Oscillatory spin asymmetric scattering of low-energy He+ ions on Sn surfaces

Spin-polarized He+ ion scattering spectroscopy (SP-ISS) study on a polycrystalline Sn target surface is reported. We observed substantial spin dependent He+ ion scattering on the non-magnetic Sn target. It is not due to He+ ion neutralization, but it is attributed to spin-orbit coupling (SOC) that acts transiently on the He+1s electron spin in the He+-Sn atom binary collision. We found that the spin dependent scattering quantified as the spin asymmetry exhibits periodic oscillation with the reciprocal of the He+ ion velocity. The oscillation originates from the SOC induced-slight energy difference of the [He+-Sn] and [He0-Sn+] systems which are involved in the quasi-resonant charge transfer. The oscillatory spin asymmetry shows that SOC arises from collision induced intermediate state.