Event

In light-matter interaction, the conservation of angular momentum requires the angular momentum transfer between light and matter, which consequently couples light polarization to various state variables of materials, such as mechanical motion, magnetization or charge current, and gives rise to a plethora of intriguing phenomena. In this talk, I will discuss the angular momentum transfer in two different scenarios with a focus on the roles of photon and electron spin.

First, I will present the measurement of spin angular momentum of light propagating in a silicon waveguide. The continuous evolution of light polarization along propagation results in the exchange of angular momentum between light and medium and thus an optical torque to twist the waveguide. I will demonstrate the use of optical torque to excite the torsional motion of an on-chip optomechanical device, which enables the coupling between optical and mechanical degrees of freedom. Second, I will show the optical manipulation of surface electrons in 3D topological insulator Bi2Se3 using circularly polarized light. The transfer of angular momentum manifests itself in the spin-dependent optical selection rules and the generation of helicity-dependent photocurrent at zero bias voltage.