Optical pumping of dipolar order in a coupled nuclear spin system

Abstract

A possible mechanism for the direct generation of dipolar order in a coupled nuclear spin system by optical pumping is investigated theoretically. This work is motivated by recent optically pumped nuclear magnetic resonance experiments on single-crystal indium phosphide wafers, which have revealed that optical pumping can generate a state of nuclear spin dipolar order in a system of coupled spins without the application of radiofrequency fields or pulse sequences. The theory proceeds by evaluating the steady-state populations of the eigenstates of a coupled nuclear spin system when simultaneous nuclear and electron spin transitions are driven by fluctuating hyperfine couplings of the nuclei to an electron with a non-equilibrium spin polarization. In the case of two coupled spin-1/2 nuclei, substantial dipolar order results when the hyperfine couplings are of the dipolar, but not the Fermi contact, type.