response tensor is directly connected to the Chern
numbers of the emergent fermions, manifesting their topological character. Our
work reveals a new signature of topological semimetals and suggests them as
promising platforms for optoelectronics and spintronics applications.
