Subband-Landau-level coupling in the fractional quantum Hall effect in tilted magnetic fields

We have studied the effect of subband-Landau-level coupling in the fractional quantum Hall effect in a tilted magnetic field. The quasiparticle-quasihole excitation gap for 1/3 and 2/3 fillings of the lowest Landau level show different angular dependence as the tilt angle is increased, consistent with the experimental observations. The breaking of the electron-hole symmetry at high magnetic fields is explained as a direct consequence of this coupling. For small values of tilt angle, spin-reversed quasiparticle excitations are found to influence the behavior of the energy gap.