Circular Photogalvanic Effect in the Weyl Semimetal TaAs**Supported by the National Basic Research Program of China under Grant Nos 2015CB921300, the National Key Research and Development Program of China under Grant Nos 2016YFA0300300, 2017YFA0504703 and 2017YFA0302900, the National Natural Science Foundation of China under Grant Nos 11604372, 11474323 and 11774391, the Strategic Priority Research Program (B) of the Chinese Academy

Abstract

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. The generation of a sizable photocurrent is predicted in non-centrosymmetric WSM arising from the broken inversion symmetry and the linear energy dispersion that is unique to Weyl systems. In our recent measurements, the circular photogalvanic effect (CPGE) is discovered in the TaAs WSM. The CPGE voltage is proportional to the helicity of the incident light, reversing direction if the radiation helicity changes handedness, a periodical oscillation therefore appears following the alteration of light 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-related selection rule.