Effects of in-plane magnetic fields on spin transitions in bilayer quantum Hall states

In a bilayer system, various phase transitions occur due to the competition among the cyclotron, Zeeman and tunneling energies. We investigate effects of an in-plane magnetic field B||, which couples subband and Landau levels with the same spin and modulate wave functions extended to both layers, on transitions of quantum Hall states in such a system. As B|| is applied, we observe that crossings between opposite spin levels as well as those between the same spin levels disappear in characteristic sequences. While anticrossings of single-particle levels are sufficient to explain the observed behavior for crossings at ν=4, the data at ν=6 are not understood in a single-particle picture, and suggest Coulomb-induced mixing of different spin levels.