Ettingshausen Effect around Landau Level Filling Factor nu=3 Studied by Dynamic Nuclear Polarization

Spin current perpendicular to the electric current is investigated around Landau level filling factor $\nu=3$ in a GaAs/AlGaAs two-dimensional electron system. Measurements of dynamic nuclear polarization in the vicinity of the edge of a specially designed Hall bar sample indicate that the direction of the spin current with respect to the Hall electric field reverses its polarity at $\nu=3$, where the dissipative current carried by holes in the spin up Landau level is replaced with that by electrons in the spin down Landau level.