Interplay of spin-orbit and hyperfine interactions in dynamical nuclear polarization in semiconductor quantum dots

We theoretically study the interplay of spin-orbit and hyperfine interactions in dynamical nuclear polarization in two-electron semiconductor double quantum dots near the singlet $(S)$ - triplet $(T_+)$ anticrossing. The goal of the scheme under study is to extend the singlet $(S)$ - triplet $(T_0)$ qubit decoherence time $T_2^{*}$ by dynamically transferring the polarization from the electron spins to the nuclear spins. This polarization transfer is achieved by cycling the electron spins over the $S-T_+$ anticrossing. Here, we investigate, both quantitatively and qualitatively, how this hyperfine mediated dynamical polarization transfer is influenced by the Rashba and Dresselhaus spin-orbit interaction. In addition to $T_2^*$, we determine the singlet return probability $P_s$, a quantity that can be measured in experiments. Our results suggest that the spin-orbit interaction establishes a mechanism that can polarize the nuclear spins in the opposite direction compared to hyperfine mediated nuclear spin polarization. In materials with relatively strong spin-orbit coupling, this interplay of spin-orbit and hyperfine mediated nuclear spin polarizations prevents any notable increase of the $S-T_0$ qubit decoherence time $T_2^{*}$.

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