Dynamic Nuclear Polarization and Nuclear Fields

Abstract

The optical polarization of nuclear spins may develop in a semiconductor when it is illuminated by circularly polarized light (Lampel, Phys. Rev. Lett. 20, 491, 1968, [1], Optical orientation, 1984, [2]). The ultimate reason of this phenomenon is the hyperfine interaction of electron and nuclear spins, enabling the transfer of angular momentum (spin) from optically oriented electrons to the lattice nuclei. This process is called dynamic polarization. The dynamically polarized nuclei, in turn, produce a mean effective magnetic field (called Overhauser field) that can substantially change the spin polarization of electrons. In that way, a strongly coupled electron–nuclear spin system is formed, where the polarization of nuclei is not simply determined by the spin state of electrons, but exerts a back influence upon the electron polarization.