Collapse of the even-denominator fractional quantum Hall effect in tilted fields.

Abstract

The newly discovered even-denominator fractional quantum Hall effect at filling factor $\ensuremath{\nu}=\frac{5}{2}$ is found to collapse rapidly as the magnetic field is tilted away from the normal to the two-dimensional-electron-gas plane. No similar effect has been reported in tilted-field studies of the spin-polarized, odd-denominator effect at $\ensuremath{\nu}=\frac{2}{3} \mathrm{and} \frac{1}{3}$. Since a primary result of such tilting is increased spin splittings, the collapse of the $\ensuremath{\nu}=\frac{5}{2}$ effect strongly suggests that the underlying state is not spin polarized. Condensation into such a quantum liquid must involve substantial spin reversal.