Nuclear Spin Induced Oscillatory Current in Spin Blockaded Quantum Dots

Hyperfine interactions between electron and nuclear spins in quantum dots are subject to intensive studies from the viewpoints of quantum computing. In this talk I will review our recent experimental studies for a GaAs-based double quantum dots in the spin blockade regime where the electron conduction is mostly blocked by Pauli effect unless the electron spin state is changed [1]. Thus a small leakage current observed in the spin-blockaded double dot can be a sensitive measure not only for electron spin-flip events but also for a nuclear spin states in the dot if the spin-flip is mediated by hyperfine interactions. We have observed the leakage current shows time-dependent oscillations and is significantly diminished by application of an AC magnetic field whose frequency can induce nuclear magnetic resonance for 71Ga and 69Ga nuclei [2]. A possible nuclear spin polarization mechanism due to hyperfine flip-flop scattering is proposed. [1] K. Ono et al., Science, 297, 1313 (2002). [2] K. Ono et al., Phys. Rev. Lett 92, 256803 (2004). cond-mat/0309062.