Evidence for an electric-field-induced phase transition in a spin-polarized two-dimensional electron gas

A junction between two coplanar two-dimensional electron gases in a ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/GaAs heterostructure at which the Fermi level crosses between adjacent spin-split Landau levels has remarkable current-voltage characteristics: current is time dependent, a consequence of dynamic nuclear polarization at the junction. Also, when biased so as to increase the junction electric field, the junction exhibits a series of abrupt transitions between distinct states, an effect that we attribute to an electric-field-induced phase transition of the spin-polarized electrons at the junction.