Simultaneous excitation of spins and pseudospins in the bilayer ν = 1 quantum Hall state

The tilting angular dependence of the energy gap was measured in the bilayer quantum Hall state at the Landau level filling ν=1 by changing the density imbalance between the two layers. The observed gap behavior shows a continuous transformation from the bilayer balanced density state to the monolayer state. Even a sample with 33 K tunneling gap shows the same activation energy anomaly reported by Murphy et al. (Phys. Rev. Lett. 72 (1994) 728). We discuss a possible relation between our experimental results and the quantum Hall ferromagnet of spins and pseudospins.