Atomic and Molecular Physics(DAMP)
Physique atomique et moléculaire (DPAM)
John E. SIPE
University of Toronto
Optically injected spin currents in semiconductors
It has been widely known since the 1980’s that carriers with a net spin polarization can be optically injected in semiconductors, such as GaAs, simply by irradiation with circularly polarized light at energies above the band gap. Indeed, such injection followed by acceleration of the injected carriers by an applied DC field is nowadays a standard approach to generating a spin-polarized current. But only recently has it been appreciated that spin currents themselves can be optically injected in semiconductors directly, in the absence of a bias field.
Our work has focused on optical injection across the band gap, using quantum interference effects associated with different pathways connecting the same initial and final states. Simultaneous irradiation by beams at ? and 2?, where 2? crosses the band gap, allows for the interference of one- and two-photon absorption processes. With a proper choice of a relative phase parameter net currents can be injected in the crystal; this injected current can be spin-polarized. In a difference scenario, carriers injected at k are injected preferentially with one spin polarization, and those at -k with the opposite. No net electrical current or spin is injected into the crystal, but a pure spin current is.
Theoretical and experimental work will be reviewed, and new scenarios involving laser light of only one frequency will be discussed.
*Work done in collaboration with R.D.R. Bhat, Ali Najmaie, F. Nastos, Y. Kerachian, and H.M. van Driel at the University of Toronto, and A.L. Smirl, M.J. Stevens, and X.Y. Pan at the University of Iowa.