Bilayer ν=2 quantum Hall state in parallel high magnetic field

Abstract By tilting the sample as well as by varying density difference between the two layers, we have measured the activation energy of a bilayer quantum Hall state as a function of the total magnetic field. Let Θ be the tilt angle. When the densities are balanced, the activation energy begins to increase linearly beyond a certain critical angle Θ ∗ as the total magnetic field increases. The slope of the curve is 5.6|g ∗ |μ B , from which we conclude that a skyrmion pair with spin 5.6 is excited. On the other hand, as the density difference increases, the activation energy decreases rapidly and eventually disappears. These results imply that the bilayer QH state is not a coherent state but rather a compound state beyond the critical angle ( Θ>Θ ∗ ).