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

Abstract

We have used gated GaAs/Al${}_x$Ga${}_{1-x}$As 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 $V_t$ 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.