On the upper limit for optical spin pumping in III-V semiconductor quantum dots

We studied the optical steady-state generation of spin in the III-V semiconductor quantum dots, where an external laser field couples to the quantum dot only via the electric dipole interband transition and generation of spin in the conduction band is due to the optical transition from the spin-split valence band. In the weak field regime, the optical spin generation is second order in the Rabi frequency. At the intense laser fields, the spin-orbit interaction is of no importance and the optical spin generation is absent. Therefore, there should be a region featured by intermediate Rabi frequencies where the optical spin generation reaches its maximum. We demonstrated this upper limit using a simple model of the III-V quantum dot. The maximum corresponds to the optical interaction energy equal to the spin-orbit interaction energy in the valence band. The work addressed here sets the upper limit for steady-state optical spin generation in the III-V semiconductor quantum dots and completes the physical picture of this process for all optical field strengths. (C) 2011 American Institute of Physics. [doi:10.1063/1.3567303]