Two-dimensional nuclear magnetic resonance spectroscopy in optically pumped semiconductors

Optical pumping enhanced double quantum nuclear spin coherences were detected in bulk GaAs and InP by two-dimensional NMR. The stimulation of the coherences was achieved using a single non-selective resonant RF pulse. This is unusual because stimulation of such coherences from a spin system at thermal equilibrium in high field would normally require a minimum of two pulses. A density matrix analysis, combined with a time-resolved study of the build-up of the double quantum coherence in GaAs, suggests that the enhancement of the double quantum coherence amplitude stems from optical pumping of dipolar nuclear spin order.