Nuclear spin polarization transfer with a single radio-frequency field in optically pumped indium phosphide

We describe a novel spin polarization transfer phenomenon observed in high-field, optically pumped NMR experiments on single-crystal indium phosphide. Polarization transfer from In-115 spins to P-31 spins occurs when a weak radio-frequency field is applied at the P-31 NMR frequency. Unlike other known high-field polarization transfer effects, no rf field near the In-115 frequency is required. We present evidence that the P-31 polarization arises from a state of optically pumped dipolar order in the In-115 spin system and propose two mechanisms that may contribute to the creation of this state. [S0031-9007(98)07539-5].