Fractional quantum Hall effect in tilted magnetic fields

We have studied the dependence of the fractional quantum Hall effect on a tilted magnetic field. The activation energies for the Landau-level filling factors $\nu =\frac{2}{3}$ and $\nu =\frac{1}{3}$ have been measured. By tilting the field we could observe an increase of the activation energy for $\nu =\frac{2}{3}$, whereas the activation energy for $\nu =\frac{1}{3}$ decreased slightly. Changes could also be observed for the minima of the filling factors $\nu =\frac{4}{3}, \frac{5}{3}, \frac{2}{5}, \mathrm{and} \frac{3}{5}$. The data suggest a different behavior of "electronlike" fractional states and of "holelike" fractional states in a tilted field.