Hysteresis and Spin Transitions in the Fractional Quantum Hall Effect

We have observed hysteretic behavior associated with spin transitions in the fractional quantum Hall effect (FQHE). Dramatic hysteresis in up and down sweeps of the magnetic field occurs in the vicinity of the spin-polarized to spin-unpolarized transitions in even-numerator FQHE states. The hysteresis is most pronounced at the lowest temperatures and disappears as the temperature is raised. These results suggest that the FQHE states exhibit metastability in close proximity of the spin transitions. We discuss our findings in terms of a recent proposal of ferromagnetlike ordering associated with nearly degenerate Landau levels.