Selective dynamic nuclear spin polarization in a spin-blocked double dot

We study the mechanism of dynamical nuclear spin polarization by hyperfine interaction in a spin-blocked double quantum dot system. We incorporate the effects of the nuclear quadrupole coupling due to the doping-induced local lattice distortion and strain, and propose a new spin depolarization channel due to quadrupolar state mixing and hyperfine coupling. We calculate the hyperfine transition rates and solve the master equations for the nuclear spins. Our results show that nuclear quadrupole coupling induced by the 5% indium doping can lead to significant nuclear spin relaxation, and thus can be used to explain the recent experimental observation of missing arsenic NMR signal in the spin-blocked double dots.