Dynamic nuclear polarization induced by hot electrons

A new method for local dynamic nuclear polarization is demonstrated in a GaAs/AlGaAs heterostructure at the Landau level filling factor $\nu=3$. Using a narrow channel sample, where the width varies stepwise along the electron flow, we find that electron cooling (heating) causes the polarization of nuclear spins against (toward) the external magnetic field at liquid helium temperatures. The longitudinal nuclear spin relaxation rate varies exponentially with inverse temperature.