Spin current in the quantum Hall regime detected by dynamic nuclear polarization

Spin current and heat flow in the spin-resolved quantum Hall regime around Landau level filling factor ν=3 are studied in GaAs/AlGaAs two-dimensional electron systems. We demonstrate that dynamic nuclear polarization (DNP) can be caused by an electron temperature change in the breakdown regime at ν=3 using a narrow channel sample where the width varies stepwise along the electron flow. We also investigate the spin current perpendicular to the electron flow using a specially designed Hall bar for the detection of DNP in the vicinity of one of the edges. The observed polarity of DNP indicates that the directions of the spin current and the Hall electric field are the same for ν>3, but are opposite for ν<3.