  Weyl semimetal (WSM) is expected to be an ideal spintronic material owing to
its spin currents carried by the bulk and surface states with spin-momentum
locking. A photocurrent generation in noncentrosymmetric WSM was also predicted
owing to its broken inversion symmetry and linear energy dispersion which are
unique to Weyl systems. In our recent measurements, the circular photogalvanic
effect (CPGE) has been demonstrated in WSM of TaAs. The CPGE voltage is
proportional to the helicity of the incident light and reverses its direction
on changing the radiation helicity from left handed to right handed, a
periodical oscillation therefore appears following with the alteration of
optical polarization. We herein attribute the CPGE to the asymmetric optical
excitation of the Weyl cone, which could result in an asymmetric distribution
of photoexcited carriers in momentum space according to an optical spin
selection rule.
