Strong, ultranarrow peaks of longitudinal and Hall resistances in the regime of breakdown of the quantum Hall effect

With unusually slow and high-resolution sweeps of magnetic field, strong ul tranarrow (width down to 100 mu T) resistance peaks an observed when high c urrents are applied through quantum Hall samples. The peaks are dependent o n the directions and even the history of magnetic field sweeps, indicating the involvement of a very slow physical process. Such a process and the sha rp peaks are, however, not predicted by existing theories. We also find tha t the sharp resistance peaks are influenced by the nuclear spin flips.