We have measured activation energies for fractional-quantum-Hall-effect (FQHE) states with a magnetic field added in the plane of the two-dimensional electron gas. Our data are incompatible with calculations of the expected finite-size corrections due to the added parallel field. Instead, the activation energies for some FQHE states depend linearly on the total magnetic field; others depend only on the perpendicular magnetic field. These dependencies indicate that spin-flip excitations are important for certain FQHE gaps.
- Received 22 August 1988
- Published in the issue dated 4 September 1989
© 1989 The American Physical Society