Landau Level Spectroscopy by Optical Vortex Beam

The optical vortex beam carries the orbital angular momentum ℓ in addition to the spin angular momentum σ. We propose that the existence of finite ℓ is demonstrated through modified selection rules for absorption processes of the optical vortex by the Landau-quantized two-dimensional electron gas. We show that the lowest Laudau level electrons absorb the optical vortex beams with σ = 1 (positive helicity) and ℓ=0 or σ = −1 (negative helicity) and ℓ=2. This means that the intrinsic spin (helicity) and the orbital angular momentum of the optical vortex are tied to each other in the absorption processes. It is also shown that the electric currents induced by the optical vortex are distributed along the edge of the sample. Reflecting the spatial profile of the optical vortex beam, the induced current disappears when the dark rings of the beam coincide with the circular edge.