Continuous transformation from spin- to pseudospin-type excitation

We measured the activation energy of bilayer ν = 1 quantum Hall states. By changing the density difference between layers, the tilting behavior of the pseudospin(P)-type activation energy at the equal density point gradually transforms into the spin(S)-type one at the monolayer density point. At the intermediate density difference, by increasing the tilting angle the activation energy starts to decrease as the P-type excitation gap and then increases as the S-type excitation gap. It is impossible to explain this behavior by the level crossing of the P- and S-type excitations. The result of the overall behavior indicates the excitation in a bilayer system is the simultaneous flip of spin and pseudospin.