Evidence for a phase transition in the fractional quantum Hall effect

We observe a novel transition between distinct fractional quantum Hall states sharing the same filling fraction =(8/5. The transition is driven by tilting the two-dimensional electron-gas sample relative to the external magnetic field and is manifested by a sharp change in the dependence of the measured activation energy on tilt angle. After an initial decline, the activation energy abruptly begins to increase as the tilt angle exceeds about 30°. A plausible model for these results implies a transition from a spin-unpolarized quantum fluid at small angles to a polarized one at higher angles.