Mapping the Spin-Injection Probability on the Atomic Scale

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A spin-polarized electron current is injected into the GaAs(110) surface at 100 K by using a polycrystalline ferromagnetic Ni scanning tunneling microscopy (STM) tip. The injected electrons recombine to the valence band and emit circularly polarized radiation whose degree of light polarization is related to the polarization of the conduction-band electrons at the instant of recombination. When the polarized electrons are injected into clean, flat terraces an average polarization for the emitted radiation is found to be 6.79%, while over the 10-nm step region the polarization is reduced to 0.46%. This step scattering effect is studied further by varying the tunneling gap through adjusting the tunneling current. As the distance between the STM tip and sample decrease the spin-scattering effect of the step edge is enhanced.

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