Dynamic nuclear polarization at the edge of a two-dimensional electron gas

We have used gated GaAs/AlxGa1-xAs heterostructures to explore nonlinear transport between spin-resolved Landau level edge states over a submicrometer region of two-dimensional electron gas (2DEG). The current I flowing from one edge state to the other as a function of the voltage V between them shows diodelike behavior-a rapid increase in I above a well-defined threshold V, under forward bias, and a slower increase in I under reverse bias. In these measurements, a pronounced influence of a current-induced nuclear-spin polarization on the spin splitting is observed, and supported by a series of NMR experiments. We conclude that the hyperfine interaction plays an important role in determining the electronic properties at the edge of a 2DEG.