Optically patterned nuclear doughnuts in GaAs∕MnAs heterostructures

We demonstrate a scheme for optically patterning nuclear-spin polarization in semiconductor∕ferromagnet heterostructures. A scanning time-resolved Kerr rotation microscope is used to image the nuclear-spin polarization that results when GaAs∕MnAs epilayers are illuminated with a focused laser having a Gaussian profile. Rather than tracking the intensity profile of the laser spot, these images reveal that the nuclear polarization forms an annular lateral structure having circular symmetry with a dip rather than a peak at its center.