Bistable resistance switching in a ferromagnetic quantum Hall system induced by exchange enhancement of the Zeeman energy - art. no. 045306

We have studied the nonlinear current transport in Ga0.47In0.53As/Al0.48In0 .52As quantum-well structures near filling factor 1. A strictly bistable sw itching between the nearly nondissipative quantum Hall conduction and dissi pative 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 fil ling 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, wh ich depends on the degree of spin polarization. The hysteresis of the switc hing is accompanied by a partially ferromagnetic memory of the spin polariz ation when sweeping the external magnetic field. We have confirmed this ass umption by calculations applying a screened Hartree-Fock model. The calcula ted results are in good agreement with the data obtained experimentally for different orientations of the magnetic field. A possible conjunction of th e effect with nuclear spin magnetization was excluded by investigating the response of the bistable switching to exposure to radiation at the frequenc ies of the corresponding nuclear magnetic resonances.