Dynamic nuclear spin polarization induced by Edelstein effect at Bi(111) surfaces*

Nuclear spin polarization and its Overhauser field, induced by hyperfine interaction and the Edelstein effect, were investigated by quantum transport in individual micrometer-sized Bi(111) thin film samples. A high current density was applied at low temperatures to generate a non-equilibrium carrier spin polarization in the Bi(111) surface states by the Edelstein effect and strong spin-orbit interaction, which then induced dynamic nuclear polarization by hyperfine interaction. The antilocalization magnetotransport measurements showed that as the polarization duration or the polarization current increased, the carrier quantum phase decoherence times decreased while the spin-orbit decoherence times increased, which allowed a quantification of the Overhauser field from the nuclear polarization. By using delay times between polarization and measurement, an exponential decay of the Overhauser field was observed, driven by a nuclear spin relaxation time. Application of an external magnetic field during polarization showed that the carrier spin polarization itself was sufficient to overcome dipolar interactions between nuclear spins. Comparative studies of the transport properties of Bi(111)-on-mica and Bi(111)-on-Si(111) will also be discussed.