Optical spanner based on the transfer of spin angular momentum of light in semiconductors

An optical spanner is a light beam that can exert a torque on a microscopic object. When a circularly polarized beam irradiates semiconductors, the output light becomes partially circularly polarized. Thus the total angular momentum of the light beam is changed, which leads to a torque, creating an optical spanner on the semiconductor. In this letter, we investigate this kind of optical spanner in detail, and its electric and magnetic control are discussed.