No abstract

No abstract

Observations are reported of nuclear magnetic resonance (NMR) for nuclei in single GaAsIAIGaAs quantum wells, using an optical pumping and detection scheme. The technique gives signals only from nuclei in contact with the quantum-confined electron wavefunction and therefore discriminates against substrate and barrier nuclei.Some general factors which affect the strength of signals are discussed and preliminary results are presented which show the potential of NMR for measuring strain in pseudomorphic systems and for detecting and identifying impurities.

Optical pumping can increase the polarization of nuclear spins in semiconductors such as GaAs by many orders of magnitude, improving the sensitivity in conventionally detected nuclear magnetic resonance ͑NMR͒ experiments. Optical detection of these NMR transitions provides an additional increase in sensitivity, and furthermore, can distinguish signal contributions from different quantum wells in multiple quantum well samples. In this article we study the coupling mechanisms for all-optical NMR experiments, where modulation of the cw optical excitation at the nuclear Larmor frequency induces transitions between the nuclear spin states. We find clear evidence for two different types of interaction between the photogenerated carriers and the nuclear spins: the hyperfine interaction and the coupling between the electric field of the electron and the nuclear quadrupole moment. While the former induces only ⌬m I ϭϮ1 transitions, the latter also causes ͑single photon-͒ ⌬m I ϭϮ2 transitions.

No abstract

No abstract

No abstract

No abstract