Nuclear polarization in quantum point contacts in an in-plane magnetic field

Nuclear spin polarization is typically generated in GaAs quantum point contacts (QPCs) when an out-of-plane magnetic field gives rise to spin-polarized quantum-Hall edge states and a voltage bias drives transitions between the edge states via electron-nuclear flip-flop scattering. Here, we report a similar effect for QPCs in an in-plane magnetic field, where currents are spin polarized but edge states are not formed. The nuclear polarization gives rise to hysteresis in the dc transport characteristics with relaxation time scales around 100 s. The dependence of anomalous QPC conductance features on nuclear polarization provides a useful test of their spin sensitivity.