Arne Brataas, Emmanuel I. Rashba
Nuclear spin polarization can be pumped into spin-blocked quantum dots by multiple Landau- Zener passages through singlet-triplet anticrossings. By numerical simulations of realistic systems including approximately $10^7$ nuclear spins during $10^5$ sweeps, we uncover a mechanism of dynamical self-quenching which results in a fast saturation of the nuclear polarization under stationary pumping. This is caused by screening of the field of the nuclear spins. In systems with moderate spin-orbit coupling, self-quenching also screens the spin-orbit interaction. The mechanism is generic and remains robust under a moderate noise. Our finding explains low polarization levels achieved experimentally and calls for developing new protocols that break the self-quenching limitations.
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http://arxiv.org/abs/1206.0100
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