Bistable resistance switching in a ferromagnetic quantum Hall system induced by exchange enhancement of the Zeeman energy

Abstract

We have studied the nonlinear current transport in ${\mathrm{Ga}}_{0.47}{\mathrm{In}}_{0.53}{\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{0.48}{\mathrm{In}}_{0.52}\mathrm{As}$ quantum-well structures near filling factor 1. A strictly bistable switching between the nearly nondissipative quantum Hall conduction and dissipative conduction was observed at filling factors between 1 and 1.5 at the critical current. The steepness of the transitions was found to be sharper than 4 ppm (limited by the resolution of the setup) with respect to the filling factor. In contrast to thermal or density-distribution instabilities, which can lead to similar bistabilities at any integer filling factor, the effect observed in this study occurred exclusively around filling factor 1. Consequently, we attribute the switching to a feedback effect between the tunneling rate between different spin levels and the effective spin gap, which depends on the degree of spin polarization. The hysteresis of the switching is accompanied by a partially ferromagnetic memory of the spin polarization when sweeping the external magnetic field. We have confirmed this assumption by calculations applying a screened Hartree-Fock model. The calculated results are in good agreement with the data obtained experimentally for different orientations of the magnetic field. A possible conjunction of the effect with nuclear spin magnetization was excluded by investigating the response of the bistable switching to exposure to radiation at the frequencies of the corresponding nuclear magnetic resonances.